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SML.NET User Guide - University of Cambridge

1. process ints and m x string option process Strings end 4 LANGUAGE EXTENSIONS FOR NET 34 functor Wrapper type T struct _classtype W x T with get x end fun wrap x T W x fun unwrap w W w get end structure IntListWrapper Wrapper type T int list structure IntFunWrapper Wrapper type T int gt int Figure 2 Using functors 4 8 2 Class types and functors samples classfunctor At present the CLR does not support parametric polymorphism We therefore restrict the types of methods in classes to be monomorphic However using SML s functor construct it is still possible to parameterise classes on types and values Figure 2 gives an example When applied to a particular type T the functor provides a new class type W and functions wrap and unwrap that convert values between T and W The class types IntListWrapper W and IntFunWrapper W can then be used to pass around objects that wrap up SML values of type int list and int gt int If one wished to use these wrapper classes to for example store SML values in NET collections one would also have to include a hash function and equality test in the class 4 8 3 Interface declarations samplesl interfaces SML NET users may declare their own interface types The syntax of interface declarations is similar to that of classtype declarations but more restricted An interface type must have no constructor no
2. Attributes can be attached to certain but by no means all declarations in an SML NET program using attribute expressions An SML NET attribute expression is an essentially static description of the data required to construct the corresponding instance of the attribute class when demanded to do so by reflection Syntactically an attribute expression is simply an application of an instance constructor of some attribute class to an n tuple of constant arguments n gt 0 For instance we might annotate another class MLClass as follows _classtype MLAttribute this is a class attribute MLAttribute this is another class attribute MLAttribute this is a constructor attribute MLClass with MLAttribute this is a method attribute method end An attribute expression may be further modified by a sequence of mutable field and property initialisers again supplied with constant values The initialis ers are executed in order just after the instance is constructed by reflection For instance attribute instances of the above CSharpAttribute type may be qualified as follows CSharpAttribute where Field SOME field value end CSharpAttribute where Property SOME property value end CSharpAttribute where Field SOME field value Property SOME property value end NB in named arguments we use the name of the property not the name of the set method Ignoring any type annotations used to re
3. directory source source Extends queries or resets path in which source files are searched for structure strid filename strid filename structure strid filename strid filename structure strid structure strid structure structure Extends queries or resets mapping of structures to files signature sigid filename sigid filename signature sigid filename sigid filename signature sigid signature sigid signature signature Extends queries or resets mapping of signatures to files functor funid filename funid filename functor funid filename funid filename functor funid functor funid functor functor Extends queries or resets mapping of functors to files make Compile the current project linking and assembling only if the sources have changed or the target does not exist 3 COMPILING PROGRAMS 16 remake Recompile the current project linking and assembling even if the sources have not changed export strid classname strid classname export strid classname strid classname export export Extends queries or resets the set of structures to be exported as NET classes reference libname libname reference libname libname reference reference Extends queries or resets the set of external NET libraries d11s referenced by the current project lib directory directory lib directory directory lib
4. fun nodetoxmldata n XmlNode case n of elem gt XmlElement gt let val SOME name elem ttget_Name val first elem ttget_FirstChild O val children gather first in SOME Elem name List mapPartial nodetoxmldata children end data gt XmlCharacterData gt let val SOME s data get_Data in SOME C stringtoscalar s end _ gt NONE The pattern id gt ty matches only when the examined expression has the class type ty in which case the identifier id is bound to the expression casted down to type ty Cast patterns can be used like any other pattern They can appear in val bindings as in 4 LANGUAGE EXTENSIONS FOR NET 23 val x gt System Windows Forms Window y to give an effect similar to downcasting in expressions but raising SML s Bind exception when the match fails They can also be used in exception handlers such as val result f y handle e gt System Security SecurityException gt 0 in order to handle and possibly deconstruct NET exceptions The order in which handlers appear is important In the example below the exception type DivideByZeroException is a subclass of ArithmeticException so if the handlers were switched the second handler would never be reached fun test x do_some_stuff x handle y gt ArithmeticException gt f y _ gt DivideByZeroException gt g x Finally the behaviour of C s e is c can be emulated by case e of _ gt c gt t
5. 0 and moveVert yinc this move 0 yinc end _classtype ColouredPoint x y c Point x y with getColour c System Drawing Color and move xinc yinc this move xinc 2 yinc 2 end end Figure 1 Coloured points in SML NET The special identifier this has the same meaning as in C referring to the object on which a method was invoked It is used in Point to define horizontal and vertical movement using the more general move method The C language provides a syntax base which allows a method overridden by a subclass to invoke the method that it is overriding Instead we provide a syntax exp method name that can be used only within a class definition on objects of that same class and means invoke method method name in the superclass ignoring any over riding of the method in the current class It is used in ColouredPoint to redefine move using the move method defined in Point making coloured points faster movers than plain points By the magic of virtual method dispatch the moveHoriz and moveVert inherited by coloured points also inherit this speed increase As mentioned in Section 4 4 3 NET allows overloading of methods We support this in _classtype declarations in order to extend existing NET classes that include overloaded methods No special syntax is required the method name is simply repeated in separate declarations as in the example below _classtype C with m x int
6. The second parameter is a pseudo or phantom type that identifies the particular kind of storage cell The kind of a storage cell describes its physical representation and thus the precise runtime instructions needed to implement reads and writes The advantage of introducing a parametric notion of storage cell indexed by kind is that it allows SML NET to treat and as generic operations polymorphic as in ML in the contents of a storage cell but also polymorphic in the physical representation of that cell To achieve this we generalise the Standard ML types of these operations to the following kind polymorphic types in SML NET val ty kind reference gt ty val ty kind reference ty gt unit In practice this means that you can use the same familiar notation and to manipulate all kinds of storage cells even though they compile to rather different runtime instructions 4 7 1 Storage kinds The kind parameter of a storage cell of type ty kind reference can take one of the following forms 4 LANGUAGE EXTENSIONS FOR NET 29 heap used for ordinary Standard ML references this kind describes a single field ML allocated object Standard ML s primitive ty ref type con structor is defined as an abbreviation for the SML NET reference type type ty ref ty heap reference Thus Standard ML s ref function that allocates a new ref cell actually has type val ref ty gt ty ref ty gt ty h
7. convention identifies the entry point for an executable as is the case in C 2 5 Demonstration programs The distribution comes with a few more demos Explore the demos subdirectory for details and documentation 3 COMPILING PROGRAMS 9 3 Compiling programs In this section we discuss in detail the compilation environment provided by SML NET Within the environment you can type help or just to get a list of available commands For details on a particular command type help command 3 1 Command syntax In general a command consists of an alphabetic keyword optionally followed by parameters separated by commas The case of keywords is ignored Parameters representing file or directory names must be enclosed in quotes if they include spaces Most commands set or extend the value of some setting such as a path or filename For these the current setting can be queried by typing the command followed by For example log displays the filename currently used for logging compiler messages 3 2 Mapping of module identifiers to files A multiple module SML NET program usually consists of a collection of top level SML structures and signatures each stored in a separate file In contrast to other compilation managers SML NET does not require the programmer to list explicitly the files making up a project Instead given the location of SML defined structures and types to be exported as classes using export and a means of mapping
