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Computer Programming with GNU Smalltalk

1. Maybe one more example may help you understand it better aSet add Toothpaste Toothpaste aset set Soap Toothpaste Toothbrush Now the last object we added went in between the other two old objects But again this is just a representation actually they don t have any order There is an interesting result of not having an order inside Set object When you try to add the same object twice into a Set object you end up having it only once aSet add Toothbrush Toothbrush aSet Set Soap Slookhpasie Toothbrush What does matter to the GST is if an object is in the Set or not As you can see this is much like the sets in mathematics remove To remove an element from a Set you can use the remove message aSet remove Toothpaste Toothpaste Note that remove message didn t return the Set object instead returned the removed object aSet set Soap Toothbrush e 40 Computer Programming with GNU Smalltalk As you see we didn t use an index to reach and remove the element instead we used the element itself because elements inside a set does not have an index Note that removing an element from a set does not necessarily delete that object from the system The object just does not belong to that set anymore Let s demonstrate that anElement anElement Perfume Perfume We created a separate variable pointing to a St ring object Now add it to our set aSet a
2. SubclassName class gt gt aClassMethod aParameter Comment to describe this class method category Category of this class method localVariablel localVariable2 objectToReturn We again have a header part and a body part here The header of the class definition is SubclassName class aClassMethod aParameter SubclassName class part of this header tells us that we are going to create a method for the class not for the instances of the class If we d omitted this part then the method would be a part for the instances of this class After this part we specify our method s message The selector of this message is aClassMethod It takes a parameter named aParameter Parameters are the names given to the argument names when they are used in the header of methods so these words are actually not that different from arguments and sometimes used in exchange We may use the parameter names inside our method to refer to the argument passed to the method After specifying the selector we opened the bracket to define the method content which is called the body of the method Comment to describe this class method category Category of this class method localVariablel localVariable2 objectToReturn The content of a method can be made of a comment a category some local variables and the expressions to execute which are shown as three dots After writing a comment with 62 Computer Programmin
3. instanceVariablel instanceVariable2 classVariablel anObject classVariable2 anotherObject comment Comment to describe our class gt SubclassName class gt gt aClassMethod aParameter Comment to describe this class method category Category of this class method localVariablel localVariable2 objectToReturn anInstanceMethod Comment to describe this instance method category Category of this instance method localVariablel localVariable2 objectToReturn Above pseudo code shows how to create a class add class and instance variables add class and instance methods to it We will explain it line by line but before that we want to mention about some general concepts Most of the things above are optional for example you don t need to have class variables or methods Or you don t need to write comments for anything or define the category of a method But these are good software engineering habits and we recommend you to always write comments and define categories for methods Also another interesting thing in above code is the usage of white spaces Some lines are indented by tabs or spaces but why is that It is just because for polishing the code for human eye and there is no tule for how to use them Mostly we will indent a body of some new structure For example when we are writing the body of a class then we will indent it one level compared to the context Interpretation of on
4. Now let s add another St ring object aDictionary at Paolo put Bonzini DE onze aDictionary Dictionary Canol Gokel UE oU Eon keys We can get all the keys inside a Dictionary by using keys message GST will return a Set object which includes all the keys aDictionary keys Sue GuCano la GE ao osm removeKey To remove an element from a Dictionary you can use the removeKey message 42 Computer Programming with GNU Smalltalk aDictionary removeKey Canol Gone aDictionary IbitenestHerseues i Iljeieroylel es Viexeyatezabglat V removeKey message like remove message from Set returned the removed object Review Questions 1 What is an object a message and a class 2 What is a variable Why do we need them 3 What are the types of messages Can you classify two messages for each of the type among the messages we saw on section Common Classes and Their Usage 4 What type of numbers can we deal with in GNU Smalltalk Give some example numbers for each type 5 Write a program which gets a number from user and displays its cube 6 Write a program which gets two numbers from the user separated by a space and displays their arithmetic average Hint You will get an input like 3 4 from the user which is a String holding two numbers Use tokenize aString message on this string to separate the numbers from each other tokenize message separates a string into pieces whic
5. This is because although a name refers to only one object the object it refers to can be changed any time in the program Before learning how to assign a name to an object first discuss why would we want to do such a thing Most probably in an example like above which we created a human you wouldn t want to change the referred object But let us take another example suppose that we have a program which tracks the number of customers who visits a restaurant in a day This program should increment the number by one every time a customer comes in How can we achieve such a mission Well first we create a variable which refers to object 0 Than every time a customer comes in we call that variable get the object it refers sum it with 1 and assign it back to that variable So every time a customer comes in the object variable refers to is changing Now it is time to learn the syntax for doing assignment Before doing any assignments we should create variables The general structure for creating variables is aVariable anotherVariable andAnotherVariable Here we created three variables named aVariable anotherVariable and andAnotherVariable We put the variable names we want to create between pipe characters We separate variables with spaces and can create as many variable as we want The general syntax for assignment is like this aVariableName anObject We use an operator called assignment operator which is composed of a colon and an
6. cat Cat new Animal setAnimalNumber 2 cat setName Minnosh cat getName printNl cat makeNoise We first created a Dog object then set the animal number to 1 and the name of the dog to Karabash Then we printed the name of our dog and made her bark Secondly we created a Cat object and applied the same process we applied onto our dog This time we chose the name Minnosh and set the animal number to 2 because we now have two animals For experienced programmers Actually the inheritance tree and other things like manually updating the animal number is of course a bad programming practice in real applications but we wanted to keep the sample simple The last statement merely prints the animal number which is kept inside our Animal class Animal getAnimalNumber printNl With this example we have seen inheritance via the accessor methods Accessor methods provided us communication with the inner status of the object which is composed of the class and instance variables We ve also seen polymorphism via the makeNoise method which behaves differently according to the class of the object we are sending the message to And we ve lastly seen the inheritance concept by observing the presence of the setName and getName methods on every class which is derived from Animal class Extending and Modifying Classes Suppose you are going to use a number s cube in your program a lot Wouldn t it be great to have a meth
7. that they created simple text files Text files include just alphanumerical characters and some special control characters which are all presented according to a special encoding system which are called character encoding The characters they can include are limited with the capabilities of the character encoding they use A list of characters which can be presented are listed in tables called character sets Every character is presented with a number in a character set There are special programs called text editors which are capable of reading and writing text files The most commonly used character encoding is ASCII American Standard Code for Information Interchange which uses a simple encoding that can be expressed in a single sentence Every character is presented in seven bits A text editor which supports ASCII character encoding can read any ASCII encoded text file This along with the simplicity of the character encoding specifications provide an enormous portability between digital equipment You can find the ASCII table at Appendix B of this text Because ASCII has a 7 bit limit and you can only write 128 different number with 7 bits ASCII can represent only up to 128 different characters The world is big and there are hundreds of different alphabets with thousands of different characters There are some languages which use alphabets that have more than 128 characters so it might be even impossible to represent a single alphabet in a 7
8. I m 24 years old I am an Engineer Hello my name is Ismail Arslan and I m 23 years old I am an Engineer false The difference is that we used the self keyword to reach the attributes of our object instead of using them directly For example self getName means Send the message getName to the receiver object The trick here is that the search for the method will begin directly at the class of the receiver object and continue to its ancestors until a definition is found Remember this because it is the difference between self and super keywords 74 Computer Programming with GNU Smalltalk We suggest you to use the accessors to handle the attributes like the above example even if you are in the class definition and be able to reach the attributes directly This is the encapsulation property of object oriented design and a good programming practice because in real life you cannot know what is going to happen inside an object if you change something in it For example think that you have a Molecule object When you add atoms in it a lot of properties of the molecule might also change like the bond type the geometrical shape etc So you shouldn t just do oxygen oxygen 1 you should use something like addOxygenAtom which takes care of all the details that you cannot predict or remember Of course at some point you have to use direct manipulation like in setters or getters itself but abstract as much as you can super When w
9. Let s look at the result of this code 3 between 4 and 6 false As you can see it is represented by an object named false We will see how to use this Boolean objects more detailed on Chapter 4 Controlling the Flow of Execution abs We use abs message to get the absolute value of a negative number 3 abs 3 28 Computer Programming with GNU Smalltalk degreesToRadians We can convert a magnitude in degrees to a magnitude in radians by using degreesToRadians message This will be useful for doing some trigonometric calculations 180 degreesToRadians Sio LAE OI oss Seo 70s GST calculated pi number quite accurately and quite fast didn t it cos We can calculate cosine of an angle with cos message 180 cos 0 5984600690578581 Wait a minute isn t the cosine of 180 1 Be careful of units cos message wants to be sent to a magnitude of radians not degrees So you have to first convert it into radians with degreesToRadians You will see how to use the result of degreesToRadians message to be sent cos message later negated We use negated message to find out the negative of a number 3 negated Watch out If you send this message to an already negative number then you will get the positive of that number 3 negated S raisedTo To find out the nth power of a number we use raisedTo message 3 rasiedTo 4 81 As you know Oth power of a number is always 1 3 raisedTo 0 ai Objects
10. Smalltalk true anArray includes Toothpaste false reverse Remember we said that Array objects are ordered collections There are ways to manipulate this order One of them is to reverse it via reverse message anArray reverse nose mister mim id eme SS SodpiE hoot hiybusrn ms Set Sets are a lot like Arrays except that they do not hold their content in any order and they don t have any predefined limits like Arrays A Set is the GNU Smalltalk counterpart of the sets in mathematics so it behaves much like the sets in mathematics new We create a Set instance again with new message but without an argument this time aSet aSet Set new Set The output shows us that initially our set does not contain any object in it add We can add an object into a Set by using add message aSet add Toothbrush Toothbrush aSet Set toothbrush Now our set holds a String object which has the value of Toothbrush Now let s add another String object aSet add Soap uo OSp Objects Messages and Classes Part 39 aSet Set Soap toothbrush As you can see GST put it before the Toothbrush object Actually it didn t put it before it just put it into the set randomly The place of Soap or Toothbrush object is unpredictable in other words they don t have any certain placement inside the Set Question Can you tell why Set class does not have a reverse method
11. a program written in an interpreted language if there is an interpreter for it on the computer you are working on The hardware you have or the operating system you use does not matter If you had programmed the software with a compiled language you should have done compilation first for the processor and operating system you have before launching the program This has its own advantages like being executed much faster after compilation and disadvantages like compiling the program every time you make a change in source code and every time you move your program from one platform to another Compiling a program into byte code speeds up this interpretation process and still has the advantages of an interpreted language Although GNU Smalltalk functions more like an interpreter Smalltalk is designed as a language which uses a virtual machine We can give Java programming language as an example of this type of languages and a very successful one indeed Procedural Functional and Object Oriented Programming Another categorization of programming languages are according to their paradigms A programming paradigm is how a programming language looks at the problems to be solved There are mainly 3 types of programming paradigms Procedural functional and object oriented To keep it simple and not confuse you with words you don t know yet we will only mention about object oriented programming which is the heart of Smalltalk language Object oriented pr
12. bit encoding That s why there are a lot of different character sets and encodings For example UTF 8 character encoding which may be used along with Unicode character set can represent characters via to 4 bytes Unicode character set has a character collection of about 100 000 characters Our GNU Smalltalk interpreter can read text files encoded with ASCII or UTF 8 so it would not be a problem whether your editor supports ASCII or UTF 8 Word Processors Text Editors and IDEs We will type our source codes into text files and we are going to use a program to write our source codes just like we use a program to create documents When typing is in discussion most probably a word processor like Microsoft Word iWork Pages or OpenOffice org Writer comes to an average computer user s mind But word processors are not created for simple text files They use binary files to keep the fancy document formatting like bold big colored text images and the layout of this kind of things They most probably have an option for creating plain text files but then we can t take advantage of the usefulness and speed of text editors This is like using a limousine to harvest Text editors provide an easy to use and fast solution for a programmer There are also some text editors 10 Computer Programming with GNU Smalltalk which are especially designed for programmers They have some useful features to make a programmer s life easier So we will use t
13. deeply There are actually two parts of this message One is a selector which is character and the other is an argument which is the object 4 You can get the selector by removing argument parts of the message We will give an example for that later Selectors form a system to help objects decide how to respond to messages For example here 20 Computer Programming with GNU Smalltalk selector is actually defined in object 3 so that 3 knows what to do when it receives this message Arguments are the additional data the object should use while evaluating the response Objects know how to use these additional data while evaluating the response We will see how objects know all about these when we see how we can define our custom objects Note that a message don t have to have any arguments Actually we will try a message without an argument next Here it is Hello World size 12 Here we have a string object Hello World and a message size This message tells string objects to return their length in other words how many characters they have As you can see size message does not have any arguments because it does not need to in other words it has all the information needed in other words the answer is in the question alright it s enough Let s look at one last example and then we will mention about message types We said that computers understand only ones and zeros So the number 3 is actually written to the memory of
14. equal sign without any whitespace in between This operator assigns the object on its right to the variable on its left Every object created occupies space in computer memory and the task of variables is actually to hold the memory address of an object Getting User Input In this section we will introduce a code to obtain information from user via standard input device most probably keyboard If you ever used a console program before then you probably faced Are you sure you want to do this y n kind of questions which expect you to enter y or n This is the technique used for getting that kind of user inputs from terminal user input st A program to demonstrate how to get input from user userName 36 Computer Programming with GNU Smalltalk Transcript show What is your name userName stdin nextLine Transcript show Hello userName cr What is your name Canol Hello Canol This program asks user for his her name and displays a hello message including the name entered The part which gets the user input is userName stdin nextLine stdin nextLine expects a keyboard input which is terminated by a newline character The user in this case enters whatever he she wants and presses Enter key to terminate the input process stdin nextLine returns the input string so we assigned it to the variable userName Assignment operator has a lower precedence compared to sending any kind of message to an