8. lib Extends queries or resets path in which dlls are searched for target exe target exe target library target library target Sets or queries whether current project is an executable or a library out name out name out name exe out name exe out name dll out name d1l1 out out Sets queries or resets file name for compiler output and optionally project type run args Runs the current project if executable and built with specified command line arguments cmd command cmd command Runs the specified shell command cd directory cd directory cd Sets or queries the current working directory 3 COMPILING PROGRAMS 17 log filename log filename log Sets compilation log file and starts logging or stops logging on option on option option option off option off option option option Where option is one of debug debug exnlocs debug symfromloc sml seqwithtype warn value warn match warn bind verbose Sets re sets or queries the associated compiler flag ilasm option value option value ilasm option value option value ilasm ilasm Extends queries or resets the additioanl options passed to the NET assembler ilasm Useful for signing assemblies adding resources such as icons etc name Executes commands from file name smlnet 3 17 Trouble with the NET IL assembler ilasm exe There is a bug in the 1 0 and 1 1 versions of ilasm exe the IL assemb
9. 2000 or XP and some of the server side parts of NET require the Server or Professional versions of those operating systems NET Framework Available from http msdn microsoft com net The Redist includes the runtime libraries and tools notably an assembler required to run SML NET The SDK includes full documentation sam ples and other tools e g a disassembler and stand alone verifier which you may find useful Visual Studio NET is also useful if you wish to write parts of your applications in Cf or VB In particular you can de sign user interfaces graphically and then link the autogenerated code with SML NET code An editor The SML NET compiler is not an integrated development environ ment so unless you install the optional support for Visual Studio NET Section 5 you will need a text editor Typically you will run the editor concurrently with the SML NET compilation environment SML NJ compiler optional The SML NET compiler was developed us ing Standard ML of New Jersey SML NJ If you wish to build the SML NET compiler from sources then you will need SML NJ version 110 obtainable from http cm bell labs com cm cs what smlnj 2 2 Installation To install SML NET simply unpack the distribution smlnet tar gz to obtain a directory smlnet The compiler can be run directly from the bin subdirectory but for convenience you may want to extend PATH with this directory IMPORTANT To avoid problems please unpack you
10. A 92 Requirements o icons 58 Installation coe a 4 444555 8S eee eee EE EERE HES 5 4 Working In Visual Studio lt s s o s moo lt ooooooo o 5 4 1 Opening an existing Project 5 4 2 Creating a new Project lt lt o lt Bab Debugging or ias a Ea 5 5 Customizing the Package Installer A Language restrictions AL Cid foe dra aaa A 2 Non uniform datatypes o AS Vale TOSTTICUOD asas a A i E AA Overloading cocida aa rn aa Ge od B The Standard ML Basis Library 1 INTRODUCTION 3 C Support for ML Lex ML Yacc and SML NJ Libraries 43 1 Introduction SML NET is a Standard ML compiler 2 3 for the NET Common Language Runtime Its features are Support for all of Standard ML SML NET compiles all of SML 97 2 ex cept for some minor omissions documented in Appendix A Support for the Basis library Almost all of the Standard ML Basis Li brary 1 is implemented Omissions and discrepancies are listed in Ap pendix B Command line compilation SML NET supports traditional compilation from the command line Interactive compilation environment Alternatively you can control the compiler from an interactive environment This lets you set and query options incrementally and to see the signatures of compiled and imported SML modules Support for Visual Studio NET This distribution includes an optional experimental package for Visual Studio NET that allows you to
11. NET s coverage further PITFALL Cf assumes all attribute class names have the suffix Attribute and allows the programmer to omit the suffix from attribute expressions In SML NET we make no such assumption but require the full name of the at tribute class in attribute expressions 4 10 Exporting structures By default all SML NET declarations are private to the generated executable or DLL In order to make declarations available outside even simply to expose an entry point it is necessary to export selected top level structures using the compiler s export command In the current version of the compiler it is only possible to export structures whose signature can be mapped directly back to NET types The following rules are applied for export e Top level SML structures are exported as NET classes possibly in some namespace if specified by the export command e Value bindings with function type are exported as static methods A function type is exportable if Its result type is an exportable type Its argument type is either unit an exportable input type or a tuple of exportable input types An argument type or tuple component may also be the address of an exportable input type akin to C s ref and out parameters e Value bindings with exportable types are exported as static read only fields e Class interface and delegate type declarations are exported as NET nested classes if The type of
12. SML signature structure and functor identifiers onto file names SML NET determines automatically which files it must compile The most straightforward way to operate is to put each structure strid into a file called strid sml each functor funid into a file called funid sm1 and each signature sigid into a file called sigid sig Users of Moscow ML will be familiar with this pattern The compiler then just starts its dependency analysis from the root structures specified using the export command PITFALL SML NET will not infer dependencies that are not there in the source Thus if your project includes file State sml containing structure State struct val state ref NONE string option end file Effect sml containing structure Effect struct val _ State state SOME initialised end and file Main sml containing structure Main struct fun main case State state of NONE gt 1 SOME s gt print s 0 end 3 COMPILING PROGRAMS 10 then exporting Main alone will drag in State but will not drag in the purely side effecting initialisation code in Effect sml Note that Main does not ref erence Effect either directly or indirectly via the referenced entity State To force the evaluation of Effect you must add an explicit reference to the Effect structure for instance by inserting a vacuous local open Effect in end declaration to Main structure Main struct local open Effect in end fun main case Stat
13. Section 4 7 3 4 7 2 Address operators amp It is possible to take the address of any kind of storage cell including another address reference using the SML NET primitives type ty amp ty address reference val amp i ty kind reference gt ty amp ty kind reference gt ty address reference The amp function allows you to pass any kind of SML NET storage cell including an SML ref to a C method expecting a call by reference parameter marked as ref or out in C by taking and then passing the address of that cell For instance given the C swap function public static void swap ref int i ref int j int temp i i j j temp return 4 LANGUAGE EXTENSIONS FOR NET 30 which is imported with SML NET type val swap int amp int amp gt unit Then we can swap the contents of two ML references as follows val ra rb ref 2 ref 3 val _ swap amp ra amp rb val ref 3 ref 2 ra rb Operationally taking the address of a storage cell returns the address of the particular field storing its contents taking the address of an address is simply the identity 4 7 3 Byref types The various kinds of storage in SML NET fall into two categories storage cells whose representations are first class values of the CLR and storage cells whose representations are second class CLR addresses References of kind address and less obviously classty fieldname field where classty i
14. These are displayed whenever SML s value restriction prevents the generalisation of a type in a val binding see Section A 3 for more details warn match Non exhaustive match warnings default on These are displayed when a case or handle does not handle all possible values and so could result in the Match exception being thrown warn bind Non exhaustive bind warnings default on These are displayed when a val binding can result in the Bind exception being thrown verbose Verbose compiler messages default off 3 12 Additional assembler options ilasm It is sometimes necessary or just convenient to be able to pass extra command line options to the assembler The ilasm command takes a comma separated list of additional options with their values if any For instance ilasm CLOCK KEY keyFile snk instructs ilasm exe to report timings and generate a signed assembly using the key pair in file keyFile snk when next invoked by the compiler see the ilasm exe documentation These settings correspond to the concrete shell command ilasm exe CLOCK KEY keyFile snk Note that the extra options are passed to ilasm in addition to any options already implied by other SML NET settings The commands ilasm and ilasm reset and query the current options 3 COMPILING PROGRAMS 14 3 13 Avoiding stack overflow By default under Windows CLR executables receive a fixed and fairly low ceiling on the amount of stack spac
15. as invocations of a principal constructor e The optional superdecs specifies the superclass that class name extends and any interfaces that it implements The superclass clause which must occur first if at all contains an argument or tuple of arguments exp to pass to the superclass ty constructor If absent this defaults to System Object The remaining types in a superdecs clause must be distinct interfaces e dec is a set of SML declarations that are local to a single instance of the class e The optional methoddecs is a simultaneous binding of instance method declarations defined using a syntax similar to that of ordinary functions but with optional qualifiers final and protected preceding the method identifiers An abstract method is declared by omitting is implementation but declaring its type An abstract method may have an optional explicit abstract qualifier Note that methods may have attributes and that abstract methods must have function types The class definition is bound within its own body allowing recursive ref erences via this the methods of a class can have types that mention the class type itself 7 In keeping with tradition and to demonstrate that classes are usable in SML NET without reference to NET libraries Figure 1 presents a variation on the classic coloured point example Notice the absence of any direct support for field declarations Instead the declarations following local are evalu
16. local declarations no superdec declaring a superclass and base constructor and no concrete method implemen tations dec _interfacetype attributes interface namel superdecs with methoddecs end superdec ty superdecs superdec superdec superdecs methoddec attributes mmod method name ty methoddecs methoddec methoddec and methoddecs The methods of an interface type but not its super declarations may make recursive references to that interface type 8Direct mutual recursion between interface declarations is not yet supported in this release but it can be simulated using forward declarations of interfaces 4 LANGUAGE EXTENSIONS FOR NET 35 4 8 4 Delegate declarations samples delegates SML NET users may declare their own delegate types The syntax of delegate declarations uses a concise form of classtype declaration dec _classtype attributes delegate name of ty e The optional and typically absent attributes lists any class attributes see Section 4 9 e The type argument ty of a delegate must be an SML function type A delegate declaration declares the type delegate name the delegate con structor delegate name of higher order type ty gt classname and implicitly declares an Invoke instance method of the function type ty For example the BinaryOp delegate class of Section 4 3 2 may be declared within SML NET as _classty
17. or a shared library d11 with the following commands target library target exe The default is to produce executables in which case the compiler expects to find some exported structure containing a suitable main function By default the name of the output is X exe for executables whose main function is in structure X or X d11 for DLLs whose first exported structure is X This name can be overridden by typing out name The syntax out X exe and out X d11 combines the action of target and out in a single command To run a successfully compiled executable from within the compilation en vironment type run args where args are the arguments passed to the executable You can log the compiler messages to a file by typing log filename To turn logging off just type log 3 9 Shell commands cmd cd From within the compilation environment you can issue shell commands using the syntax cmd command It is also possible to change the working directory from within the environment cd directory The syntax cd queries its current value 3 10 Printing types and signatures type The command type longid provides type and signature information for any entities with the name longid These entities may be value bindings types structures or exceptions and may come from external NET DLLs the SML Basis or the current project type provides a primitive but extremely useful form of online documentation for use durin
18. the element type must be an interop input type in the sense of Section 4 2 5 4 2 4 Null values samplesl option In NET variables with class or array types known collectively as reference types are allowed to take on the value null in addition to object or array instances Operations such as method invocation field access and update and array access and update raise NullReferenceException if their main operand is null SML does not have this notion and values must be bound explicitly when created Thus operations such as assignment indirection and array access and update are inherently safer than the corresponding operations on NET We wished to retain this safety in our extensions to SML and so interpret a value of NET reference type as non null instance Nevertheless when a NET field of reference type is accessed from SML or a value of reference type is returned from an external method invoked by SML it may have the value null and this must be dealt with by the SML code Also it should be possible to pass null values to NET methods and to update NET fields with the null value Fortunately the SML basis library already defines a type that suits this purpose perfectly datatype a option NONE SOME of a The val0f function of type a option gt a can be used to extract the underlying value raising Option when passed NONE We interpret values of NET reference type that cross the border betw
19. ET to compile and link the program The compiler will put the output in a file Sort exe and the assembler source in a file Sort il Finally run executes the program with the arguments specified Just to prove that we really have compiled a self contained NET program from a command prompt type C smlnet gt Sort 10 Before sorting 30 7 84 61 38 15 92 69 46 23 After sorting 7 15 23 30 38 46 61 69 84 92 C smlnet gt If you have installed the NET Framework SDK you can type check the output using the verifier and look at it using the disassembler C smlnet gt peverify Sort exe Microsoft R NET Framework PE Verifier Copyright C Microsoft Corporation 1998 2001 All rights reserved All Classes and Methods in Sort exe Verified C smlnet gt ildasm Sort exe Most of the classes listed by ildasm were generated by SML NET to implement SML code but Sort is special as it was listed explicitly as a parameter to export At its simplest export is followed by a comma separated list of top level SML structures each of which will be exported as a class with the same name The signature of each structure determines what will appear in the class Functions are exported as static methods and other values are exported as static read only fields There are strong restrictions on the types of functions and values that can be exported described in detail in Section 4 For this example there is just one exported function called main which by
20. NET types in C notation and as fully qualified NET type names that have direct equivalents in SML NET Amongst NET types only the usual SML Basis types have equality status and can be passed as arguments to SML s polymorphic equality operator that is all those in Table 1 except for real Real32 real and exn 4 2 2 Named NET types samples namedtypes Any named NET type class value type enumeration interface or delegate can be referred to from within SML NET using the same syntax as in Cf This syntax works because of the interpretation of NET namespaces as nested struc tures discussed above For example type XMLParser string gt System Xml XmlDocument 4 2 3 Array types samples arrays Single dimensional NET arrays behave almost exactly like SML arrays their size is fixed at time of creation indexing starts at zero equality is based on identity not value and an exception is raised on out of bounds access or up date Therefore the SML type constructor array corresponds to NET s type constructor But see Section 4 2 4 for a discussion of null valued arrays The NET exception System IndexOutOfRangeException corresponds to the SML exception Subscript Some but not all array types inherit from the class System Array so you can invoke methods on values of these array type and cast their array values 4 LANGUAGE EXTENSIONS FOR NET 20 to and from class types The restriction is that