15. example Car is a Vehicle Second an object can consist of other objects This is called has a relation For example Vehicle has a Body The inheritance concept is related with is a relation and not has a relation 58 Computer Programming with GNU Smalltalk Multiple Inheritance and Single Inheritance Some programming languages allow programmers to create classes which inherits properties and behavior from more than one class So some classes have more than one superclass This is called multiple inheritance Other inheritance type which allows only one superclass per class is called single inheritance The examples we have given so far are of single inheritance and the examples we will give from now on will also be of single inheritance because Smalltalk uses single inheritance to manage classes It is still very arguable whether multiple inheritance is needed in object oriented design or only makes the inheritance more complex Polymorphism In a world full of different kinds of objects some objects may response the same message although they are different kind of objects meaning they are instances of different classes That s why some programming languages allow us to define methods with same selector in different classes Or they allow a subclass to change a selector s behavior which it inherited from its superclass This is called polymorphism Note The special case where a subclass changes the behavior of a method it
16. human languages as higher level it is Below you see what a machine code looks like 011010111010001011000101 You cannot even guess what this means right Now below we will give an example how the language called Assembly looks like 2 Computer Programming with GNU Smalltalk MOVE d 3 W ADD d 4 I don t know if you can guess what this code does but it is obvious that it is more readable than a machine code So we can say that Assembly language is a higher lever language than machine code By the way if you are curious about what the code above does it just sums up two numbers Now look at the same code above written in a language named GNU Smalltalk Hmm I never heard of it before 3 4 I won t ask if you have guessed what the code above does because I don t know of any way to describe it better than the code line above if you say no So the highest level language when we compare machine code Assembly and GNU Smalltalk is GNU Smalltalk Although the examples we have given to describe the language levels are pretty simple and obvious don t expect GNU Smalltalk as almost the same with English It can get sometimes as confusing as Assembly although it has a reputation as being a very high level language compared to other programming languages commonly used today We will finish this topic with an important statement being a higher level language does not mean being a better language Assembly is also a very commonl
17. inherited from its superclass is named as overriding We will now give a classical but very explanatory example for this concept Think of a class called Animal and its two subclasses Dog and Cat A method we would implement in Animal class would be speak because every animal communicates somehow with other livings by making some kind of noise although dogs prefer to bite sometimes But when this message is sent dogs would bark while cats would miaow So they response to the same message but in a different way Creating Your Own Classes GNU Smalltalk has hundreds of classes built in but the universe has uncountable of them so GNU Smalltalk gives us the opportunity to create the classes we want for our needs We will sometimes call the classes we made as custom classes First we should talk about what classes are made of Classes are the blue prints of objects so they definitely should describe all the things that objects have For example they have instance variables to define the properties of an object They should have method definitions to make objects responsive to some certain messages But they have more There are class variables Class variables hold the information about the state of the class There are also class methods which only classes can execute and not the instances of them Objects Messages and Classes Part ll 59 The general syntax for creating classes is below SuperclassName subclass SubclassName
18. interpretation process is called source code definitions at virtual machine put The converting process from byte code to machine code is done by programs called virtual machines definitions at cross platform put Cross platform is the name for being able to run a software on different computer architectures like different operating systems or different processors Transcript show Please enter a word to get its definition theWord stdin nextLine Transcript show theWord definitions at theWord asLowercase cr Please enter a word to get its definition programming language programming language We call the command groups which provide a communication between us and computer hardware as programming languages We put an asLowercase message to the last expression because the keys are case sensitive and via this method the program will be able to find the correct key even if the user enters for example Programming Language 8 In Arrays we have a collection of data which is held in order and accessed by a numbered index In Dictionarys we also have a collection data but not held in any order So one of the reasons might be about the structure we want to use For example we can create a Students object as Array and reach the information of a student by a numbered index like Student at 1 Or we can choose to keep students according to their name via a Dictionary class and reach a student s information
19. loop If we didn t write an argument for block object then we would get an error to by do Sometimes we might not want to increase the index of to do message one by one There is an alternative message called to by do for this purpose Its general structure is like this aNumber to anotherNumber by step do aBlock It allows us to reach the number anotherNumber in steps of the number defined by step For example write the same example above this time by using this alternative message to increase the index two by two Also count until ten this time so that the loop does not end very quickly tobydo st A program to demonstrate the usage of to by do message 1 to 10 by 2 do x Transcript show This is the x printString line cr Controlling the Flow of Execution 51 This is the 1 line This is the 3 line This is the ore limes TArt ther emer This is the 5 line You can see the effect from the output This message can also be used to make counting backwards like tobydo backwards st A program to demonstrate the backward capability of to by do message 5 to 1 by 1 do x Transcript show Oh my god I m counting backwards This is the x printString Linel cr Oh my god I m counting backwards This is the 5 line Oh my god I m counting backwards This is the 4 line Oh my god I m counting backwards This is the 3 line Oh my god I m counting backwards Th
20. man3 womanl woman2 Man new setName Michael Cooper setAge 32 setMoney 9 setHandsomeness 7 Man new setName Paul Anderson setAge 28 setMoney 7 setHandsomeness 8 gt aWoman getHonesty lt aWoman getHonesty aWoman getHonesty 102 Computer Programming with GNU Smalltalk man3 Man new man3 setName Canol G kel man3 setAge 24 man3 setMoney 1 man3 setHandsomeness 1 womanl Woman new womanl setName Louise Stephney womanl setAge 26 womanl setHonesty 6 womanl setGenerosity 7 woman2 Woman new woman2 setName Maria Brooks woman2 setAge 32 woman2 setHonesty 8 woman2 setGenerosity 6 manl gt man2 printNl manl lt man2 printNl man3 gt manl printNl womanl gt woman2 printNl womanl lt woman2 printNl true false true false Erus answer_5_3 st Number extend cubed self self self 3 cubed printNl 2 4 These two keywords are used to refer to the receiver object of the message inside the class definition Whenever we send a message to self or super keyword the interpreter sends the message to the current object in context The difference of super keyword from self is that when we send a message to super the search Answers of Review Questions 103 of the method begins from the superclass of the receiver object So the method inside the superclass is invoked instead of the
21. message is case sensitive Canol includes N false indexOf Sometimes just knowing whether a string includes a character is not enough You also want to know exactly where it is You can use indexOf message to learn it Canol indexOf n 5 If a character is not present in the string then this method returns 0 And if character exists more than one time then it returns the index of the first appearance of that character in the string reverse This is one of my favorite messages in Smalltalk You can reverse a string via reverse message dlrow eht ni remmargorp tseb eht si lonaC reverse Canol is the best programmer in the world Isn t this fun countSubOollectionOccurrencesOf You can count how many occurrences of a certain string are there in another string via countSubCollectionOccurrencesOf message Thomas Edison the inventor of the light bulb was afraid of the dark countSubCollectionOccurrencesOf the 3 34 Computer Programming with GNU Smalltalk If you want to concatenate two strings into one String object you can place a comma character between them Best friends Best friends Actually you can concatenate as many strings as you want via message chaining Best friends should never be separated Best friends should never be separated asUppercase You can convert a whole sentence into uppercase using asUppercase message Hey I m t
22. method of the receiver object s class 104 Computer Programming with GNU Smalltalk Answers of Review Questions 105 Alphabetical Index accessor 66 Argument 20 Assembly assignment 35 assignment operator 35 Binary file 8 Binary message 2 binary number 7 bit 7 Block 45 block argument 46 Blox 83 Blue Book 79 body 60 byte 7 byte code 4 carriage return 24 character encoding 9 character set 9 class 55 Class 24 Class Browser 83 class method 58 class variable 58 command prompt 14 comment 15 compilation 3 compiled language 3 compiler 1 3 Cross platform 5 custom class 58 declaring a variable 60 definite loop 50 encapsulation 55 experienced programmers II expression 15 file format 8 getter 66 GNU Smalltalk I GST 16 GUI 1 3 has a 57 header 60 indefinite loop 48 indent 59 index 37 information hiding 55 instance 24 instance variable 19 interactive mode 4 interpretation 3 interpreted language 3 interpreter 1 3 is a 57 keyword message 2 loops 92 106 Computer Programming with GNU Smalltalk machine code Selective controlling 45 machine language Selector 19 message 13 19 self 72 message cascading 23 setter 66 message chaining 23 single inheritance 58 method 9 single paradigm programming language 6 multi paradigm programming language 5 Smalltalk 80 I multiple inheritance 58 software object 19 source code 4 15 Object oriented programming 5 standard output 4 operato
23. of the numbers so far is Please enter a new number or finish to exit sum sum newNumber asInteger howManyNumbers howManyNumbers 1 arithmeticAverage sum howManyNumbers Transcript cr ls Arithmetic averages of the numbers so Please enter a new number or finish Arithmetic averages of the numbers so Please enter a new number or finish Arithmetic averages of the numbers so Please enter a new number or finish 1 to 1000 do x x printNIl i 1000 i Tes ALEK 10 to exit 2 far ise 2 to exit 4 eue kee 19 to exit finish 1 Polymorphism is the name of the concept to determine which method to execute according to the type of the class of the object we sent the message Observing the attributes and behavior of the ancestor class when deriving a new class from it is Answers of Review Questions 99 called inheritance Encapsulation is hiding the inner working details of an object from outside world answer 5 2 st Object subclass Human name age setName aName name aName getName name setAge anAge age anAge getAge age introduceYourself Transcript show Hello my name is name and I m age printString years old cr aHuman age aHuman getAge aHuman age aHuman getAge aHuman age aHuman getAge Man money handsomeness Human subclass setMoney amountOfMon
24. provides less work when refactoring your application For example our code won t be affected whenever a new property is introduced to the watch class because the changes are automatically reflected to the output by using the super keyword otherwise we would have to copy the changed code into our WaterResistantWatch every time It would be erroneous if we used the se1 keyword instead because it would call itself recursively and this would cause an infinite cycle Also it wouldn t give us the effect we wanted because the code we need is written in superclass definition not in the class we are doing implementation right now In the rest of the program we define two watches which are of Watch and WaterResistantWatch class and list their features after setting their properties As we expected the second watch displayed the properties it inherited from its superclass as well as its special property resistanceDepth Review Questions 1 Explain polymorphism inheritance and encapsulation in a few sentences 2 Now think of symbol as better than and not greater than Create a Man class which inherits from the Human class we created before with additional instance variables money and nandsomeness You know for us men appearance is not important the important thing is the beauty inside So create the Woman class with additional instance variables honesty and generosity All this instance variables will get an integer point over ten Implemen
25. the computer in base 2 like this 00000011 We have written it with 8 digits representing 1 byte of memory Now given the information above try typing the following code 3 bitAt 3 put 1 This expression has an object of number 3 and a message bitAt 3 put 1 We have the selector bitAt put and two arguments 3 and 1 in this message Remember how we get the selector name We get rid of the arguments and put together the rest of the message This message tells the integer object 3 to reach 3th bit of itself and replace it with 1 The bits are numbered from right to left starting from 1 We had 0 at the 3th bit of 3 before But it is now 1 So we have 00000111 which corresponds to 7 at base ten After sending the message the expression is evaluated and printed to the terminal 4 Actually the format the integer is kept in the memory might be a little more complex for optimization purposes but for the example we will give you can rely on this assumption Objects Messages and Classes Part 21 Unary Binary and Keyword Messages There are 3 types of messages The difference between them is about the selectors arguments and the precedence What is precedence It will be explained in a few minutes Unary messages are messages without any argument It is called unary because the resulting expression involves only one object An example for an expression with unary message would be Hello World size As you can se
26. to notice is that interpreted languages require additional steps to be launched and it slows down the execution time Actually there could be both compilers and interpreters for the same language depending on its structure but most languages are designed with one of them in mind so there could be differences between the compiled version and the interpreted version of a language Although the two types of programming languages are much popular in this scene there is also another type which is between this two paradigms This paradigm compiles the source code into an intermediate level which is still not understandable by hardware nor by humans This level of conversion is generally called byte code compilation This process is done so that the code s level is Introduction to Programming World 5 made more close to hardware and converting it to completely understandable form by hardware is much faster The converting process from byte code to machine code is done by programs called virtual machines The thing virtual machines do is interpreting the byte code into machine code when the program is executed by user Why there is this third type of language Because interpretation is slow compared to executing a compiled program but has an advantage of being cross platform Cross platform is the name for being able to run a software on different computer architectures like different operating systems or different processors So you can launch
27. watch has chronometer capabilities After defining the accessor methods for these properties we created another method named listYourFeatures to print out the features of the watch to standard output So far we didn t see anything unusual After defining the Watch class we derived a new class named WaterResistantWatch to represent well water resistant watches We added a new property named resistanceDepth to determine the depth the watch can stand without leaking the water inside Now the tricky part comes we overrode the listYourFeatures method of its superclass and put the line below to the beginning of the method super listYourFeatures This sends the list YourFeatures message to itself but the difference of the keyword super from the keyword se1 is that it will start looking up the definition of the method starting from the ancestor of the class which is the class Watch in this case So the list YourFeatures method of Watch is invoked instead of the List YourFeatures method of WaterResistantWatch class Why do we do this Because Wat ch class already has some of the properties WaterResistantWatch Objects Messages and Classes Part Il 77 has and it already has the capability of listing those features We can either copy and paste the same code into the new listYourFeatures method or we can call the method defined inside the superclass The latter way is preferred by programmers because it reduces the repetition of the code which
28. whileTrue The operator checks if the object on its left is not equal to the object on its right While we progress with different inputs GNU Smalltalk virtual machine gives us the average in a fractional form to do General structure of this message is aNumber to anotherNumber do aBlock 50 Computer Programming with GNU Smalltalk This structure starts from number aNumber and evaluates the aBlock object until it reaches anotherNumber It increases one at every loop aBlock object also includes a block argument so that programmer can use the current index in expressions of aBlock We mentioned that whileTrue message is usually used with indefinite cases to do on the contrary is used when it is known how many loops we needed That s why it is sometimes called definite loop For experienced programmers Being a definite loop you might guess that this message is used in Smalltalk instead of for loop of C based languages Now let s look at this structure via an example 5 lines st A program which prints 5 lines to demonstrate the usage of to do message tos 5 dor 7x Transcript show This is the x printString R line cr Thrs qs the I line This is the 2 line has is the 3 Viner This is the 4 line This 1s the 5 Line This program prints five lines to the output each indicating their own index Note that we used a block argument x for getting the index of each
29. 100 0100 D 100 110 0100 d 5 000 0101 ENQ Enquiry 37 010 0101 69 100 0101 E 101 110 0101 e 6 000 0110 ACK Acknowledgment 38 010 0110 amp 70 100 0110 F 102 110 0110 f 7 000 0111 BEL Bell 39 010 0111 71 100 0111 G 103 110 0111 g 8 000 1000 BS Backspace 40 010 1000 72 100 1000 H 104 110 1000 h 9 000 1001 HT Horizontal Tab 41 010 1001 73 100 1001 I 105 110 1001 i 10 000 1010 LF Line Feed 42 010 1010 74 100 1010 J 106 110 1010 j 11 000 1011 VT Vertical Tab 43 010 1011 75 100 1011 K 107 110 1011 k 12 000 1100 FF Form Feed 44 010 1100 76 100 1100 L 108 110 1100 t 13 000 1101 CR Carriage Return 45 010 1101 z 77 100 1101 M 109 110 1101 m 14 000 1110 SO Shift Out 46 010 1110 78 100 1110 N 110 110 1110 n 15 000 1111 SI Shift In 47 010 1111 79 100 1111 0 111 110 1111 o 16 001 0000 DLE B 48 011 0000 0 80 101 0000 P 112 111 0000 p 17 001 0001 Del is Control 49 911 0001 1 81 101 0001 Q 113 111 0001 q 18 001 0010 bee ONES Control so 911 0010 2 82 101 0010 R 114 111 0010 r 19 001 0011 DES texire Control 51 911 0011 3 83 101 0011 s 115 111 0011 s 20 001 0100 DCA evite Control 52 911 0100 4 84 101 0100 T 116 111 0100 t NAK Negative 21 001 0101 Kee men 53 011 0101 5 85 101 0101 U 117 111 0101 u 22 001 0110 SYN Rd Pneus 54 011 0110 6 86 101 0110 v 118 111 0110 v ETB End of 2