21. SML NET User Guide Andrew Kennedy Claudio Russo Nick Benton Microsoft Research Ltd Cambridge U K V1 2 build 1613 of Friday 02 June 2006 Contents 1 Introduction 1 1 About this document L2 Grene asd Ge be a a a eal dg OS Ge Lo e ce ee a a he a a Oe a OD Oa eae Ee amp LA Mailing let 2 4 24444 ee bebe eee Rane dee a Getting started 2 1 Requirements ee a ek RO Oe EE SEE aa a a 22 AI Re Re 2 3 Configuration Optional lt cooccoccccocerar a 04 24 Example Quicksort cnica iaa a 2 5 Demonstration programs s i secs es e a e waa 000 Compiling programs 3 1 Command Syntaks o AAA de 3 2 Mapping of module identifiers to files 3 3 Specifying a path for sources saaara eaa 3 4 User defined mappings a oo Recompilabion o 4 4 4 44544460 008480444 be A 3 6 Exporting classes to NET coco ee ee es 3 7 Importing classes from NET lt lt O CIDO aan ee GS oR A Pods RR 4 oo Shell commands i4 44 5444445 4404 see dae d 3 10 Printing types and signatures OU o oe ke REA AE OR ele ee ee eee A 3 12 Additional assembler options 0 3 13 Avoiding stack overflow o o e 0005 ld CANNE AP io A A A A ee ERE 3 15 Command files and command line operation 3 16 Summary of Commands o ee ee eae ee ca ee hs 3 17 Trouble with the NET IL assembler ilasm exe CONTENTS 4 Language exte
22. T distribution includes software which is Copyright 1989 1999 by Lucent Technologies See the file SMLNJ LICENCE for details The entirely optional SML NET binary distribution with Visual Studio support includes additional software the Visual Studio packages and an IL as sembler which is Copyright 2002 2003 Microsoft Research Ltd See the addi tional licence file MSR EULA for details The alternative binary and source distri butions that exclude Visual Studio support are NOT subject to the MSR EULA 1 3 Credits The SML NET team is Nick Benton Andrew Kennedy and Claudio Russo The compiler also includes code by George Russell We would like to thank all the others who have contributed code support web space demos test cases gripes and bug reports both to SML NET and to its precursor MLj Gavin Bierman Tom Chothia Stephen Gilmore Dave Halls Bruce McAdam Chris Reade John Reppy Peter Sestoft the SML NJ developers Ian Stark Audrey Tan Team PLClub Bent Thomsen Lone Thomsen Christian Urban 1 4 Mailing list A mailing list for SML NET users has been set up To join the list send mail to smlnet users request jiscmail ac uk To view the archives of the list see http www jiscmail ac uk lists smlnet users html 2 GETTING STARTED 6 2 Getting started 2 1 Requirements Microsoft Windows You can use any of Windows 98 ME NT4 0 2000 XP Home or XP Professional to run the compiler We generally recommend Windows
23. amespace MyLib Executables must have an entry point By default the compiler looks for an exported structure with a function called main or Main with one of the following types val main unit gt unit val main unit gt int val main string option array option gt unit val main string option array option gt int These types correspond to those accepted by the C compiler for main 3 7 Importing classes from NET reference lib In order to import classes from NET libraries and code written in other lan guages it is necessary to name the assemblies roughly speaking DLLs that are required This is done using the reference command reference libname libname The lib command lib directory directory allows a path for searching for dlls to be specified SML NET follows the same rules as C in searching for assemblies 1 The working directory 2 The NET system directory 3 The directories set by the 1ib command 3 COMPILING PROGRAMS 12 4 The directories set in the LIB environment variable Many useful system assemblies are referenced by the config smlnet script run from the bin directory when SML NET starts up If you prefer not to reference all of these the minimal set of references actually required to compile structures in the Basis is mscorlib d11 and System d1l 3 8 Output out target run log The compiler can be instructed to produce an executable exe
24. and more usefully let val r ref Pair 1 2 in r tinvert r end which returns the modified value Pair 2 1 are both legal This works as expected for fields too let val r ref Pair 1 2 in r x 3 r end returns the modified value Pair 3 2 This mechanism applies to all of the storage kinds of SML NET see Sec tion 4 7 By accessing fields or invoking methods on expressions of type ty kind reference you can if required mutate static fields of classes mutable instance fields of objects and value types and even arbitrary addresses 4 5 1 Boxing and unboxing NET provides a uniform object model allowing any value of value type to be viewed at type object and thus stored in collection classes etc In detail every value type has a corresponding boxed representation of proper class type System ValueType and by subtyping System Object Boxing a value allocates a new appropriately tagged object on the heap and copies that value into the object In SML NET the boxed form of a value type is obtained by an upcast eg p gt System Object to some suitable CLR reference type The supertype is typically System Object but may be System ValueType Boxing casts work for primitive types too eg 1 gt object Unboxing an object extracts a value from a heap allocated object but re quires a dynamic type check In SML NET this is achieved by a downcast from some object type to a value type For instance for obj Syst
25. ated when a class instance is created but are accessible from the method declarations for the lifetime of the object In this example we have mimicked private mutable fields using ref bindings x and y with initial values provided by arguments to the constructor xinit and yinit The methods which may be mutually recursive as suggested by the and separator can refer both to these arguments and to the bindings introduced by local The ColouredPoint class derives from the Point class passing two of its constructor arguments straight on to its superclass constructor It has no local declarations and a new method that simply returns its colour Because the declarations are local to the class instance it is not possible to gain access to the corresponding declarations for other instances of the class In C private fields for other instances can be accessed directly for example to implement an equals method In SML NET this can be emulated by providing appropriate get and set methods for the fields Direct mutual recursion between class declarations is not yet supported in this release but can be simulated using forward declarations of abstract classes 4 LANGUAGE EXTENSIONS FOR NET 33 structure PointStr struct _classtype Point xinit yinit with local val x ref xinit val y ref yinit in getX O x and getY y and move xinc yinc x x xinc y ytyinc and moveHoriz xinc this move xinc
26. ckage 5 2 Requirements The package requies the NET Framework 1 0 or 1 1 1 1 is recommended for debugging and an edition of Visual Studio NET 2002 2003 or 2005 other wise known as versions 7 0 7 1 and 8 0 that includes C support such as Professional or Academic editions The Express editions of Visual Studio NET 2005 are unfortunately not suitable 5 3 Installation To install SML NET for Visual Studio simply run the executable install exe included in the distribution By default it installs the SML NET support using the highest version of the CLR for the highest version of VS currently installed on your machine Run install help for more options that allow you to override the inferred defaults To uninstall run uninstall bat or just install exe u 5 4 Working In Visual Studio This section is a very brief guide to working with SML NET projects in Visual Studio NET 5 4 1 Opening an existing Project The distribution comes with a sample Visual Studio Solution This is a graphi cal multi language Game Of Life application the user interface is written in Cf project Client producing executable Client exe but the Game Of Life algo rithm is written in SML NET project Server producing library Server d11 Start VS and open the sample solution file Life2002 s1n Life2003 s1n or Life2005 s1n as appropriate for your version of VS from the directory vs demo Life in your distribution You should be able to com p
27. e state of NONE gt 1 SOME s gt print s 0 end 3 3 Specifying a path for sources source By default the compiler looks for source files in the working directory The command source directory directory specifies a comma separated list of directories to search for source files The directory names are normalized with respect to the directory current at the time source is executed and if source is already set then new directories are appended To display the current path type source and to restore the default behaviour using the working directory type source 3 4 User defined mappings structure signature functor Sometimes it may be necessary to put SML entities in files not conforming to the default naming conventions In this case you can define your own mapping from structure functor or signature identifier to filename The commands structure strid filename strid filename signature sigid filename sigid filename functor funid filename funid filename let you do this The filenames are normalized with respect to the directory current when the command is issued and repeated use of the commands extend the existing mapping Multiple entities can be mapped to the same file in which case the file must contain top level module bindings for each of those entities To find out what file a particular module maps to whether through explicit mapping or the source path and de