30. 3 001 0111 Transmission Block 55 622 6211 7 87 101 0111 w 119 111 0111 w 24 001 1000 CAN Cancel 56 011 1000 8 88 101 1000 x 120 111 1000 x 25 001 1001 EM End of Medium 57 011 1001 9 89 101 1001 Y 121 111 1001 y 26 001 1010 SUB Substitute 58 011 1010 90 101 1010 z 122 111 1010 z 27 001 1011 ESC Escape 59 011 1011 91 101 1011 123 111 1011 t 28 001 1100 FS File Separator 60 011 1100 lt 92 101 1100 124 111 1100 29 001 1101 GS Group Separator 61 011 1101 93 101 1101 125 111 1101 30 001 1110 RS Record Separator 62 011 1110 gt 94 101 1110 126 111 1110 x 31 001 1111 US Unit Separator 63 011 1111 95 101 1111 127 111 1111 Delete 88 Computer Programming with GNU Smalltalk Answers of Review Questions 89 Appendix C Answers of Review Questions Chapter 1 1 Because of the hardware design computers can only understand two states We represent this two states with digits 0 and 1 Combinations of zeros and ones generate some commands that computer hardware understands We call these command groups which provide a communication between us and computer hardware as programming language We need them to communicate with computer hardware because computer hardware can understand only two states and the programming language we use is eventually translated into the sum of combinations of this two states which is called mach
31. Computer Programming using GNU Smalltalk Canol Gokel Last updated 4 10 2009 Cover photo by Tibor Fazakas over www sxc hu Content on this book is licensed under a Creative Commons Attribution 3 0 cc License or at your choice under the GNU Free Documentation License 1 3 BY with no invariant sections front cover texts or back cover texts To the ant I accidentally crushed yesterday Canol G kel Preface Computers are machines composed of hardware and software written for the hardware Whether you are an amateur user who uses his her computer just to surf the Internet or an average user who uses computer for daily tasks you may need to write a program for a specific duty Maybe you are just a curious user who wants to dominate the box in front of him before it starts dominating you Programming is the key word here because you make the computer do what you want by programming it Programming is like putting the soul inside a body This book intends to teach you the basics of programming using GNU Smalltalk programming language GNU Smalltalk is an implementation of the Smalltalk 80 programming language and Smalltalk family is in general a little bit different than other common programming languages like C or Java So we will apply a different approach to teach you programming compared to other computer programming books out there You will see chapters of this book are mostly short compared to other programming b
32. E AE NEE a r A E ANT E AEA EEA 42 Chapter 4 Controlling the Flow of Execution 45 VI BLOCKS mm 45 Selective Controlling T N 46 Repetitive Controlling eset niee n n i Pee EXE ere En ELE E Re dee EEE hE EENE ERENER 48 Review QUESTIONS orsono inanin ees a aan E AE GE EO Ea 51 Chapter 5 Objects Messages and Classes Part I 55 Encapsulation T M M 55 TOS E E NEA 55 Folymorphism eee eto Sek Ai owls eae TG ses eae vias ER rit PD pU QR qe 58 Creating Your Own CLASSES Em 58 Creating Objects From Classes 1 ccs ek besten tret tnr eco toga nee eoe via REES 62 AYUDE M 63 Extending and Modifying Classes esses eene nennen nennen rennen entren nnne 67 self ONG SUPET veces e vnnnn M H 72 REVIEW QUeSTIONS i visecsascaezevsaseied M TI Chapter 6 What to Do Next 79 How Can I Improve Myself esee esent nennen nere nenne teen eeet eset aaie 79 Further Reddine R 79 Useful Sites iate negoti pote e E HU P E RU EARE 79 Int M 80 js M 80 Appendix A Installing Programming Environment 83 Installing GNU Smalltalk on Linux Platforms eese eene nennen 83 Installin
33. Messages and Classes Part 29 GST can also calculate negative powers of a number by returning nice fractional numbers 3 raisedTo 2 LY squared We can find out the square of a number by using squared message instead of using raisedTo 2 3 squared 9 even We can determine if a number is even or not by using the even message 4 even CEUS 2222222221 even false odd And we can test if a number is odd or not by using the odd message 3 odd Erue sign sign message returns 1 if the number is positive and 1 if the number is negative 6 sign Now we will see some messages you can use with floating point numbers integerPart integerPart message gives us the integer part of a floating point number 0 7 integerPart 30 Computer Programming with GNU Smalltalk 0 0 3 1 integerPart Sa truncated To truncate a decimal number we use t runcated message 17 2 truncated 17 Note that this is not rounding 17 6 truncated 1g To round decimal numbers we use rounded rounded message 17 6 rounded 18 Let us see some messages special to fractional numbers denominator To get the denominator of a fractional number we use denominator message 3 4 denominator 3 Notice that we parenthesized the expression 3 4 The reason is that if we didn t do that then the unary message denominator Would be calculated before the expression 3 4 because as we said before unary messages are
34. N1 message on a string object For example this time there are no single quotes around our output Also there is no new line after the output We will show you how to put a newline character at the end of the output when using Transcript in the Message Cascading section just a few minutes later Lastly the output is printed only once while it was printed twice every time we used printN1 message This is because the overall object returned is the Transcript itself and it does not have a representation as a string Message Chaining If you write more than one message next to an object name all messages will be sent to the resulting object of the preceding message This is called message chaining The general syntax for message chaining is like this objectName messagel message2 message3 messageN So while messagel1 is sent directly to ob jectName message2 is sent to the resulting object of expression objectName messagel Using the same logic we can say that message3 is sent to the resulting object of expression objectName messagel message2 Here is a real life example of message chaining Canol reverse asUppercase LONAC We manipulated the string Cano1 multiple times with two messages to reach the resulting string object LONAC Message Cascading GNU Smalltalk allows us to send multiple messages to an object without writing object s name over and over This is called message cascading The general syntax for m
35. NU Smalltalk false 3 isAlphaNumeric true You might need such methods when you expect some input from user for example Since you cannot know what a person might enter as data you should use this kind of methods to ensure that data entered is in a valid format isDigit Maybe you just want to determine if a symbol is a digit 4 isDigit true c isDigit false isLetter Or you might be interested in whether the data is a letter or not c isLetter teue 4 isLetter false String Strings are object compound of several character objects We use strings to represent words sentences paragraphs etc To tell Smalltalk environment that we are creating a string we put single quote character before and after a sequence of characters For example Canol I want a cup of coffee are all string objects We use two single quote character consecutively to represent a single quote character in a string Eiffel Tower s height varies as much as six inches depending on the temperature Note that it is two single quote and not a double quote Objects Messages and Classes Part 33 Since strings are used by programmers heavily we have a lot of useful methods for them Below are some messages I selected Editor s Choice Awards go to includes If you wonder whether a string object includes a specific character object in it you can use includes message Canol includes n Erue Note that this
36. This Book for This book assumes that the reader does not have any experience with programming but does have experience with using the computer meaning how to open close it how to run programs how to save files etc For experienced programmers II We will often use this kind of box to speak to experienced programmers referring a person who has knowledge of another programming language than Smalltalk Newcomers do not have to read the contents of this box For experienced programmers This book can also be used by experienced programmers Actually this book is the one you should read because most probably GNU Smalltalk is pretty different than what you have seen so far and this book teaches you Smalltalk as if it is your first programming language How to Use This Book If you are an absolute beginner then we suggest you to read the chapters in order and look at the appendixes anytime they are referred We tried to write this book in an order that you won t need to look at a future chapter because of unseen concepts so you may need to turn a lot of pages to look at appendixes but not for anything in the main text We tried to keep the examples as simple as possible so that they won t confuse you with unnecessary details and just demonstrate the concept in discussion During the learning process of a programming language it is very important to practice the theoretical subjects you learned We t
37. alking to you asUppercase HEY I M TALKING TO you And you can use asLowercase message to lowercase your sentence though we won t give an example for that size You can learn how many characters a string has by sending it the size message There are 39 characters in this string size 39 Variables Variables in Smalltalk is a lot like variables we use in mathematics You may keep that in mind while reading this topic to imagine this concept easier While writing a program we will have a lot of objects They will be created manipulated and destroyed But after creating an object how can we refer to it at any place in our program Suppose that we have a Human class not a class provided by the standard library of GNU Smalltalk but an imaginary one and we create new instances from it Like humans in our world they need a name so that we can communicate with them Remember that we communicate with objects via sending messages to them and before message we should reach that object to specify which object we want to be the receiver This can be achieved with an expression which returns the object or referring the name of the object Suppose we have a Human instance named Car1 We can send him a message like Objects Messages and Classes Part 35 Carl tellUsYourLastName Here Carl refers to a Human instance Giving a name to an object is called assignment and we call this names variables in programming jargon
38. alled the header of the class The part between the square brackets is called the body of the class The names we put between pipes are instance variables of our class instanceVariablel instanceVariable2 Instance variable names are separated by white spaces We have two instance variable here named instanceVariablel and instanceVariable2 Then we define class variables by using assignment syntax classVariablel anObject classVariable2 anotherObject is another message which makes the receiver an object referring to the argument object So whenever we use classVariablel in our code from now on the interpreter will understand that we are actually referring to the anObject object We will use this assignment message also for changing the instance variables Mentioning about a variable for the first time is called declaring a variable We should first declare a variable before being able to use it Next expression adds a comment to the class Objects Messages and Classes Part l 61 comment Comment to describe our class gt They are only for documentation purposes and appear on IDEs we use for explaining what a class or method does so that we can get an idea of what it does without looking at its code which would took much longer and be harder They do not affect the execution of the program so we can omit them And the time comes to defining the class and instance methods We first created a class method
39. am which involves a block with an argument greetings greetings platesOfCornFlakes I have eaten platesOfCornFlakes printString plates of corn flakes this morning Hello ma greetings value 3 printNl Hello ma I have eaten 3 plates of corn flakes this morning Here we first created a variable named greetings to hold a block we will create Then we created a block object with an argument and assigned it to the variable Note that when we used the argument inside the expressions we didn t write the preceding colon It is only written in declaration time and then omitted Finally we used this block with an expression greetings value 3 Don t forget to parenthesize the necessary groups for the sake of the precedence rules Now we are ready to go on with controlling expressions Selective Controlling ifTrue Our first selective control message is ifTrue lts general structure is like this Controlling the Flow of Execution 47 anObject ifTrue block expression 1 block expression 2 When it is sent to a Boolean object it executes the expressions inside the code block if it is true ignores if it is false Let s give an example ourVariable ourVariable true ourVariable ifTrue Our variable is true printNl Our variable is true We first created a variable called ourVariable and then set it as a true object Then sent it a ifTrue message Because ourVariable is s
40. ays asks user to enter a new number and calculates the arithmetic average of numbers entered that far by using either definite or indefinite loop technique If the user wants to finish entering new numbers she should enter the string finish 9 Now can you write the one line program mentioned in Review Question 4 in Chapter 2 Controlling the Flow of Execution 53 54 Computer Programming with GNU Smalltalk My brain it s my second favorite organ Woody Allen Objects Messages and Classes Part ll 55 Chapter 5 Objects Messages and Classes Part II Encapsulation Ever wondered how the electronic circuits inside your cell phone works Ever needed to know that Most probably not Because we don t need to know all the manufacturing details about our cell phone to use it Just reading the manual is enough to use all of its features So we cannot know all details all scientific laws all properties of an object we use and we don t need to Object oriented programming introduces encapsulation concept to apply this real life fact in our applications Smalltalk does not allow you to directly modify internal state of an object Objects can only be communicated by sending messages to them So Smalltalk encapsulates the unnecessary information Beside encapsulation allows us to think in a real world manner it also provides some kind of information hiding which helps our program to be solid and reusable This means if you hide an o
41. bility significantly by solving a few of these problems Also you can contribute to improve the rank of the Smalltalk language Smalltalk Jobs http smalltalkjobs dabbledb com If you are searching for jobs related with Smalltalk language then you can look at this page to get one Mailing Lists IRC Mailing lists are a great way to reach as many people as possible regarding to your problems suggestions thoughts Just send an email to the mailing list and everybody who subscribed to the list will get your message and be able to reply You can go http smalltalk gnu org community ml to get more information about how to subscribe to the mailing list or to search previously posted messages The fastest way to get help from GNU Smalltalk community is to ask your question at IRC Internet Relay Chat The address for GST in IRC world is gnu smalltalk channel at irc freenode net You can use an IRC client like XChat on Linux or mIRC on Windows to connect to this channel What to Do Next 81 82 Computer Programming with GNU Smalltalk Wait a minute Pope Alexander VI Last words of him Installing Programming Environment 83 Appendix A Installing Programming Environment At the time of writing GNU Smalltalk was distributed mostly via its source code That means you download the source code of GNU Smalltalk compile it and use it If you are lucky then you might have a binary distribution for your operating system We w
42. binary messages count at put and removeKey as keyword messages We can deal with natural numbers like 3 10 25 real numbers like 3 5 8 2 0 4e5 or fractions like 4 7 8 13 25 138 answer 3 5 st theNumber Transcript show Please enter a number to get its cube theNumber stdin nextLine Transcript show The cube of theNumber is theNumber asInteger Squared theNumber asInteger printString cr Please enter a number to get its cube 3 The cube of 3 is 27 answer 3 6 st theNumbers arithmeticAverage Transcript show Please enter two numbers separated by space to get their arithmetic average theNumbers stdin nextLine tokenize arithmeticAverage theNumbers at 1 asInteger theNumbers at 2 asInteger 2 Transcript show The arithmetic average of theNumbers at 1 and theNumbers at 2 is arithmeticAverage printString cr Please enter two numbers separated by space to get their arithmetic average 10 20 The arithmetic average of 10 and 20 is 15 answer 3 7 st definitions theWord 94 Computer Programming with GNU Smalltalk definitions Dictionary new definitions at programming language put We call the command groups which provide a communication between us and computer hardware as programming languages definitions at source code put The code we wrote in a programming language not the result of a compilation or
43. bject s implementation from the programmer and provide him her just a protocol to communicate with that object then the programmer won t be affected by implementation changes made in the future as long as the protocol is preserved For example you created a Calculator class which is able to calculate the roots of a second degree equation You just send the equation s information to it and it returns the roots Maybe it uses an inefficient algorithm which causes it to calculate the roots in hours But well it is better than nothing and you distributed the code to friends we shall call them clients Maybe after distribution you found a revolutionary approach which reduces the calculation time into seconds The algorithm is changed but the protocol does not need to because the clients just need to provide the equality to the calculator and want it to solve the equation How calculator solves the equation is not their business So you can benefit the advantages of encapsulation and distribute your new code to clients Clients just need to replace the Calculator class and does not need to change their own program Inheritance Human beings like categorizing things Because categorizing brings order and order brings easy manipulation Similar elements come together to form groups or categories and some special properties of them are the thing which distinguishes them from other group members We may group some groups together according to their sim