28. e they can use during execution This can pose a problem for some functional programs that rely heavily on deep non tail recursive call patterns Fortunately the Windows system utility editbin exe can be used to modify an executable so that it demands a higher ceiling for the stack For example editbin stack 100000000 Sort exe sets a huge ceiling of ca 100MB See the editbin documentation for more details 3 14 Cleaning up The SML NET compiler will cache information assembly metadata sml object files and dependency information in sub directory bin of the distribution and subdirectories smlnetdep and smlnetobj of each directory on the source path To delete this information use the clean bat script clean scrubs the ba sis directories everything cached in bin and in the current directory and its subdirectories Thus executing clean from C gt smlnet should return the dis tribution to a pristine state Use this script when you suspect the compiler has got itself confused rare but possible With this release we do not recommend you have more than one SML NET process going at the same time especially if the projects under compilation share source code other than the basis 3 15 Command files and command line operation A sequence of compiler commands can be collected together in a file name sm1lnet and then executed simply by typing name Inside name smlnet the commands must be separated by newlines A sin
29. e types Every value type derives from the base class System ValueType Value types are passed by value or copying semantics not by reference In SML NET you can use the same syntax for accessing fields and invoking methods on a value of value type as for objects of reference types So for a 4 LANGUAGE EXTENSIONS FOR NET 26 pair p p x p x p swap are all legal Method invocation works at primitive types too eg 1 ToString In SML NET invoking on a value type first copies the value takes the ad dress of the copy and then passes this address as the this argument of the method Similary accessing a mutable field of some value first copies that value This ensures that values are effectively immutable in SML NET a basic require ment for the implementation of a functional language Thus p invert has no effect on the value of p nor does let val r p x in r 1 end The expressions do have side effects but they cannot alter p Some value types do have mutable semantics perhaps employing mutable instance fields that are updated by instance methods Our copying semantics implies that these updates cannot be observed since they mutate a tempo rary copy of the value not the original value itself To cater for such types SML NET supports an alternative invocation semantics In addition to invok ing directly on a value SML NET lets you invoke on any kind of SML NET reference to a value type Thus ref p invert
30. eap reference classty fieldname static used for a static field this kind describes a sta tic field by the name of the class and the name of the field classty fieldname field used for an instance field this kind describes the superclass of the object classty in which the field fieldname is defined the sort of the class is enough to identify whether this is a field of heap allocated NET object or a field of a NET value type C struct type address used to describe the address of a storage cell An address can point to the interior of an ML ref to a static field a stack allocated local variable e g from C an instance field of a heap allocated object or an inlined value type Addresses are an abstraction of all of the above storage types Bear in mind that storage cells of different kinds have distinct types and are thus not type compatible e g it is a static type error to create a list containing both an integer heap reference and an integer static field reference because the kinds of the references are not unifiable Address kinds are used to describe the type of Cf call by reference ref and out parameters and typically occur in the argument types of imported meth ods Because an address can refer to a value on the stack whose lifetime is limited to that of its enclosing stack frame values of address type and instance fields of value types are subject to certain data flow restrictions described in detail in
31. edit build and debug SML NET projects from within the development environment see Section 5 for an overview and additional installation instructions Automatic dependency analysis In either mode of compilation the com piler requires only the names of root modules and a place to look for source code It then does dependency analysis to determine which files are required and which need recompilation Produces verifiable CLR IL The output of the compiler is verifiable MSIL Microsoft Intermediate Language for the CLR Smooth interop with other languages on the CLR SML NET extends the Standard ML language to support safe convenient use of the NET Frame work libraries and code written in other languages for the CLR SML NET can both consume and produce NET classes interfaces delegates etc These extensions are discussed in full in Section 4 Whole program optimization SML NET performs optimizations on a whole program or library at once It usually produces small executables with fairly good performance Its limitations are Though this is an early release and the performance variation is very wide Compared with SML NJ for example some real programs go four times faster and some go ten times slower 1 INTRODUCTION 4 No interactive evaluation The interactive environment is for compilation of stand alone applications or libraries only SML expressions can not be evaluated interactively and the use command is not availab
32. een SML and NET as values of an option type For example the method Join in class System String has the C prototype public static string Join string separator string value This maps to an SML function with signature val Join string option string option array option gt string option 4 2 5 Interop types We will use the term interop type for the types described in the previous sections and new NET types defined inside SML NET code Interop types can be used in SML extensions such as casts overloading implicit coercions and with additional restrictions in exported structures A special case of an interop type is an interop input type Input types describe values that might be passed into SML NET from external NET classes and therefore must assume the possibility of null values for reference types To be precise an interop type is one of the following 1A NET value type primitive or struct Examples int System DateTime 4 LANGUAGE EXTENSIONS FOR NET 21 2 A NET class interface or delegate type defined externally or from within SML NET code by _classtype or _interfacetype see Sections 4 8 1 and 4 8 3 Examples string System IEnumerable System EventHandler 3 An array whose element type is an interop input type Examples string option array System DateTime array 4 Possibly null versions of either of the above Examples string option array option System EventHandler option array option A type i
33. em Object the expressions obj gt Pair and obj gt int unbox the underlying value returning a value Note that like any other downcast these involve a dynamic test and can fail raising System InvalidCastException 4 5 2 Null values In SML NET every non primitive value type has an implictly defined null value bound in the structure of that same name eq Pair null is equivalent to 4 LANGUAGE EXTENSIONS FOR NET 27 Pair 0 0 The null value is provided in case the value type has no associated NET constructor it can be used to initialise a reference prior to setting up its state For example let val r ref Pair null in r x x y Ir Ls 2 end returns the value Pair 1 2 but without calling a constructor 4 6 Enumeration Types samples enums In NET an enumeration type is a distinct value type declared with a set of named constants of that type Every enumeration derives from proper class type System Enum Each enumeration type has an underlying signed or unsigned integral type equivalent to one of the SML NET types IntW int or WordN word for N 8 16 32 64 In SML NET a NET enumeration type is imported as a pseudo datatype of the same name The datatype has a single unary constructor named after the type that constructs an enum from a value of the underlying type The named constants of the enumeration are imported as equivalently named constant con structors abbreviating par
34. fault naming convention use the commands structure strid signature sigid functor funid 3 5 Recompilation make remake When a source file is changed and make or remake is invoked SML NET will recompile that file and if necessary any other files that depend on it This propagation will only happen if the result of elaborating the entity has changed 3 COMPILING PROGRAMS 11 in essence its type If a recompiled structure matches an unchanged signature then no modules which depend on it will be recompiled Command make compiles the current project but links and assembles only if the sources have changed or the target does not exist Command remake compiles the current project but re links and re assembles even when the sources have not changed and the target already exists 3 6 Exporting classes to NET export main The export command indicates to the compiler which top level SML structures are to be exposed as public classes in the compiled executable or library The syntax of export is the following export strid classname strid classname By default structures are exported as top level classes with names match ing that of the SML NET structure For example the command export S M generates two public classes S and M These names can be overridden typically to introduce a namespace For example export S MyLib Classi M MyLib Class2 will produce two classes Classi and Class2 in n