44. by writing Student at Canol G kel An other reason might about the performance Arrays keep their data consecutively inside the computer memory and the access time for an individual element is always the same while in Dictionarys the time increases as the element size increases Though it is not a significant increase for not too big Dictionarys Chapter 4 1 The ultimate goal of control messages is to give the user opportunity to change the flow of the program instructions Otherwise we won t be able to make decisions or execute a part of the program more than once There are two types of control messages selective and repetitive ifTrue and ifFalse are Answers of Review Questions 95 examples of selective control messages while whileTrue and to do are examples of repetitive control messages Blocks are groups of expressions which we can pass to control messages They are one of the things that make it possible to have control messages Definite loops are loops we know how many times it will repeat itself The end of indefinite loops however depends on a certain condition to occur to do is an example of definite loop messages while whileTrue is an example of indefinite loops answer 4 4 st theLength Transcript show Please enter the length of the edge of the diamond t heLength stdin nextLine asInteger 1 to theLength do x to theLength x do y Transcript show Transcript sh
45. ceYourself myFriend introduceYourself me gt myFriend printNl Hello my name is Canol G kel and I m 24 years old I am an Engineer Hello my name is ismail Arslan and I m 23 years old I am an Engineer false We have done a lot of things let s look at them one by one The first thing we did was adding two new instance variables named occupat ion and experience to keep the occupation of the human and its experience on the job occupation experience Then we wrote the accessor methods for these new instance variables getOccupation occupation setOccupation anOccupation occupation anOccupation getExperience experience setExperience anExperience experience anExperience Because these accessors are not written before they are added to the class behavior We then rewrote some methods introduceYourself Transcript show Hello my name is name and I m age 72 Computer Programming with GNU Smalltalk printString years old I am occupation se UE aHuman experience aHuman getExperience aHuman experience aHuman getExperience aHuman experience aHuman getExperience They have overridden the old implementations New introduction method includes the occupation of the Human We also changed the comparison methods so that the comparison is being made according to the experiences of the Human objects this time This chang
46. ches setResistanceDepth aDepth A method to set the resistance depth of the watch resistanceDepth aDepth getResistanceDepth A method to get the resistance depth of the watch resistanceDepth listYourFeatures A method to print out the features of the water resistant watch super listYourFeatures Transcript show Resistance depth self getResistanceDepth printString watchl watch2 watchl Watch new watchl setStyle Analog watchl setChronometerCapability true 76 Computer Programming with GNU Smalltalk watch2 WaterResistantWatch new watch2 setStyle Digital watch2 setChronometerCapability false watch2 setResistanceDepth 30 Transcript show The features of the lst watch cr Transcript shows cec c ocoooes p OKs watchl listYourFeatures Transcript cr Transcript show The features of the 2nd watch cr Transcript show Y c Mn Iii eiie ipie P Or watch2 listYourFeatures The features of the 1st watch Style Analog Chronometer capabilities true The features of the 2nd watch Style Digital Chronometer capabilities false Resistance depth 30 In this program we started by defining a class named wat ch to represent ordinary watches It has some properties like style which determines whether the watch is analog or digital and chronometerCapability which determines whether the
47. conds So today we cannot think some of the areas without getting help of computers For example military hardware should be fast to be able to do thousands of complex calculations in very limited time accurately Or some science branches like astronomy require to make calculations which are almost impossible to do with paper and pencil Smalltalk is not an exceptional language for this kind of purposes We will now see the most commonly used messages to create repetitive expressions whileTrue The general structure of this message is like this aBlock whileTrue anotherBlock This message is designed to be sent to block objects When it is sent the receiver block object is evaluated and if the evaluated value is to be a true object then the block sent as the argument is executed Up to this point it is very much like an ifTrue message except that it is sent to a block object not directly to a Boolean object But the main difference appears from this point on If the receiver object evaluated to true and the argument block is executed then the receiver block is controlled once more If it still evaluates to true then the argument block is executed once more This cycle will be run until the receiver block evaluates to false While loops are called indefinite loops because generally it is not known how many times the loop will be executed If it is known then you should consider checking your design again because most probably the upco
48. cript show Hello my name is name and I m age Objects Messages and Classes Part ll 69 printString years old cr aHuman age aHuman getAge aHuman age aHuman getAge aHuman age aHuman getAge me myBrother me Human new me setName Canol G kel me setAge 24 myBrother Human new myBrother setName G rol G kel myBrother setAge 27 me introduceYourself myBrother introduceYourself me lt myBrother printNl Hello my name is Canol G kel and I m 24 years old Hello my name is G rol G kel and I m 27 years old Erue Our Human class is pretty simple It has two instance variables named name and age After defining the accessors setName getName etc we defined a method named introduceYourself When a Human object is sent this message it introduces itself by telling some information about itself We have also written methods to compare two Human s age If a comparison is wanted to be done among two Human objects you can use gt lt or binary messages Notice that we have used the instance variable age for the receiver and sent the getAge message to the argument object to reach the ages of them which are integer numbers The comparison methods are already defined for Integer objects so we don t have to go deeper This implementation is pretty simple Suppose that we needed to add a few more details to this class We can
49. cters and not funny symbols all around it is most probably a text file Also some text editors might detect that a file is not written in a recognized text encoding and warn the user about it Text editors are designed only to work with text files while word processors have most probably have their own binary file format to save documents Like doc for Microsoft Word and odt for OpenOffice org Writer Word processors have a lot of fancy formatting tools to write a text in bold italic colored etc which we don t use when writing text files Most word processors have options to work with text files but they have so much unnecessary features we won t use that using them is like using a limousine to harvest Chapter 2 1 answer_2_1 st Transcript show X Th ers Transcript show er Transcript show Xs Or Transcript show pre GES Transcript show cr Transcript show N T cr UN l N o 2 When we have a small task to complete or when we are experimenting things using terminal to enter the program instructions is very practical But if we have to write a big program saving it to hard disk by writing its source code into a text file will make it easy for us to work on it later on Also saving the source code provides us the opportunity to use that program again whenever we want Comments provide the reader of the source code additional information so that he she understands the code fa
50. d Classes Part 37 above lines respectively you should have got an output like above It shows the current state of our Array object At first all of the objects of an Array object are initialized as nil object which is a special object to represent nothing at To get a single object at a certain position we can use at message Please keep entering the commands like we write here anArray at 1 joist th We get the first object in our array which is of course the nil object The positions of an array are called indexes In Smalltalk indexes begin with the number 1 For experienced programmers In contrast to C based languages in Smalltalk indexes begin with 1 not with 0 at put To place an object to a certain position we use at put message anArray at 1 put Toothbrush U Toothbru sh We can see what the objects in our array are by simply writing its name anArray Virersitelnonetwsin orl pil mil fiL pil nil mir pil pil As you can see now the first object in our array is the String instance Toothbrush Let s put a soap to our array anArray at 2 put Soap Soap anArray Yr ornerbisiaY SCA pa sev ih sot ill soi th joynil yoy ih yout il joy ik 3ewtiL 3 includes We can investigate if an array has a certain object in it by sending it the includes message along with the object we are searching anArray includes Soap 38 Computer Programming with GNU
51. dd anElement Perfume aSet Set Soap Toothbrush Perfume Let s remove it aSet remove anElement Perfume aSet See Soap ia Toothbrush j Now it is removed from the Set let s control whether our variable is still alive anElement Perfume As you see it is still alive and well The remove message we sent to the Set didn t affect our variable and the St ring object it points Dictionary The last class we are going to show you is called Dictionary Dictionarys again provide a way to group a bunch of objects together like Arrays and Sets Dictionarys are like Arrays in that they keep their data associated with an index key but the difference is that the keys don t have to be numbers You can define any object as a key for a data And Dictionarys are like Sets in that they don t keep their data in any order and they don t have a predefined limitation how much object you can keep in it Objects Messages and Classes Part 41 new We create a dictionary with new message just like Sets aDictionary aDictionary Dictionary new Dictionary The output shows us that initially our Dictionary does not contain any object in it at put We can add an object into a dictionary by using at put message aDictionary at Canol put Gokel Gokel aDictionary Dictionary Canol Gokel Our dictionary now holds a string named Goke1 associated with another string named Canol
52. e level depends to the programmer A programmer may choose as many spaces or tabs to insert as she wants for indenting a line but the important thing is to be consistent throughout the program so that 60 Computer Programming with GNU Smalltalk it does not look messed up Other than the indentation also most of the white spaces we used were programmer dependent You can choose not to place or even place more white spaces around anything If it is a wrong usage whenever it causes an ambiguity then the interpreter will give you an error For example you cannot join the variable name and a keyword selector because interpreter cannot detect where the variable name ends and where the keyword selector begins So you should put at least one space there Let s look at the code above line by line The first thing we do is to define a class with the code piece below SuperclassName subclass SubclassName The three dots in our code always mean that there are more expressions there but we cut it short to emphasize the really important part So you should not put three dots in your code With the part above we told SuperclassName class to create a subclass named SubclassName We did this to inherit the properties and behavior of the superclass so we don t have to create them again After doing that we opened a bracket to specify the class variables instance variables class methods and instance methods The part up to the opened bracket is c
53. e meaningful code Outputs results of complete programs are given with a purple background like this Output of a program The input part of a program which is entered by user while the program is running are showed in bold face at the output Please enter your name Canol When we mention about keys on your keyboard we ll write them between angle brackets like lt CTRL gt Enter or Backspace We also have some special boxes Note This kind of boxes contain important details some additional information or suggestions For experienced programmers This kind of boxes contain some hints for people who knows some other language but reading this book to learn GNU Smalltalk Beginner users or even experienced programmers don t have to read or understand things written in this boxes Question This kind of boxes contain some special questions which are answered at the and of its chapter 1 We will use Enter throughout the book for both Enter key on PCs and the Return key on Macintosh computers IV Contents Preface Who is 1 his Book for etit dr e caved e ee as ree RR CER AE EROR Le CE RERS I How to Use This BOOK tete ett tet eeto eei ivt a eese tiec e p vero b ese be SEE Ee E REESE CORPUS TS II FONE ET DVADIMREREERERERNRI M II Chapter 1 Introduction to Programming World 1 What is Programming and What are Programm
54. e there are no arguments here and the overall expression involves only the string object Hello World Binary messages are messages with an argument But the other characteristic of binary messages is that their selectors have up to 2 characters which are not alphanumeric An example for an expression with binary message would be 3 4 is a selector here and 4 is the argument for it The expression involves two integer objects of 3 and 4 is one character long and it is not an alphanumeric character So it meets the requirements of being called as a binary message Finally keyword messages are messages with one or more arguments whose selectors are composed of alphanumeric characters They usually have a colon at the end of each selector word which indicates that it is demanding an argument An example for an expression with keyword message would be 3 bitAt 3 put 1 Our selector here is bitAt put where our arguments are 3 and 1 Overall expression involves three objects but it could have been one or two or another number greater than three We gave the selector and argument features of message types but we didn t mention about precedence of them Precedence is a concept used for deciding which one of the messages will be executed first if there are many messages in one expression If you cannot imagine an expression with many messages don t worry here it is 3 5 bitAt 3 put 1 printNl As you might see here are three m
55. ed as we write that is line by line or more correctly statement by statement then this process is named as interpretation and such languages are called interpreted languages Software written in interpreted languages are kept in computer memory as the way we write them and every time we execute or launch run them they are interpreted again into machine language The software doing the interpretation process is called interpreter 4 Computer Programming with GNU Smalltalk The code we wrote in a programming language not the result of a compilation or interpretation process is called source code Hello Hello World World Source Code Compiler interpreter Compilation Interpretation Process 11000010 11000010 10001010 10001010 10010101 10010101 Machine Code 01111011 01111011 00100110 00100110 The figure above demonstrates the difference between launching a compiled program and an interpreted program A user can reach directly to the compiled program which is kept as machine code in computer memory while she can reach only the source code of an interpreted language The system then recognizes the file format and sends it to the interpreter to interpret it into machine code Sometimes the system may not be able to recognize the file format and we might need to send the file to the interpreter manually The main thing
56. ed value like this Hello World printNl 3 7 printNl value THel lo World 10 10 Note that the object 10 is printed twice because the last expression is returned as the result of the block which is the object 10 Again this is only the case when you are entering the codes above interactively 46 Computer Programming with GNU Smalltalk via terminal As we will see in control expressions blocks are very useful object structures But before going on with control expressions we should also mention about a feature of blocks block arguments Sometimes blocks may need additional data to evaluate the codes in it We can then create one or more block arguments to pass as many additional data as we want The general structure of a block with arguments is blockArgumentl blockArgument2 block expression 1 block expression 2 The block arguments are at the beginning of a block and every argument is declared with a preceding colon Then the argument part of the block is separated from the main content via a pipe character We will mostly use this kind of blocks with special messages which know how to use them But if you ever need to use such a block manually then you should send it a message whose selector includes as many value as the argument number For example for a block with three arguments you should use the selector value value value Let s finish this subject with an example program blocks st A progr
57. ent at real life but a huge reason of why programming languages are present For example you may want to do something thousands of times The first sample that comes to our minds is mathematical problems Consider we want to find all the prime numbers up to 100 billion Trying this on paper with a pencil is obviously not good for your health Instead we develop an algorithm to find whether a number is prime or not and then apply it on all the numbers from 1 to 100 billion Thanks to the hardware capabilities today we can find the solution of such problems in milliseconds and importantly without a mistake So we divide controlling into two main types Selective and repetitive Selective controlling selects a part of our code to be executed according to a condition decision And repetitive controlling will allow us to execute a part of the code over and over Before going on with how to do selective or repetitive controlling with GNU Smalltalk we will see a concept named block which we will extensively use along with controlling messages Blocks Blocks are objects to bring together some expressions and hold them together for later use They are nothing but a series of code written between square brackets This is an example of a block Hello World printNl 3 7 printNl The key things are to remember that blocks are also objects and when you create a block the code in it won t be executed right away You should send it a message nam
58. es sound like they are made by an employment agency which uses Human class inside their applications self and super It is time to learn two new keywords of GNU Smalltalk The purposes of these two keywords we will see in a few seconds are the same referring to the receiver object of the message while writing the class definition The difference becomes apparent when we try to invoke a method on the referred object self The first keyword to see is self When we use this keyword in a class definition it is treated as the receiver object For example we could define the basic Human class like this human self st The second version of the Human class written using self keywords Object subclass Human name age setName aName name aName getName name setAge anAge age anAge Objects Messages and Classes Part ll 73 getAge age introduceYourself Transcript show Hello my name is self getName and I m self getAge printString years old cr aHuman self getAge aHuman getAge aHuman self getAge aHuman getAge aHuman self getAge aHuman getAge me myBrother me Human new me setName Canol G kel me setAge 24 myBrother Human new myBrother setName G rol G kel myBrother setAge 27 me introduceYourself myBrother introduceYourself me myBrother printNl Hello my name is Canol G kel and
59. essage cascading is as follows objectName messagel message2 message3 messageN 24 Computer Programming with GNU Smalltalk We put semicolon between the messages we want to send Beware that this is different than message chaining in which semicolons are absent and every message is sent to the resulting object of preceding message Here is an example for message cascading Transcript show Canol cr cr is a message which causes Transcript to put a newline character which is also called carriage return So we first sent the message show Canol and then the message cr to the Transcript You have to be careful when using message cascading because sometimes precedence rules may cause results that you don t expect Classes Classes may be summarized as the templates of the objects we want to create We first define a class then produce objects from it That s why objects are also called instances of their classes It is like the blue print of houses Every object has a class related to it For example Hello World object is created from the String class or numbers like 2 or 3 are created from a class called SmalliInteger We will mention about the theory of classes later on Chapter 5 in more detail We can think of the blue print as a House class and the actual houses as the instances of it Objects Messages and Classes Part 25 Common Classes and Their Usage Part GNU Smalltalk has a library w
60. essages bitAt put and printN1 Which one should be evaluated first It depends on precedence rules There are some basic rules for message precedence in Smalltalk they are 1 Unary messages are evaluated first 2 Binary messages are evaluated second 22 Computer Programming with GNU Smalltalk 3 Keyword messages are evaluated last 4 If you encapsulate an expression between parenthesis then it is evaluated first 5 If the messages have the same precedence then the messages are executed from left to right respectively Now we will give two examples to illustrate this precedence rules The first one is the above example we have given 3 5 bitAt 3 put 1 printNl 1L lg Now we will investigate why the output is 1 and 12 When our interpreter first meets with this expression it sees the unary message printN1 and executes it with the object in front of it which is 1 So the first output is 1 Then this expression evaluates 1 itself and returns it Our expression turns into something like this 3 5 bitAt 3 put 1 We have two messages here One of them is which is a unary message and the other one is bitAt put Which is a keyword message According to the rules above the expression with binary message will be evaluated first which yields the integer 8 So our expression turned into 8 bitAt 3 put 1 Now we have only 1 message which is a keyword message and it evaluates to integer 12 You can try to do that
61. et as t rue it executed the code block Question Please try the same code with ourVariable is set as false object ifFalse ifFalse message is the same with ifTrue message except that its code block is executed if the object refers to a false object ifTrue ifFalse There will be times that you want to do something if your object is true and want to do something else if it is false This message gives you the opportunity to do that in an easy way The general structure is like this anObject ifTrue block expression 1 block expression 2 ifFalse block expression 3 block expression 4 Of course nothing can stop you if you want to write it in a better looking shape like an object ifTrue the code block to execute ifFalse the code block to execute We will finish the selective control messages by giving an example for ifTrue ifFalse message Here it is 48 Computer Programming with GNU Smalltalk ourVariable ourVariable false ourVariable ifTrue Our variable is true printNl ifFalse Our variable is false printNl Our variable is false Repetitive Controlling Time has come to learn one of the main reasons to use programming languages or machines Because machines do not get tired or do not make mistakes we can order them to do the same thing millions of times and they won t only fulfill they will fulfill it also very fast mostly in millise
62. evaluated before binary messages numerator We use numerator message to get the numerator of a fractional number 3 4 numerator 4 Objects Messages and Classes Part 31 setNumerator setDenominator To set the numerator and the denominator of a fraction we use setNumerator setDenominator message 3 4 setNumerator 5 setDenominator 6 5 6 Note that this time we didn t need to use parenthesis because this time we send a keyword message to the expression 3 4 and binary messages already have a precedence over keyword messages Character Characters are the single symbols we use to represent data For example letters special characters like and digits like 9 are all characters They are individual objects in Smalltalk Though to tell Smalltalk environment that we want to treat a symbol as a character we have to put a dollar sign in front of it For example Sa oe 9 And we use the same methodology to represent dollar sign itself 8 We have a lot of methods to apply on characters some of which are mentioned below asLowercase If you have a letter to convert into lowercase then you can use asLowercase message D asLowercase d asUppercase Uppercase counterpart of asLowercase IS asUppercase d asUppercase D isAlphaNumeric If you have a suspicion whether a symbol is alphanumeric then you can use isAlphaNumeric message isAlphaNumeric 32 Computer Programming with G
63. ext editors to create and manipulate our text files Most of them are specialized for different character sets and encoding On Linux you can use Gedit on Gnome Mousepad on Xfce or Kate on KDE There are also some advanced text editors like Vim or Emacs On Windows you can use Notepad but Notepad is awfully less advanced so you can download a little more advanced ones like Notepad2 or EditPad Lite Using a search engine like Google or Yahoo with keywords text editor will always give you good results A programmer usually needs some others programs during coding compiling and testing of programs Instead of installing and using separate programs you can use programs called integrated development environment IDE which include almost all the necessary things for you Some of the well known IDEs are Anjuta or KDevelop for Linux Microsoft Visual Studio for Windows or cross platform ones like Eclipse and Komodo We won t use such environments because it is not necessary when you are just at the beginning of learning how to program In the next chapter we will be introduced to some fundamental concepts of GNU Smalltalk programming language and write our first program Review Questions 1 What is a programming language why do we need it 2 Explain briefly the differences between compiled and interpreted programming languages What are the advantages and disadvantages of them How can we classify GNU Smalltalk in this manner 3 What are
64. ey 100 Computer Programming with GNU Smalltalk Amount of money out of 10 money amountOfMoney getMoney money setHandsomeness rateOfHandsomeness Handsomeness rate out of 10 handsomeness rateOfHandsomeness getHandsomeness handsomeness gt aMan self getName Canol G kel ifTrue true ifFalse self getMoney self getHandsomeness gt aMan getMoney aMan getHandsomeness lt aMan self getName Canol G kel ifTrue false ifFalse self getMoney self getHandsomeness lt aMan getMoney aMan getHandsomeness aMan self getName Canol G kel ifTrue false ifFalse self getMoney self getHandsomeness aMan getMoney aMan getHandsomeness Human subclass Woman honesty generosity Answers of Review Questions 101 setHonesty rateOfHonesty Honesty rate out of 10 honesty rateOfHonesty getHonesty honesty setGenerosity rateOfGenerosity Generosity rate out of 10 generosity rateOfGenerosity getGenerosity generosity gt aWoman self getHonesty self getGenerosity aWoman getGenerosity lt aWoman self getHonesty self getGenerosity aWoman getGenerosity aWoman self getHonesty self getGenerosity aWoman getGenerosity ma manl manl manl manl manl man2 man2 man2 man2 man2 nl man2
65. g GNU Smalltalk on Windows Platforms eese nennen 85 Appendix B ASCII Table 87 Appendix C Answers of Review Questions 89 eru PH 89 Chapter M 91 Chapter M 92 Chapter MP 94 977 dE 98 VII Postface 107 About the AUTOM 5i eec ec ea b eee tub epe decorus ehe ca reote be ee ees tbe 107 The Star Trek computer doesn t seem that interesting They ask it random questions it thinks for a while I think we can do better than that Larry Page Introduction to Programming World 1 Chapter 1 Introduction to Programming World In this chapter we will dive into programming world See what programming is what programming languages are talk about some basic topics you should be familiar with before starting programming What is Programming and What are Programming Languages Programming is making the computer do whatever we want it to do And program or software is the name given to a series of computer code to complete a specific task Sometimes the procedure of writing a program is also named as solving a problem because all programs are written to do a specific task in other words to solve a problem you faced in real world Because of the hardware design computers can only understand two states We represent this two state
66. g with GNU Smalltalk Comment to describe this class method we specify the category of this method with lt category Category of this class method gt These were optional things So we don t have to write a comment or specify a category for our method The body of our method does the crucial thing We first declare our local variables localVariablel localVariable2 It is the same as declaring some instance variables Local variables are local to the method and cannot be used out of the method body Then we return the object represented by objectToReturn variable back to the caller with a character in front of it objectToReturn This is called a return expression and will be the famous evaluated value of our message For example when we do 2 3 5 is returned via such an expression Returning a value using a return expression is also optional because of two reasons First the task you are trying to achieve might not need to get any object back Like printing some characters to the standard output Second a method returns the last evaluated expression in the method no matter if we wrote a return expression explicitly or not But it is usually a good programming habit to explicitly return values so that the returned value is more obvious to the reader of the source code The last thing to talk about is the instance method we created anInstanceMethod Comment to describe this instance method category Categ
67. get an error after doing make install like Permission Denied or similar this means you have to log in as super user before applying that command 1 Open your terminal and go to the unix folder under the Tk source code folder where you extracted the Tk source code into In my case cd home canol Desktop tk8 4 19 unix 2 Enter the following commands respectively This will compile the source codes of Tk and make them ready to be used by GNU Smalltalk configure make make install 3 Now we are ready to compile GNU Smalltalk itself Enter the site below ftp ftp gnu org gnu smalltalk and download the latest source code package In my case I downloaded smalltalk 3 1 tar gz 4 Extract the source code package into a convenient folder 5 Go to the GNU Smalltalk source code folder where you extracted the GNU Smalltalk source code into In my case cd home canol Desktop smalltalk 3 1 6 Enter the following commands respectively This will compile the source codes of GNU Smalltalk Installing Programming Environment 85 configure make make install If you didn t get an error while doing these ten steps above then you are now ready to do some coding Installing GNU Smalltalk on Windows Platforms At the time of writing there is unfortunately no Windows installer so to install GNU Smalltalk interpreter to your computer you should compile it from the source GNU Smalltalk can be successfully compiled via MinGW system
68. ginners so we recommend that you finish this text before Now we will mention about the arithmetic part of the two symbol world Though we won t cover it detailed not to bore you with mathematics concepts You can always look at any algebra book to get a deep insight of the materials we will introduce you next Base 10 Decimal Number System We use ten symbols 0 1 2 3 4 5 6 7 8 and 9 to represent the numbers in our daily life Why ten and not nine or eleven Is this how the world is created in ten symbols to represent numbers Of course not We can represent numbers in as many symbols as we want The reason we use ten symbols is that we are used to it It is thought to be used by first Indians and spread the world from there Why Indians choose ten is thought to be because humans have ten fingers Base 2 Binary Number System Mathematics allows us to use as many symbols as we want to represent numbers Because we can use just two symbols in computer architecture base 2 system is ideal for this job Base 2 numbers are Introduction to Programming World 7 usually called binary numbers We choose usually 0 and 1 as the two symbols but have chosen whatever symbol we want We want to show you first how to convert the value of a number written in base x x being a natural number to base 10 When we write a number in base x you can calculate the value of that number in base 10 by multiplying the digit value of each digit b
69. h are called tokens wherever it finds its argument inside the receiver and returns an Array which consists of all the tokens 7 Write a program which holds definitions of some concepts we saw in Chapter 1 in a Dictionary object The program should ask the user to enter a word and then display the corresponding definition 8 What is the difference between Arrays and Dictionarys Why would we use an Array when there is a more featured and charismatic class named Dictionary Objects Messages and Classes Part 43 44 Computer Programming with GNU Smalltalk An intellectual is a man who says a simple thing in a difficult way an artist is a man who says a difficult thing in a simple way Charles Bukowski Controlling the Flow of Execution 45 Chapter 4 Controlling the Flow of Execution The programs we have seen so far executed the codes line by line in the order we write them But real life isn t like this We have to grow up and make some decisions And because programs are to mimic real life problems they as well involve decisions Decisions make the execution of the code lines out of order Some lines of code are executed according to a decision and some lines may never executed at all For example you should get your coat on if the weather is cold or shouldn t if it is hot There is more Controlling the flow of execution of our programs does not just made of decisions There are also repetitions a thing that is not pres
70. hich provides a rich set of classes In this part we will see some of the most commonly used classes and the messages we can send to their instances Although there are hundreds of classes and thousands of messages we cannot cover all of them We will try to give a lot of examples though to make you familiar with GNU Smalltalk code Number Numbers are one of the most commonly used data types in computing Computers are much faster and more accurate than a human being when it comes to manipulate large numbers and doing mathematical operations on them GNU Smalltalk has a Number class which provides a large set of behavior we can benefit from But how are numbers presented in GNU Smalltalk Here are some presentations of numbers We can represent a natural number just like on paper 3 15 1000000 We can add a hyphen character to the beginning of the number to make it negative 3 15 1000000 We can add a dot character as a decimal point 353 9 15 7 Oel We can represent numbers in other bases then decimal We just have to add the base number in decimal we want and an r character to the beginning of the number We use letters starting from A to represent digits greater than 9 while using a base greater then ten 8r312 202 in decimal 16r312 786 in decimal 16rABC 2748 in decimal Scientific notation can be used on GNU Smalltalk too In scientific notation we use an e character to represent exponent of ten So the nu
71. ilarities to form some other groups and also group them to form other groups This process can go on until we reach one main group which is an ancestor of all others This is actually a simulation of life itself The elements we mentioned above are objects and the groups are classes What is the most general expression we use for elements The answer is object We can call everything as an object and then derive a special kind of object from it to which we give names like car house animal etc But remember we call objects which we use to create instances as classes So when we say car house 56 Computer Programming with GNU Smalltalk animal we are actually talking about classes lt Class5 Class6 Class7 Class8 Class9 In this diagram each node represents a class Some classes are derived from other classes Branches are to represent them For example Class2 Class3 and Class4 are all derived from C1ass1 Also Class5 Class6 and Class are derived from Class2 And finally Class8 and Class are derived from C1ass4 We will make two definitions to represent this kind of relationships between classes The classes derived from other classes are called subclasses of the class used for derivation For example Class2 Class3 and Class4 are all subclasses of Classi Also Class5 Class6 and Class7 are all subclasses of Class2 Every class is the superclass of its subclasses For example Classi is
72. ill mention about all this possibilities in this chapter Installing GNU Smalltalk on Linux Platforms There two main ways to install GNU Smalltalk into your Linux system One of them is using the package manager which comes with your Linux distribution and the other one is to compile GNU Smalltalk from its source code Installing via a Package Manager There are several package managers but to name a few of famous ones it is named YUM in Fedora Synaptic Package Manager in Ubuntu and PiSi on Pardus So simply search for Smalltalk with your package manager and install the GNU Smalltalk package with highest version number A version number 3 0 or above would be fine but if it is as old as 2 x then I suggest installing from source code like explained below Installing via Compiling the Source Code Package managers does not always have an up to date GNU Smalltalk package Also it might be the case that your distribution does not come with a package manager at all Then you don t have any choice but to compile GNU Smalltalk by yourself Although it is not as easy as the first case it is not that hard either If you follow the steps we will give below your GNU Smalltalk environment will be ready to use in a few minutes GNU Smalltalk is implemented in C and GNU Smalltalk programming languages So you should have a C compilation environment installed first There is a strong probability that you have them already installed but if it is not the ca
73. ine language Programs written in a compiled language should be translated into machine language by other programs called compiler before the execution by the user Programs written in an interpreted language is converted to machine code during the execution time by other programs called interpreter They do not need a compilation process before they can be executed by the user but they are a little bit slower than compiled machines though this is mostly not a problem anymore for modern computers and for not so performance sensitive projects Although Smalltalk is designed as a language which uses a virtual machine to work GNU Smalltalk acts more like an interpreted language A programming paradigm is how a programming language looks at the problems to be solved Yes Such programming languages are called multi paradigm programming languages No GNU Smalltalk allows programmers to use only object oriented programming paradigm From decimal to binary 543 2 271 remainder 1 271 2 135 remainder 1 135 2 67 remainder 1 67 2 33 remainder 1 33 2 16 remainder 1 16 2 8 remainder 0 8 2 4 remainder 0 4 2 2 remainder0 2 2 1 remainder 0 So the answer is 1000011111 From decimal to octal 90 Computer Programming with GNU Smalltalk We can use the same method to convert it from base 10 to base 8 but we learned an easier way so let s use it 543 001 000011111 1037 I 0 3 T From decimal to he