35. g program development It is particularly convenient for checking how SML NET views libraries written in other languages 3 COMPILING PROGRAMS 13 3 11 Options on off There are a large number of compiler options available They are turned on and off using on option and off option and can be queried using option Alternative syntax option or just option to enable and option to disable We document the most useful options here debug Emit debugging information default off If enabled some symbol and line number information is generated in the assembler file and the debug option is passed onto the NET assembler debug exnlocs Exception line number information default on If enabled the compiler will insert appropriate code into the output so that when SML exceptions appear at top level the runtime reports the SML structure and line number where the exception was raised debug symFromLoc Emit truncated source expressions as the symbolic names for their values in debug builds default off This can be useful for viewing the values of intermediate expressions when debugging sml seqwithtype Sequential withtype declaration default off The Standard requires that multiple bindings in the withtype clause associated with datatype declarations are interpreted simultaneously It is arguably more useful to interpret them sequentially as does SML NJ warn value Non generalised type variable warnings default on
36. g to CLR libraries and for implementing new CLR classes inside SML Section 5 docu ments the Visual Studio NET support package 2For programs that make no use of the language extensions it is possible to develop and test them using a compiler such as Moscow ML or Standard ML of New Jersey and then to use SML NET to produce final executables 1 INTRODUCTION 5 1 2 Licence SML NET COPYRIGHT NOTICE LICENCE AND DISCLAIMER Copyright 1997 2003 by the University of Cambridge Permission to use copy modify and distribute this software and its doc umentation for any purpose and without fee is hereby granted provided that the above copyright notice appear in all copies and that both the copyright notice and this permission notice and warranty disclaimer appear in supporting documentation and that the name of the University of Cambridge not be used in advertising or publicity pertaining to distribution of the software without specific written prior permission The University of Cambridge disclaims all warranties with regard to this software including all implied warranties of merchantability and fitness In no event shall the University of Cambridge be liable for any special indirect or con sequential damages or any damages whatsoever resulting from loss of use data or profits whether in an action of contract negligence or other tortious action arising out of or in connection with the use or performance of this software The SML NE
37. gle command can be split over several lines provided that the splits occur following commas This is useful for commands that specify lists of items The special command file config smlnet located in the compiler bin direc tory is interpreted when the compiler is run It is a useful place to set options appropriate to all projects It is also possible to execute compiler commands directly from the command line either before entering the compilation environment to set options such as source for example or without entering the environment at all to build an executable for example Simply precede the command names with hypens or slashes and separate the command from its arguments by a colon instead of a space Identifiers at the end of the line are interpreted as inputs to an implicit make if any make occurs at all then the compilation environment is not entered For example C smlnet gt smlnet source demos sort Sort will compile our quicksort example to produce a file Sort exe and 3 COMPILING PROGRAMS 15 C smlnet gt smlnet verbose will enter the compilation environment in verbose mode 3 16 Summary of commands help command help command command command help Displays command list or more detailed help on a particular command type longid type longid Displays type signatures for entities with name longid values types structures and signatures source directory directory source directory
38. hese interact unpleasantly with type inference our intention is to have typing rules and an inference algorithm such that a program is accepted iff there is a unique resolution of all the method invocations with respect to the rules Use of the most specific rule during inference can lead to type variables becoming bound and hence ambiguities far from the point of the rule s application being resolved in unexpected ways 4 5 Value Types samples valuetypes NET provides support for an extensible set of unboxed structured values called value types C s structs Consider the C declaration of lightweight integer pairs public struct Pair public int x mutable public int y mutable constructor public Pair int i int j x i y j functional swap returns a new pair public Pair swap return new Pair y x destructive swap modifies this pair public void invert int t t x x y y t return Value types like ordinary classes can have fields and instance methods However because value types are sealed cannot be subclassed they do not need to be boxed on the heap otherwise used to provide uniform representa tions nor do they need to carry run time type descriptors used to support checked downcasts and virtual method invocation For the most part you can view instances of value types as structured primitive types Indeed primitive type such as int are valu
39. ile the solution out of the box choose Build Solution To run the solution you may need to first manually set the startup project to be the C Client project For some reason VS sometimes assumes that the startup project is the Server library but this is a d11 and cannot be run One way to set the startup project in the Solution Explorer Window right click on the Client and select Set as Startup Project Now choose Debug Start to run the application You should see a small Life application window appear in the application select File Go to start the animation After running the project try editing file Server sml in the Server sources The SML code should appear in colour in the editor window If not something 5 VISUAL STUDIO NET SUPPORT 40 went wrong with your installation Edit the code any syntax errors will be underlined with red squigglies and displayed in the Task List After you have have built the project at least once you will be able to use Intellisense on SML identifiers see type and build errors in the Task List window set breakpoints in the margin of source code etc Note that Intellisense will only work if the source file participated in the most recent build Also Intellisense will only work against libraries referenced in the most recent build The file Server sml contains some comments suggesting things to try in the Visual Studio editor See the Visual Studio Documentation for more details on using the V
40. isual Studio Editor 5 4 2 Creating a new Project Start Visual Studio NET Choose File gt New gt Project In the New Project dialog box supply a name and location for your new project In the Project Types pane open the folder SML NET Projects In the Tem plates pane double click on the SML NET Application icon The other icon selects a library or d11 project This should create the new project Now select View Solution Explorer You should see a new tab with an SML NET project the icon actually says it is a C project but never mind Click on the name sm1 file in the Solution Explorer tab If it appears in the editor with coloured syntax all is well You can now build Build Build Project and run Debug Start the project When run the skeleton application does nothing but exit New source files may be added to the project by choosing Project Add New Item providing a name for the file expanding the Visual C tree selecting the SML NET subtree and then selecting the appropriate SML Template Every new project includes an SML NET script script smlnet as a project item This script is passed to the batch compiler in both debug and release builds and should be used to set any additional compiler options like referencing ad ditional assemblies including additional SML source directories etc For example to reference the assemblies in files filename filenamen add the following line to script
41. le Whole program optimization Top level SML modules are not compiled in dividually to NET object code Instead some compilation takes place on separate modules type checking translation to the compiler s own inter mediate form and some optimizations but most is deferred until after the linking together of top level modules This improves performance of the generated code but significantly increases re compilation times To give a rough idea it takes a couple of minutes to recompile a 25 000 line SML application on a 1 33GHz Athlon with 512MB of RAM Only CLR types at boundaries of compiled code The exposed interfaces of applications or DLLs compiled by SML NET may only refer to CLR types classes interfaces delegates etc They may not expose SML specific types functions datatypes records etc In particular this re striction means that one cannot compile an arbitrary SML module into a DLL for consumption even by other SML NET programs the module must be either linked into the client program at compile time or use only CLR types at its interface 1 1 About this document This guide is aimed at programmers already familiar with SML The textbook by Paulson 3 is an up to date introduction to SML 97 Section 2 describes requirements installation and takes you through the compilation of a simple program Section 3 presents the compilation environ ment Section 4 describes extensions to Standard ML for interfacin