74. ing Languages eese 1 Programming Language TYPES si ccis ccvssces ets rcp torso eine ae ea er lees voreseats doves EE SEXE e exa eae 1 DAI E acess ay Er E Wega v E K ghd Leaded ENE ARRE O O E M 6 Fule Formats M vise 8 Word Processors Text Editors and IDESs eese nnne eene eene n enne nennen nnn 9 OUI RE 10 Chapter 2 Introduction to GNU Smalltalk 13 Small Talk About Smallialk eren a aee eee ev ve PR e eed E 13 General Logic Behind Smalltalk 4 aee tee iens tete tenete ete a tu apo dnte edge 13 PUP SE PIOSTOAM e 14 Review QUESTIONS MEER 16 Chapter 3 Objects Messages and Classes Part 19 Objects and Messages iode n Oe RS ERES eR R wanes steed esos rU EU RUF Naevi ipt rede ended epu 19 Another Way to Display Output on Terminal eese nennen eene nene rennen 22 Message CHANING E 23 Message Cascading da c de e RR E eim greg ee dedit e peser eode n 23 GU M 24 Common Classes and Their Usage Part I esee enne eene 25 un ME 34 Getting User Tipul orean eee Dye E ree EH ped E HERE aE 35 Common Classes and Their Usage Part Il essere 36 Review QUESTIONS uriene a EEN ENS
75. is is the 2 line Oh my god I m counting backwards This is tbe 1 line This is the end of this chapter In the next chapter we will continue our journey of learning the base concepts of object oriented programming and also learn how to create our own classes Review Questions 1 What is the ultimate goal of the control messages What kind of control messages are there Give a few examples for each type 2 What are blocks Why do we need them 3 What are definite and indefinite loops Specify one message for each type of loops 4 Write the program in Chapter 2 Review Questions which was displaying a diamond like this M again using the concepts we have seen in this chapter Write the program in a way that we can specify how many slashes a side has easily so that we can form smaller or bigger diamonds 5 Write a program which controls if a given number is prime or not and displays the result The 52 Computer Programming with GNU Smalltalk program should continue asking new numbers until number 1 is encountered 6 This one comes from the inspiration of 99 bottles of beer net web site Write a program which outputs the lyrics of the 99 Bottles of Beer song which can be found at http 99 bottles of beer net lyrics html 7 Write a program twice which displays numbers from 1 to 10 by using definite and indefinite loop techniques Which version feels the right one for this task and why 8 Write a program which alw
76. is not the only input device Every device which give us the opportunity to send information to the computer is an input device For example a mouse a scanner a web cam a touch screen may all be specified as input devices Programming languages usually give us to change standard input and output devices so that the computer and the user interacts with each other using different ways and GNU Smalltalk is not an exception Chapter 3 1 An object is a unit which represents a thing in the program It has some definitions how to respond to certain messages it receives from outside usually from us or from other objects which are called methods We communicate with objects via messages we send to invoke the methods inside them Classes are the templates of the objects we want to create We first define a class then produce objects from it 2 Giving a name to an object is called assignment and we call this names variables in programming jargon This is because although a name refers to only one object the object it refers to can be changed any time We need them to hold a data for later use in a program The data might expected to be changing in different parts of a program so giving it a name would be easier for us instead of dealing with its Answers of Review Questions 93 value directly Messages are classified as unary binary and keyword messages We can count reverse and asUppercase as examples of unary messages count and as
77. its instance variables and methods We did quite make some definitions and most probably you didn t understand them completely If so we suggest that you read the above paragraph once more and continue because this concepts are hard to catch if you firstly encounter them After giving a few examples these concepts will be more clear to you Now we will give you some example object amp message expressions How about some arithmetic expressions first Write the code below to GNU Smalltalk interpreter and hit lt Enter gt from your keyboard 3 4 The spaces are not important you can place as many spaces as you want or don t place any space at all You can even put new line characters around character Now we are introduced to a new concept called white spaces White spaces are the name given to space tab and new line characters They are called white space because we simply can t see them Usually white spaces does not have a meaning in programming languages so compilers and interpreters omit them if they are not inside a string expression Now we can return to our arithmetic expression Here our main object in concern is 3 The object we send messages to are called receiver and 3 here is the receiver 4 characters form the message we send to our receiver 3 The message says to 3 Sum yourself with the number I sent and return the result Selectors and Arguments Now we will look into the message we sent above a little more
78. ke below onto the screen Hint Use forward back slash and space characters 2 What can be the advantages and disadvantages of writing a program into a source code file or entering it directly to the terminal in interactive mode 3 What are comments for in GNU Smalltalk source files How can we write them Introduction to GNU Smalltalk 17 4 The power of computers comes from being able to deal with huge amount of data amazingly fast and without doing a mistake Can you write a program which displays numbers from 1 to 1000 onto the screen Would you Imagine how would it be easily possible 5 We called terminal as our standard output Then there should be more output devices Can you think of a few examples 18 Computer Programming with GNU Smalltalk If you don t fail at least 90 percent of the time you re not aiming high enough Alan Kay Objects Messages and Classes Part 19 Chapter 3 Objects Messages and Classes Part Objects and Messages An object is a unit which represents a thing in the program It has its states which are called instance variables and it has some definitions which defines how to respond to certain messages it receives from outside usually from us or from other objects which are called methods We communicate with objects via messages we send them Then the object responses back if he understands our message We have certain syntax rules to write messages and to define objects
79. lk Documentation http smalltalk gnu org documentation This is where you can find further information about GNU Smalltalk There is a user manual as well as library references Useful Sites GNU Smalltalk nttp smalltalk gnu org The official GNU Smalltalk site You can get the latest version of GNU Smalltalk news and 80 Computer Programming with GNU Smalltalk documentation here Also there is a blog section where developers write entries as well as other members of the site Smalltalk org http www smalltalk org A huge source for every kind of information about Smalltalk Stephane Ducasse Free Online Books http stephane ducasse free fr FreeBooks html A site which gives a lot of links to freely available books related with Smalltalk language Planet Smalltalk http planet smalltalk org A blog planet where Smalltalk related blog entries from all over the internet is published One of the best ways to keep you informed about Smalltalk world You can also have your blog posts published on this site by posting to GNU Smalltalk blogs Project Euler http projecteuler net This is a site where there are several hundred programming problems you can find and people try to get a higher rank by solving this problems with any language they want The problems need a little bit mathematics knowledge The site is well organized and solving a problem is a lot of fun You can improve your GNU Smalltalk knowledge and algorithm a
80. m is probably one small step for mankind but one giant leap for you Small Talk About Smalltalk We are going to use Smalltalk programming language to learn about computer programming but actually any programming language although differs in some methodology can be used as a teaching tool as more or less what we do to program the computer is the same in the end Smalltalk has a very special place in computer science history It appeared publicly around the early 80s as a product of Xerox PARC Palo Alto Research Center It was pretty different than the programming languages that far in regards to its vision in object oriented programming and the syntax and environment it used to realize this method of thinking Also it was using a virtual machine concept that was not popular at the time Note Smalltalk has some features which makes it not only a programming language but a whole programming environment But to avoid too much repetition of ourselves we will use the words Smalltalk programming language and Smalltalk programming environment in exchange Smalltalk interestingly was the first programming environment to use a graphical user interface GUI which is like we all use today several windows arranged on monitor which is as a whole called desktop and things like scroll bars buttons and menus placed in windows Smalltalk environment was also being used for networking in Xerox PARC which was not also common at
81. mber we ve written is multiplied by ten s exponent which is specified after the e character 26 Computer Programming with GNU Smalltalk 1e2 is equal to 100 0 3e5 is equal to 30000 0 0015e4 is equal to 15 Fractions can also be represented on GNU Smalltalk by writing two integers around a slash character Fractions are automatically simplified if they can be 3 5 5 3 Now we saw how to represent the numbers we will use let s learn how to do math on those numbers It is a good idea to start with basic mathematical operations We have a binary message named for summation 0 3 0 01 Hyphen is used for subtraction S 3 2 Soc 5 A character not x character is used for multiplication 0 1e 2 1e2 0 d Objects Messages and Classes Part 27 A slash character is used for division GNU Smalltalk will give us a number in fraction or decimal representation whichever it decides is appropriate 50 4 AIMA 0 5 5 ora Double backslash character is used for modulus operation 5 3 2 3 3 between and We can control whether a number is between other numbers or not by using between and selector For example to control if 3 is between 1 and 5 3 between 1 and 5 Teue As you can see GST returned an object named true This is an instance of Boolean class which is used for determining the accuracy of a logical statement Then how is logical inaccuracy represented
82. mbers because octal numbers are shorter and there is an easy converting method from octal to binary number system and vice versa There are also some historical reasons for that so learning it would be sure an honor for us We use digits 0 1 2 3 4 5 6 and 7 to represent octal numbers We can convert a number written in 8 Computer Programming with GNU Smalltalk binary to octal by grouping every 3 digits beginning from right of the number to the left and replacing every group with the octal equivalent of it For example the number 101011001 written in binary system may be represented in octal system like 1010110012531 p M 5 3 1 If the number cannot be evenly divided into groups of three digits we can add 0 to the left of number until it can The reverse operation converting an octal number to a binary number is also straightforward You just convert every digit of an octal number into its binary equivalent and write them next to each other For example the converting process of octal number 531 to binary can be showed like this 5 3 1 101011001 101011 001 Question Can you explain why such conversions are always true Base 16 Hexadecimal Number System Now we will see a number system which is usually harder to imagine at first Base 16 means we will use 16 symbols for writing numbers But we have only 10 of Arabic number symbols So what are we going to do It is acceptable to use a
83. ming loop techniques are better for your case Let s give an example to understand this message better average st Controlling the Flow of Execution 49 A program which evaluates the sum of the numbers entered to demonstrate the whileTrue message sum enteredIntegers lastEnteredInteger sum 0 enteredIntegers 0 lastEnteredInteger 1 whileTrue Transcript cr show Please enter a number To exit the program enter 1 lastEnteredInteger stdin nextLine asInteger sum sum lastEnteredInteger enteredIntegers enteredIntegers 1 Transcript show The average of the numbers entered so far is sum enteredIntegers printString cr Please enter a number To exit the program enter 1 3 The average of the numbers entered so far is 3 Please enter a number To exit the program enter 1 4 he average of the numbers entered so far is 7 2 Please enter a number To exit the program enter 1 3432 The average of the numbers entered so far is 3439 3 Please enter a number To exit the program enter 1 1 The average of the numbers entered so far is 1719 2 This example demands user to enter a number and then calculates and prints the average of them The only way to stop program is to enter the number 1 We hold the entered number in variable called lastEnteredInteger and in every loop we control whether it is 1 or not at the part lastEnteredInteger 1
84. modify the above code directly but there will be times that we don t want to modify the original code For example maybe more than one program is sharing the code and only one of them is 70 Computer Programming with GNU Smalltalk requiring the extended version Then keeping the original code would be a good idea So let s extend our Human class in our new test program Copy and paste the code of older Human class to the indicated area human extended st A program which has an extended version of Human class Put here the code of old Human class Human extend occupation experience getOccupation occupation SetOccupation anOccupation occupation anOccupation getExperience experience setExperience anExperience experience anExperience introduceYourself Transcript show Hello my name is name and I m age printString years old I am occupation cr aHuman experience aHuman getExperience lt aHuman experience aHuman getExperience aHuman experience aHuman getExperience me myFriend Objects Messages and Classes Part l 71 me Human new me setName Canol G kel me setAge 24 me setOccupation an Engineer me setExperience 1 myFriend Human new myFriend setName smail Arslan myFriend setAge 23 myFriend setOccupation an Engineer myFriend setExperience 3 me introdu
85. n t then there are plenty of interesting problems that you can try to solve using GNU Smalltalk Some web sites are given at section Further Reading later in this chapter Another important thing for improving yourself is always being in contact with other Smalltalkers so that you can be informed about latest news on Smalltalk world and also don t feel alone Again some web site mailing list and blog addresses are given at the end of this chapter These were generally advises to improve your practical side because you have been already learning the theoretical things of Smalltalk by reading these book At some point you may get a feeling that you should also improve your theoretical knowledge after all this book is a work in progress and although it covers all the essentials needed to do practical programming it lacks some general advanced programming concepts and some advanced subjects special to the Smalltalk language Also looking at this beautiful language from different point of views would never be harmful That s why we also gave some reading material at the next section Further Reading Smalltalk 80 The Language and its Implementation by Adele Goldberg and David Robson This is the official book which describes the Smalltalk 80 programming language and also mentions about how to implement it This book is also known as the Blue Book You can get a lot of details about Smalltalk programming language by reading this book GNU Smallta
86. name and then write the message we want to sent to it This expression will return or evaluate to objectToReturn We learned how to use instance methods but how about using class methods This expression will give an error ourObjectName aClassMethod Because aClassMethod is not for the instances it is for the class itself We can execute a method for class like this SubclassName aClassMethod Or we can get some help again from the inherited method c1ass for reaching the class of our object and send it the message like this ourObjectName class aClassMethod Here we used chained message concept Note that because the messages are evaluated from left to right our expression turned into SubclassName aClassMethod first Example Now let s write a real example to illustrate all the concepts we learned so far In this example we will create a class for animals A class named Animal will hold information belonging to every animal while two special classes Dog and Cat derived from it will hold information special to that kind of animal 64 Computer Programming with GNU Smalltalk animal st A program which creates some animal classes to illustrate the object oriented concepts Object subclass Animal name animalNumber 0 comment A class for defining animals gt Animal class setAnimalNumber number A class method to set the animal number category accessing animalNumber n
87. nd a message Characters written between single quotes create string objects So here Hello World is a string object We want this object to print itself to the terminal so we should send a message to it The message for this purpose is printN1 The print part is obvious the N1 part indicates that it is going to insert a new line character afterwards If you understand so far you should still be wondering why it displayed the string two times and not just one time It printed the string for the first time because we want it to and it printed that string second time because the overall expression evaluated the value Hello World and in interactive mode the last evaluated expression is printed to the terminal If we would have written a value directly then it would be printed as well because a value always evaluates to itself We can try it by writing a digit as a command Actually a digit is also an object and it will obviously evaluates its own value Let s try it write 3 to the command line You see I hope you saw that you can count on me That s it We ve already written two computer programs But we said that we are going to write the program in two ways So lets do it in an alternative way Now we are going to write the program into a text file and have the GNU Smalltalk interpreter read the instructions from it and then execute it So we won t be in interactive mode this time These text files are called source code Now o
88. ny symbol we want for the rest of it Usually we use the first 6 letters of Latin alphabet A B C D E and F for values 10 11 12 13 14 and 15 respectively In this case while you say that there are 12 chocolates in front of you maybe an alien who comes from a planet using base 16 numbers in their daily life would say that there are C chocolates in front of it and it would be totally acceptable Converting from base 2 to base 16 and vice versa is very alike with conversions between base 2 and base 8 except that this time you deal with 4 digit groups File Formats A file format is how a file is kept in the memory of a computer Files may be categorized mainly in two Binary files and text files We will use files extensively during our programming practice Actually you are using files every time you use computer because every program you use are composed of a file or some files So it might be handy to know a little bit more about the files Binary Files Binary files are files which are used by some special programs written to read that special file format They are represented as zeros and ones in computer memory and their content is created according to some specifications jpeg pdf doc exe are all examples of binary files and need special programs Introduction to Programming World 9 like image viewer or PDF reader to be used Text Files Humans use some files which are just composed of characters so extensively
89. object so first stdin nextLine is executed and then the assignment Common Classes and Their Usage Part II Now we will introduce some other useful classes you will probably use frequently We will also use the variable concept in our examples Array We often need to group some kind of data together and do some tasks on them altogether Usually the data we grouped is connected in some way Maybe a grocery list the movies we like the books we read etc So we need an object that is capable of holding a collection of other objects Array Set and Dictionary classes are all capable of holding several objects together in different ways The first one we will see is the Array class This class holds a limited number of objects in an order new You can create a new Array object by sending new message to the Array class You should supply a number to determine how many objects the array will be able to hold The code below shows an example anArray anArray Array new 10 nil ail oil pil nil pil pil nil nil nil You can enter the lines above respectively or write them into a file and then execute it via sending the script file to the GST interpreter Please enter the lines as we write here because we will take advantage of the GNU Smalltalk memory so that we don t have to create a variable over and over Now our anArray variable refers to an Array object which can hold ten other objects If you entered Objects Messages an
90. od in Number class named cubed so that we can send that message to get the 3rd power of the receiver Programmers often need to do such modifications to a class and GNU Smalltalk provides a way to do it The class might be a built in one or a class written by the programmer So you can add new methods to and modify existing methods in a class General syntax to modify a class is className extend newInstanceVariablel newInstanceVariable2 methodSelector 68 Computer Programming with GNU Smalltalk Every instance variable you create will be added to the class If a method with the same selector has already been defined than the last one will override it and becomes the new implementation If a method with the same selector is not present then it is added If you want to modify the class itself then you should write class after the className like this className class extend newClassVariablel newClassVariable2 methodSelector Notice that this time we create class variables and class methods Now let s create a Human class and then modify it in some ways The core version of Human class will have some common properties and be able to answer to fundamental messages human st The core version of the Human class Object subclass Human name age setName aName name aName getName name setAge anAge age anAge getAge age introduceYourself Trans
91. ogramming looks at the world as an object compound of other objects According to this paradigm everything can be considered as an object For example a computer a television a book etc are all objects Also all of this objects are compound of other objects For example a computer is made by bringing a main board a graphics card a hard disk and some other hardware together which are all again objects Object oriented programming is generally considered as the most close programming paradigm to human thinking So when you write object oriented programs you feel more comfortable and you can focus into solving the problem instead of worrying about the programming language structure rules etc There is no rule that a programming language should be based on only one paradigm and built itself on it Actually there is even a name given languages which allow the coder to use more than one paradigm during programming multi paradigm programming languages Programming languages which allow 6 Computer Programming with GNU Smalltalk programmer to use only one programming paradigm are called single paradigm programming language Smalltalk is one of the first object oriented programming languages and it is a purely object oriented programming language So it is a single paradigm programming language and you will look everything as an object Number Systems We briefly mentioned that computer hardware can only understand ones and zeros N
92. ooks This is because of mainly two reasons First one is my laziness Second one is that Smalltalk is a small and orthogonal language By small we mean there are fewer programming concepts you should learn compared to other languages Smalltalk is built on a few carefully designed rules and concepts By orthogonality we mean there are very few exceptions on Smalltalk compared to other languages Because of this two reasons you will learn almost the whole language in less than 100 pages This doesn t mean the things you can do with Smalltalk is limited In contrast this small set of rules and orthogonality gives you great flexibility so that the only limit is your imagination Also one of the greatest strength of Smalltalk is its powerful and rich library which gives you most of the tools you need out of the box GNU Smalltalk adds even more tools to this valuable toolbox But because we will concentrate in the core language in this first edition of the book we are going to show you only the tip of the iceberg namely only the most important and most frequently used functionality of the library If you are an experienced programmer who wants to learn Smalltalk then you will be surprised by the elegance of this carefully implemented language Andrew S Tanenbaum says Fight Features the only way to make software secure reliable and fast is to make it small Smalltalk is certainly designed by scientists with this mentality in mind Who is
93. operation on paper by yourself As the last thing to do the interpreter prints that object onto terminal Our second example will be the expression below 3 5 bitAt 3 put 1 printNl T2 12 The only difference here is that we parenthesized all the messages before printN1 But the result is a very different one as you can see because the expression in parenthesis is first evaluated and then sent the message printNl Another Way to Display Output on Terminal Before continuing to the next section we will show you another way to display a text on our terminal which we will use frequently throughout this book along with printN1 message Objects Messages and Classes Part 23 With printN1 message we told to a string object to write itself onto terminal But think of this process in a reverse way we could send a message this time to the terminal to write a string object s value onto itself Although the name comes from another concept standard output has the name Transcript in GNU Smalltalk And the message selector to have it display a text is show As you can guess from colon character at the end of the selector it needs an argument which is the string object we want to display Here is an example execute the GNU Smalltalk interpreter via gst command type the below code to the interpreter and hit lt Enter gt Transcript show Hello World Hello World You might have noticed some differences than when we used print
94. ory of this instance method localVariablel localVariable2 objectToReturn We won t mention about the details of this code because it is almost identical with class method except that it does not have any class name in its header which makes it an instance method So it will be present in all of the instance objects we create from this class Creating Objects from Classes After creating a class you can create objects from it by using the pseudo code below Objects Messages and Classes Part ll 63 ourObjectName SubclassName new We sent the message new to create an object from SubclassName But wait We didn t defined a method called new Then how is it possible to use a method called new This is related with the concept of inheritance Every class and hence object has some methods defined by default and new is one of them It provides a way for creating objects from classes and you don t need to define it for yourself every time thanks to inheritance ourObjectName is a reference name which points to the newly created object It is also called a variable Now whenever we write ourObjectName somewhere in our program the interpreter will know which object we are talking about For example if you remember we have defined a method named anInstanceMethod to use with our objects We can send this message to our object by writing an expression like this ourObjectName anInstanceMethod We first wrote our variable s
95. ou are working with some other coders in a big project then you will need comments so that you understand each others code easily So how are we going to have the interpreter execute it Now if GNU Smalltalk GST program is still running in other words your terminal is still showing something like this st gt then press lt CTRL gt d in Linux or lt CTRL gt z and then lt Enter gt in Windows to quit the program Now your terminal should be waiting your commands We will start the GST program again but this time we will send it the path to our source code as an argument Please go to the directory where your hello world st file is located and type the command below gst hello world st UfSiebther Wor Lot After executing the codes written in the source code the GST program will automatically terminate leaving you alone with the forsaken terminal Note that because we are out of the interactive mode the string is printed only once Writing your source code into a file has many advantages You can execute it as many times as you want and keep them for later use so that you don t have to retype all of the program again But using the command line to type a program can be very handy for small tasks or experimental coding which you will frequently do throughout your learning process In the next chapter we will explain the object message and class concepts Review Questions 1 Write a program which displays a diamond li
96. ow L to x 1 2 dot zy Transcript show Transcript show cr 1 to theLength do x 1to x 1 do y Transcript show Transcript show V 1 to theLength x 2 do ty Transcript show Transcript show cr J Please enter the length of the edge of the diamond 5 IN 96 Computer Programming with GNU Smalltalk JE ON it it it X X x Uf WW 3 answer 4 5 st theNumber isPrime i Transcript show Please enter a number theNumber stdin nextLine asInteger i 2 theNumber i 0 whileFalse i i L l s i theNumber ifTrue Transcript show theNumber printString is a prime number cr ifFalse Transcript show theNumber printString is not a prime number It is devidable by i printString cr Je Please enter a number 3 3 is a prime number 6 answer 4 6 st 99 to 1 by 1 do sx Transcript show x printString bottles of beer on the wall x printString bottles of beer cr x gt 1 ifTrue Transcript show Take one down and pass it around x 1 printString bottles of beer on the wall cr ifFalse Transcript show Take one down and pass it around no more bottles of beer on the wall cr bx Answers of Review Questions 97 Transcript cr Transcript show No more bottles of beer on the wall no more bottles of beer cr Transcript sho
97. ow we will explain the reason a little more detailed The hardware used commonly in computers today can track only two states because of their design We can call this states as on and off for example So humans needed a way to describe the world in just two symbols Ways to describe mathematics in two symbols are already implemented so they just needed to represent other things in two symbols For example how can you represent a refrigerator in computer world We can represent it as a collection of some strings Then how can we represent strings with just two symbols Humans developed ways to represent strings in two symbols which we will show you in topic File Formats We presented some states but we should be able to change these states We achieve this via defining some basic commands and constructing more complex ones on top of the more basic ones This is the way from machine language to Assembly language and to higher level languages like the ones we mentioned before in this chapter Question Although we tried to give you an idea of what happens in a computer we won t cover this techniques in detail Maybe you can try yourself to imagine how to create a world in just two symbols This will be really helpful to create an understanding of computer and will be an interesting practice for you After imagining yourself a little bit you may look at the Assembly language to see how Assembly solved this problem Of course it will be very hard for be
98. pen your favorite text editor like Gedit Kate on Linux or Notepad on Windows and write the below code in a new file hello world st A program to print Hello World to the terminal Hello World printNl Now save it as hello_world st This is the source code of our program The characters between double quotes are comments Comments have two purposes one of them is to make the source code clear to reader so that he she understands it faster So they are omitted by the interpreter The second function of them is for documentation purposes We will explain when it is counted as a comment and when a documentation string later For now just know that above strings are comments When we are writing source codes we will write into first line the suggested file name so that you won t waste time thinking about how to name the file How thoughtful we are We will write into the second line a brief explanation of what the program does so that if you wonder what the program does later on these strings will remind you of it Note that these comment strings are optional You can omit them if you want But don t forget that writing comments into source code is a good programming habit because sometimes you will need to maintain your programs months after you write them and even you as the 16 Computer Programming with GNU Smalltalk writer of that program will have difficulty remembering why you have written some of the commands Also if y
99. programming paradigms 4 Can a programming language support more than one programming paradigm Is the secret feature of GNU Smalltalk which differentiates it from other languages supporting more than one paradigm Write the decimal number 543 in binary octal and hexadecimal format Write the binary number 10110100 in decimal octal and hexadecimal format Write the hexadecimal number A93F in binary octal and decimal format ee d x WA What are binary files and text files Can you give some other examples of binary files other than given in this chapter Can you specify a method to determine whether a file format is binary or text 2 http www flos freeware ch notepad2 html 3 http www editpadpro com editpadlite html Introduction to Programming World 11 9 Explain the differences between text editors and word processors Why shouldn t we use word processors to write programs 12 Computer Programming with GNU Smalltalk Unfortunately the current generation of mail programs do not have checkers to see if the sender knows what he is talking about Andrew S Tanenbaum Introduction to GNU Smalltalk 13 Chapter 2 Introduction to GNU Smalltalk We will dive into GNU Smalltalk world and write our first program in this chapter This chapter is rather short compared to others but it has two reasons Firstly you are going to need to read the necessary portion of the Appendix B secondly writing your first progra
100. r 35 subclass 56 overriding 58 superclass 56 Parameter 6 terminal 14 polymorphism 58 text editor 9 precedence 21 Text editor 9 Precedence 2 token 42 program Unary message 21 Programming variable 35 63 programming language virtual machine 5 programming paradigm 5 White space 19 protocol 55 Windows installer 85 receiver 19 word processor 9 repetitive controlling 45 Xerox PARC 13 Postface 107 Postface Now we are at the end of the book our survey of learning the basics of computer programming using GNU Smalltalk We hope you enjoyed this book You can always send feedback to me via the email address you can find below in the section About the Author About the Author Canol G kel is a student at Hacettepe University Department of Electrical and Electronics Engineering Turkey He is also a member of Hacettepe Robotics Society He likes programming computers microcontrollers and also likes learning not using P new programming languages You can reach him via the email address canol canol info or by sending a pigeon post to Hacettepe Universitesi Beytepe Kampusu Ogrenci Evleri J Blok No Z 09 Ankara Turkey
101. ried to give a lot of examples after introducing new concepts Trying to code and run this sample programs by yourself will not only assure that you understand the concept it will give you both confidence and motivation needed to continue There are also little questions waiting for you inside the chapters to guess and probably apply its solution Finally we have prepared review questions so that after reading a chapter you can intensify your knowledge about the new concepts We strongly suggest you trying to solve this questions The answers of the review questions can be found in Appendix B at the end of this book Also most of the programs are available online at http www canol info books computer programming using gnu smalltalk source code zip Font Conventions We used some font conventions throughout the text so that you can differentiate different kind of materials we are talking about easily Beside the Times New Roman font we use for normal content we used an ifalic text to emphasize a first appearance or a definition of a word We used a fixed sized font while mentioning about a code piece We used an italic fixed sized font while mentioning about a code part you are supposed to put a different code according to your tastes the context of the program or your computer s settings etc II The codes which are meaningful even as they are are showed with a sweet purple rectangle at their left side like below a stand alon
102. riting custom classes and overriding a behavior we will sometimes need to refer to the ancestor s definition of the method inside our method This might be the case when we just want to add some additional statements and not want to change the behavior completely Let s see an example In this example we will have a class for creating watches and we will have another class for water resistant watches derived from it watches st A program which defines classes about watches to demonstrate the usage of the super keyword Object subclass Watch style chronometerCapability comment A class for defining ordinary watches setStyle theStyle A method to set the style of the watch style theStyle getStyle A method to get the style of the watch style setChronometerCapability theChronometerCapability A method to specify if the watch has chronometer capabilities chronometerCapability theChronometerCapability Objects Messages and Classes Part ll 75 getChronometerCapability A method to determine if the watch has chronometer capabilities chronometerCapability listYourFeatures A method to print out the features of the watch Transcript show Style self getStyle cr Transcript show Chronometer capabilities self getChronometerCapability printString cr Watch subclass WaterResistantWatch resistanceDepth comment A class for defining water resistant wat