42. le containing a component of byref type e A method may take a single byref as an argument and may also take a tuple containing a component of byref type 4 Aside from these restrictions addresses can be passed to other methods supporting Pascal style call by reference passing of local variables LANGUAGE EXTENSIONS FOR NET 31 A function or method may not return values of byref type When matching a structure to a signature the implementation of any opaque type in that signature may not be a byref type A byref type may not be used as the type of an argument to an SML NET class constructor or as the type of any value bound in the optional local declaration of an SML NET class declaration This restriction will be lifted in a later release of the SML NET compiler Finally to ensure the above properties are preserved by SML s type in stantiation of polymorphic values and parameterised type constructors type arguments whether explicit or inferred cannot be byref types nor may they be kinds describing byref types Exceptions to this rule and amp which are known to be safe may be instantiated at kinds describing byrefs 4 8 Defining new NET types 4 8 1 Class declarations samples classtype The mechanisms described so far give the SML programmer access to NET libraries but they do not support the creation of new class libraries nor do they allow for the specialisation of existing NET clas
43. ler used by SML NET the debug information in an IL method can be associated with at most one source file In SML NET target code due to inlining a target method will often be associated with more than one source file To avoid the assembler bug SML NET prefers to use its own version of the assembler in bin ilasm exe If for some reason this private ilasm exe does not work on your machine you can simply delete it from the bin directory In that case SML NET will use the ilasm from your NET Framework installation In addition as a less satisfactory workaround in debug mode SML NET will produce a dummy source file with extension m1 containing the concatenation of all sources referenced from the executable It is this dummy file not the original code that is referenced by the debugger and should be used for setting breakpoints but this can be rather confusing to the user The executable bin ilasm exe is Copyright 2002 2003 Microsoft Research Ltd and is covered by a separate licence in file MSR EULA If you are not happy with the terms of this licence simple delete the executable bin ilasm exe 4 LANGUAGE EXTENSIONS FOR NET 18 4 Language extensions for NET A significant aspect of the SML NET compiler is its support for seamless inter operation with other NET languages and libraries The approach taken is the following e Where possible map NET features into equivalent SML features For example static methods are mapped
44. ns For example val adder Binary0p op To actually apply a delegate to some arguments you simple use its virtual Invoke method 4 LANGUAGE EXTENSIONS FOR NET 22 val 3 adder Invoke 1 2 Every delegate has an implicitly defined Invoke method C actually employs syntactic sugar that calls this method under the hood Delegates are reference types with base class System MulticastDelegate Thus they come equipped with a suite of meth ods beyond the crucial Invoke method discussed here see the NET documen tation 4 3 3 Casts and cast patterns samples casts A new syntax is introduced to denote C style casts exp gt ty It can be used to cast an object up to a superclass open System Drawing val c SolidBrush System Color get_Red gt Brush Explicit coercions are sometimes required when passing NET objects to SML functions and constructors as coercions are only applied implicitly when invok ing NET methods The same syntax can also be used to cast an object down to a subclass with System InvalidCastException thrown if the actual class of the object is not compatible A safer alternative that combines downcasting with C s is construct is the use of gt inside SML patterns pat gt ty This can be used to provide a construct similar to type case found in some languages For example this code from demos xq Xmlinterop sml switches on the type of an XmlNode
45. nsions for NET 4 1 Namespaces classes and nesting o 42 WY PGR sss eR ew ee Boe Re EH e AQ Bulta types oo ek ee data 8 42 2 Named NET types 00 5 2 4 200 84484 Sods ALS o AN 424 Nul values ociosos ttm ic a es AO Aerop YPES caca a a ees a he oS Ba IES cos a EEE A a ala 43 1 Creating objects 2 2 44 66244 aaa eR ae 4 3 2 Creating and invoking delegate objects 433 Caste md Cast patterns psa ci ee a ee K 4 4 Fields methods and properties AAA Bid oc babda Be ES A a aa Methods ss 44 a surea eee be A oe ee eh te 4 4 3 Overloading and implicit coercions AD Valle Types o a aw a a a ee ae a ee Se ES 4 5 1 Boxing and unboxing 2 0 2 62 eee eae A52 Nal Vanes spa oe hee EE a ee Ra ow 4 6 Enumeration Types s saae a d a 86048444 4054 8464 AT Storage Types o aas eama aada Ge Me HB Bow e x Anl Storage kinds 2 44 4 465444 cee be ye eee a 4 7 2 Address operators amp o aie Byret types cs esaea aeter ag aaa a 4 8 Defining new NET types 4 8 1 Class declarations 2 0045 4 8 2 Class types and functors e es e ssr oaao wata 43 3 Interface declarations lt c socos oci eaaa aau 2246 4 8 4 Delegate declarations a a 49 Custom Attributes o s s sacs a eR OD e RRA 4 10 Exporting structures 200 a a aa a de obs 5 Visual Studio NET Support Bl ACEROS ea dag aa hw ra ER Boe el is a ave es
46. ort This will provide a convenient way to define classes with both instance and static methods thus mirroring the semantics of class import 5 Visual Studio NET Support Depending on your choice of download your distribution may include an exper imental Visual Studio NET package for SML NET This package extends the Visual Studio Development Environment with SML specific editor and project support Installation of this package is optional and at your own risk The SML editor provides code colouring bracket matching syntax checking Intellisense on both NET and SML NET libraries and even interactive type inference An SML NET project is just a C Makefile project that invokes the SML NET batch compiler It can participate in Visual Studio multi project solutions The package includes simple wizards for creating new SML NET projects and project items As usual a project may be built in a Debug or 11 All implemented in a pure SML NET masquerading as a classic COM component 5 VISUAL STUDIO NET SUPPORT 39 Release configuration Debug executables may be run under the Visual Studio source code debugger Although by no means perfect the debug experience has improved substantially over SML NET 1 1 and is worth another visit 5 1 Licence The Visual Studio package is Copyright 2002 2003 Microsoft Research Ltd and is covered by a separate licence in file MSR EULA Please take the time to read the licence before installing the pa
47. pe BinaryOp of int int gt int This simultaneously declares the type constructor BinaryOp the higher order class constructor val BinaryOp int int gt int gt BinaryOp and the implicit Invoke method of type int int gt int Unlike ordinary SML function types delegates can be exported in the sense of Section 4 10 providing a rudimentary way of inter operating at the level of first class functions 4 9 Custom Attributes samples attributes SML NET like C enables programmers to use and declare new forms of cus tom meta data using attribute classes Programmers can annotate SML NET code with instances of attribute classes whether these classes were imported or declared within SML NET itself These attribute values may be retrieved at run time using reflection The standard example is that a framework might define a HelpAttribute attribute class that can be placed on certain program elements such as classes and methods to provide documentation displayed in meta data aware class browsers Here s a simple attribute class defined in Cf public class CSharpAttribute System Attribute public CSharpAttribute public string Property set public string Field null In SML NET a new attribute class is defined by declaring a class that ex tends System Attribute eg 4 LANGUAGE EXTENSIONS FOR NET 36 _classtype MLAttribute s string option System Attribute with ToString s end