103. s with digits 0 and 1 We will mention about this more detailed later in this chapter Combinations of zeros and ones generate some commands that computer hardware understands We call these command groups which provide a communication between us and computer hardware as programming languages We can write commands with just zeros and ones but this is a very painful method for humans Imagine a stack full of zeros and ones To be able to recognize the commands from it at first sight would took years of experience for a reasonable human being So humans solved this problem by developing an intermediate step between writing programs and executing it They write it in a more understandable most probably in an English like grammar and then convert it into hardware understandable zeros and ones which is called machine language or machine code This converting process is done also with programs called compilers or interpreters Programming Language Types Programming languages are classified according to their various properties We will just mention a few of them High Level and Low Level Programming Languages As we mentioned earlier machine codes are hard for humans to understand So humans developed languages which are like languages that we today speak A language can be categorized according to how close it is to a human language As closer a language is to a machine language as lower level it is In other words as closer a language is to
104. se then you may get your system administrator to install them for you or get help from web page of your Linux distribution to learn how to get them installed GNU Smalltalk uses some GNU tools to provide an easier compilation experience Here are the 10 golden steps for being successful in your life 1 GNU Smalltalk has some extra packages which extends the capabilities of it One of them is named Blox which provides us a way to create graphical user interfaces with GNU Smalltalk Also there is a very useful feature called Class Browser for GNU Smalltalk which requires Blox But Blox package is dependent to two other software called Tcl and Tk So we will first download the source codes of Tcl Tk and compile them Enter the site below 84 Computer Programming with GNU Smalltalk http www tcl tk software tcltk download html and download one of the Tcl and one of the Tk source code packages with tar gz extension In my case I downloaded tcl8 4 19 src tar gz and tk8 4 19 src tar gz 2 Extract the source code packages into a convenient folder 3 Open your terminal and go to the unix folder under the Tcl source code folder where you extracted the Tcl source code into In my case cd home canol Desktop tcl8 4 19 unix 4 Enter the following commands respectively This will compile the source codes of Tcl and make them ready to be used by GNU Smalltalk This steps may take a few minutes configure make make install If you
105. ss variable name animalNumber 0 66 Computer Programming with GNU Smalltalk For documentation purposes we write a class comment comment A class for defining animals gt Now we start defining our methods which provides the behavior of our class First we create a class method to be able to set the animal number Animal class setAnimalNumber number Then we create a class method to get the animal number Animal class getAnimalNumber This kind of set get pairs appear frequently in programming and they are called getters and setters or accessors After that we create our accessors for setting and getting the name of the animal setName newName getName Now that we finished our first class we will create two other classes which derives from it called Dog and Cat Animal subclass Dog Animal subclass Cat Each class derives from Animal class so they already have setName and getName methods We don t need to and should not write them again But we added method with selector makeNoise to each of them We chose such a way because each of the classes make their own sound The rest of the code is for testing purposes We create two objects and try out their methods by sending them appropriate messages dog Dog new Objects Messages and Classes Part ll 67 Animal setAnimalNumber 1 dog setName Karabash dog getName printNl dog makeNoise
106. ster The reader might be another programmer or the programmer who wrote that program himself Even we might not remember what we intended to do with a specific part of the source code when reading it a few weeks later Also in GNU Smalltalk they are used for documentation purposes which we will see later In GNU Smalltalk whatever we write between double quotes are treated as comments by interpreter except double quotes itself If we want to write double quotes in a comment we should write two 92 Computer Programming with GNU Smalltalk double quotes consecutively or we might use single quotes if appropriate for reader 4 We can do that with our current knowledge by writing every single number manually like l printNl 2 printNl 3 printNl 998 printNl 999 printNl 1000 printNl But of course this is not practical and nobody can force us to do that Later on this book we will learn about loops and see how we can achieve this task easily in just one line of code If we imagine about it we will probably come to a point that We should be able to define a range and make the printN1 command act on that range which is the exact solution we will see 5 Everything the computer generously give us is an output It can be an image a sound a movement etc So actually beside our monitor image which is in the form of a terminal text in this case our speakers or a printer may also be classified as output devices Also keyboard
107. t the gt method in Man class such that it sums the points of money and handsomeness and returns true if the receiver s point is higher Add an exception to this rule which is if the name of one of the Man objects is Canol G kel then it is always the better Man Implement the gt method in Women class in a similar manner Sum the points of honesty and generosity than return a true or false object accordingly There is no need for an exception this time after all all the womens are the same 3 Extend the Number class so that it can respond the cubed message by returning the cube of the receiver 4 Explain the purpose of self and super keywords and their difference from each other 78 Computer Programming with GNU Smalltalk One of my most productive days was throwing away 1000 lines of code Kenneth Thompson What to Do Next 79 Chapter 6 What to Do Next How Can Improve Myself Although Smalltalk is a small language syntactically the things that can be done using it is almost unlimited and hundreds of the built in classes and their methods are there to help you We ve covered almost all of the grammatical part of GNU Smalltalk and some of the most commonly used built in classes of it There are still many classes waiting for you to explore and the most effective way to do it is doing practice In programming world practicing means simply writing programs Maybe you already have a project on your mind but if you do
108. the superclass of Class2 Class3 and Class4 Objects Messages and Classes Part ll 57 Derived classes subclasses inherit all the properties and behavior of their ancestors superclasses Some classes in the above diagram have subclasses and every class has a superclass except C1ass1 Notice that classes may have more than one subclasses but they cannot have multiple superclasses An example figure is given below which shows how to create a car and a plane in point of view of the object concept Vehicle Car Plane In this figure each node represents a class There are 8 classes namely Object Engine Body Wing Tire Vehicle Car and Plane Engine Body Wing and Vehicle are all subclasses of Object Car and Plane are subclasses of Vehicle A class may consist of instances of other classes We see examples of that in the Vehicle Car and Plane classes Vehicle class has instances of Engine and Body classes As Car and Plane classes are subclasses of Vehicle they inherited all the properties and behavior of their superclass Vehicle After inheriting the Engine and Body objects we added Car class four Tire objects and Plane class two Wing objects to distinguish them There are two definitions we should make in order not to confuse you about inheritance There might be two kind of relations between objects First an object might have been derived from another object This is called is a relation For
109. the time So when we look at the history of Smalltalk today we realize that it was ahead of its time and influenced the programming languages released after Some of the concepts introduced in Smalltalk is essential today in computer programming If you came across some of the words you haven t seen before in this section don t worry We will learn all the concept we need to know as we go And using this carefully designed elegant simple and yet powerful programming language as the teaching tool will help us understand programming concepts easily than any other General Logic Behind Smalltalk Being a purely object oriented programming language Smalltalk treats everything as an object The communication between objects are provided by sending messages to them For example you create a 14 Computer Programming with GNU Smalltalk computer object and tell it send it a message to open your office suit and it opens Maybe you can create a human object before who owns a computer object Then you can send her a message to send her computer a message to open her office suit The detail level you create depends on the application needs Sometimes you may need to create a human sometimes you don t We will mention more about objects later For experienced programmers In contrast of other popular programming languages like C or Objective C Smalltalk does not allow you to do procedural programming First Program No
110. umber animalNumber Animal class getAnimalNumber A class method to get the animal number category accessing animalNumber setName newName An instance method to set the animal s name category accessing name newName getName An instance method to get the animal s name category accessing name Animal subclass Dog comment A dog class gt makeNoise An instance method to get the dog s noise category accessing Objects Messages and Classes Part ll 65 Woof printNl Animal subclass Cat lt comment A cat class gt makeNoise An instance method to get the cat s noise category accessing Miaow printNl dog Dog new Animal setAnimalNumber 1 dog setName Karabash dog getName printNl dog makeNoise cat Cat new Animal setAnimalNumber 2 cat setName Minnosh cat getName printNl cat makeNoise Karabash Woof Minnosh Miaow 2 Now we will investigate this program line by line We first create our class by inheriting an object named Object which is a special object ancestor of all classes we will create It comes with some useful methods predefined for us like new Object subclass Animal Next thing we do is to declare an instance variable named name and a class variable named animalNumber We will give a name to our animals and keep the number of the animals we created in the cla
111. w Go to the store and buy some more 99 bottles of beer on the wall cr 7 With definite loop answer 4 7 a st 1 to 10 do x x printNl JE 10 With indefinite loop answer 4 7 b st x lt 10 whileTrue x printNl x X 1 10 First one feels the right one because we didn t have to declare a variable and didn t have to increment it manually Also we didn t spend time thinking about the right conditional we just wrote the range This shows we should write a loop using definite loop techniques whenever the range of the loop is known before we enter into it 8 It is impossible to write this program with definite loops because we don t know when the user is going to finish the program In other words how many times the loop will repeat executing itself depends on the task user want to accomplish which the program cannot know so we as the programmer don t know the range of the loop before entering into it By using indefinite loop 5 Actually it is possible but it is hard and unnecessary 98 Computer Programming with GNU Smalltalk Chapter 5 answer 4 8 st newNumber howManyNumbers sum arithmeticAverage newNumber 0 howManyNumbers O0 sum 0 arithmeticAverage 0 newNumber finish whileFalse Transcript show arithmeticAverage printString cr Transcript show newNumber stdin nextLine newNumber isNumeric ifTrue Arithmetic averages
112. w we are going to write our first program in 2 ways But before we start writing you should make sure you got the programming environment installed If you have not installed it yet you should now and Appendix A will help you to do that Our first program will make computer display a text to the terminal or command prompt in Windows terminology Now open up your terminal and type gst GNU Smalltalk ready st GNU Smalltalk interpreter is started and now waiting for commands to execute This is called interactive mode Now we are ready to write our program Type the code below and hit Enter Hello World printNl PEIUS OS Wor Las Hello World Note If you are using an old version of GNU Smalltalk you may need to append an exclamation mark at the end of the code like this Hello World printNl We strongly suggest that you get a newer version of GNU Smalltalk to be able to run all the examples on this book As you can see from the output the computer printed the string He1lo World two times to the terminal which might also be named as standard output in programming terminology Now we will explain this code and why the computer printed the string two times rather than one time As we mentioned everything in Smalltalk is an object and we communicate with them by sending Introduction to GNU Smalltalk 15 messages Then they response us accordingly In the code above we have a string object a
113. which you can find from http www mingw org But you will also need to download the dependencies of the extra packages and compile them before GNU Smalltalk You can get a little bit more information about compiling GNU Smalltalk from Installing GNU Smalltalk on Linux Platform section of this chapter as compiling process in MinGW is alike compiling process on Linux However a process is going on and there is a possibility that a Windows installer will be published soon You can get the installer from GNU Smalltalk official site http smalltalk gnu org download as soon as it is released So keep an eye on the official web site and or send mails to the mailing list if there is a progress on the Windows installer 86 Computer Programming with GNU Smalltalk ASCII Table 87 Appendix B ASCII Table Number Number j Number Number Decimal Binary Character dere if Character Decimal Binary Character Decimal Binary Character 0 000 0000 NUL Null Character 32 010 0000 64 100 0000 e 96 110 0000 1 000 0001 SOH Start of Header 33 010 0001 65 100 0001 A 97 110 0001 a 2 000 0010 STX Start of Text 34 010 0010 0 66 100 0010 B 98 110 0010 b 3 000 0011 ETX End of Text 35 010 0011 67 100 0011 c 99 110 0011 c EOT End of 4 000 0100 Vn CCiOn 36 010 0100 68
114. xadecimal SS ES E 2 F 543 00100001 1111 21F 1 6 From binary to decimal 10110100 0 2 0 2 1 27 0 2 1 2 1 2 0 2 1 27 10110100 0 0 4 0 16 32 04 128 180 From binary to octal 010110100 010 110 100 2 464 ee iG 4 6 4 From binary to hexadecimal 10110100 10110100 B4 B 4 7 From hexadecimal to binary A93F lt 1010 1001 0011 1111 1010100100111111 a a ee eee A 9 3 F From hexadecimal to octal We can look at place value of each digit treat them as octal numbers and sum them up again in octal rules but this is hard for humans because we used to and tend to treat numbers as they are decimal so converting a hexadecimal number to binary and converting it to octal is usually simpler A93F 001 010 100100 111 111 124477 1 2 4 4 7 7 From hexadecimal to decimal Now we can use the method we mentioned above A93F 15 16 3 16 9 16 10 16 A93F 215 484 2304 40960 43327 8 Binary files are composed of zeros or ones placed according to a format specification They can specify any kind of information from a document to image or video Text files are however specially designed binary files to contain only character data using a character set and encoding zip and avi files may be given as examples of other binary files Answers of Review Questions 91 You can try to open a file with a text editor and if it contains only meaningful chara
115. y the base number raised to digit s algebraic order and summing all of them Definition is a little bit confusing isn t it Let s give an example Suppose we have a number written in base 10 like this 345 We can evaluate the same value of this number like this 345 5 10 4 10 3 10 So in base 2 we can write the same number like 101011001 101011001 1 2 40 2 40 3 41 2 4132 024 125 2 410 This is how we convert a base x number into base 10 Now we will show you how we can convert a base 10 number into a base 2 number Suppose that we want to represent number 345 in base 2 All we have to do is to divide 345 to 2 repetitively until we reach a number that can be represented in base 2 Then we write the resulting number and the remainders of previous divisions next to each other from right to left To show this process 345 2 172 remainder 1 172 2 86 remainder 0 86 2243 remainder 0 43 2 21 remainder 1 21 2 10 remainder 1 10 2 5 remainder 0 5 2 2 remainder 1 2 2 1 remainder 0 When we write the result of last division and the remainders of the divisions back to beginning from right to left we boldfaced that numbers in the above equations we get 101011001 which is the same as the 2 base equal we proposed Each digit of a binary number is called a bit and 8 bits next to each other are called a byte in computer jargon Base 8 Octal Number System Sometimes we use numbers written in base 8 to represent binary nu
116. y used language today because when a language is close to hardware the control of you over hardware becomes stronger So for doing very fundamental hardware programming Assembly is probably a good choice Also the lower level the language you use the higher control of you over optimization of the code which results in faster programs Of course using Assembly to code an office suit like Microsoft Office just because of the advantages of Assembly would be a silly choice because it will result hundreds of times longer more complex unreadable and that s why unmaintainable code when it would be coded in a higher level language So you should consider all the pros and cons before choosing a programming language for the current project This also means that you may need to choose different languages for different projects Introduction to Programming World 3 Compiled and Interpreted Languages We mentioned that writing a program is done by using programming languages and there is a step of converting the programs we write from human understandable form to computer understandable form This process is called compilation if the entire program is converted into machine language at once and kept in computer memory in that form If the software written in a programming language requires to be compiled before run then this language is called a compiled language The software doing the compiling process is called compiler But if the program is convert

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