48. pes samplesl references Standard ML has a minimalist type system that supports only one kind of mutable storage cell ty ref with the following interface type ty ref val ref ty gt ty ref val ty ref gt ty val ty ref ty gt unit Operationally the expression ref exp evaluates exp of type ty to some value v allocates a new object containing a single field storing v on the heap and returns a handle to that object of type ty ref and read and write the contents of the field References have identity and may be tested for equality using SML s equality predicate a a gt bool SML NET compiles values of type ty ref to an instance of a private class with a single mutable instance field of type ty However the CLR provides a much wider range of mutable structures static fields of classes instance fields of heap allocated multi field objects and instance fields of stack allocated value types The CLR even provides a general address type to support call by reference parameter passing C s ref and out parameters For interoperation with NET libraries SML NET has to support these kinds of storage as well In SML NET all of these types are described as particular instantiations of a more general type constructor ty kind reference Unlike SML s ref type constructor this type constructor takes two type parameters The first simply describes the type of the value stored in the cell
49. pplication should break into the VS source code debugger The call stack will probably contain a mixture of Cf and SML NET stack frames Clicking on stack frames will take you to the relevant source code You can even step through the program including stepping through SML NET source code and inspecting SML NET bindings in their raw compiled form on the stack Although the situation has improved the SML NET compiler does not al ways produce enough debug information control flow data representations identifier names and source locations are frequently altered or obscured by the various optimisations in the compiler Even so the information that does remain can still be useful in tracking down bugs From version 1 2 of the compiler bindings in the Locals window now enter and exit scope appropriately The values of truncated sub expressions not just identifiers may be reported as locals in the Locals window provided you rebuild your sources with compiler option on debug symFromLoc this is off by default In debug builds constructed values now have a symbolic tag field derived from the constructor name SML NET stack frames displayed in the Call Stack will mostly have meaningful not mangled source names As a convenience values of heap allocated SML types such as tuples records and non flat datatypes now support additional diagnostic ToString and ToString int depth virtual methods that can be invoked in the VS Im mediate windo
50. r separator int count Its type is interpreted as val Split char array option int gt string option array option and can be called using an ordinary function application fun split c char array i int val0f System String Split SOME c i Here is an example of instance method invocation Create an object val xmldoc Xml1Document Invoke an instance method on it val _ xmldoc Load filename 4 LANGUAGE EXTENSIONS FOR NET 25 4 4 3 Overloading and implicit coercions samples overloading NET permits the overloading of methods the definition of multiple methods with the same name within a single class The methods are distinguished by their argument types Furthermore C and other languages support implicit coercion of arguments in method invocations The combination of these features can lead to ambiguity which Cf resolves statically by picking the most specific method with respect to an ordering on argument types rejecting a program if there is no unique such method SML NET allows implicit coercions on method invocation using C s ref erence widening coercions together with an additional coercion from T to T option for any NET reference type T We do not allow C s numeric widening coercions to be implicit as the spirit of SML is to use explicit conversions such as Int64 fromInt for these We do not allow ambiguity to be resolved by C style most specific method rules as t
51. r distribution to a path that does not contain spaces eg C smlnet but not C Program Files smlnet We hope to lift this restriction in a future release On Windows 98 and Windows ME if the compiler is installed somewhere other than C smlnet then you must also set SMLNETPATH to that directory 2 3 Configuration Optional SML NET is designed to support multiple versions of the NET Framework as determined by the values of two environment variables FrameworkDir and FrameworkVersion If these variables are undefined SML NET will infer their values by running the helper program bin getsysdir exe When defined FrameworkDir should specify the machine s installation directory for all ver sions of the NET Framework and FrameworkVersion the particular version of the NET Framework that you wish to target FrameworkVersion must name a subdirectory of FrameworkDir Typical settings might be set FrameworkDir C WINDOWS Microsoft NET Framework set FrameworkVersion v1 1 4322 2 GETTING STARTED 7 WARNING It is strongly recommended that you clean your project when ever you change to a different version of the NET Framework See Section 3 14 NB the Framework environment variables are pre defined when you start a Visual Studio NET 200x Command Prompt so running SML NET from the shell will automatically target the correct NET Framework for that version of Visual Studio 2 4 Example Quicksort To test its operation on a demonstra
52. ries for ML Yacc are in directory smlnet lib parsing and if you wish to incorporate code which has been gener ated by ML Yacc into your project you simply have to place this directory on the SML NET source path and execute the smlnet lib parsing sources smlnet script to map the required module names to the files in this directory see the xq demo for an example of how to do this The ML Lex and ML Yacc tools themselves can be found in the demos directory though if you already have the SML NJ versions there s no particular advantage in running the NET executable versions Separately the smlnet lib smlnj lib smlnet script predefines a mapping from module names to file names that lets you easily use some of the SML NJ utility libraries typically under sm1 src smlnj 1lib Util but the precise lo cation depends on your SML NJ installation This mapping is incomplete in the current release References 1 E R Gansner and J H Reppy editors The Standard ML Basis Library reference manual Cambridge University Press to appear In preparation online reference available at http www standardml org Basis index html REFERENCES 44 Structure Omissions and discrepancies top level no use Array none BinI0O no getPos setPos no functional I O Bool none BoolVector BoolArray Char WideChar CharVector WideCharVector CharArray WideCharArray CommandLine Date General IEEEReal Int Int32 Int8 Int16 FixedInt Largelnt 1n
53. ring option For the most part mutable fields can be treated as if they had SML ref types they can be deferenced using and assigned to using So fields declared by class C public static int counter static public int size instance can be used as if it is an SML reference cell whose contents have type int For example C counter C counter 1 fun size x C x size In fact mutable fields are given special types that are a generalization of Standard ML s ref type constructor see Section 4 7 Every mutable field also gives rise to a type binding of the same name You should think of this as a new kind of SML reference type in reality it just abbreviates a particular storage type describing this kind of field see Section 4 7 val counterRef C counter C counter valc C val sizeRef C size c size 4 4 2 Methods samples methods NET method types are interpreted as follows First void methods are con sidered as having unit result type similarly methods that take zero arguments have unit argument type Second NET supports multiple arguments directly but SML does not so methods with multiple arguments are given a single tuple argument type Finally when arguments and results are objects or arrays their types are interpreted using the option type constructor as described earlier Consider the following method from class System String public static string Split cha
54. rue gt false 4 4 Fields methods and properties Static per class fields and methods are mapped to value and function bindings in SML located in the structure corresponding to their class For example the PI static field in the System Math class accessed from C using System Math PI maps to a value binding for PI in the SML structure System Math accessed using the same syntax Likewise the Cos static method in the same class is mapped to a value binding of Cos in the structure System Math Non static instance fields and methods are handled specially through new syntax for field access and method invocation exp name Here exp is an SML expression with a NET object type and name is the name of an instance field or method Properties are really just Cf syntactic sugar formalizing the commonplace set set design pattern No special support is provided in SML NET so they must be accessed through their underlying methods which have the names get_P and set_P for a property called P We now describe how field and method types are mapped into SML 4 4 1 Fields samples fields Immutable NET fields readonly and const in C are given types as explained in Section 4 2 using option to denote the possibility of null values for objects or arrays For example a field declared in Cf using public static string language_name C 4 LANGUAGE EXTENSIONS FOR NET 24 is interpreted as having type st
55. s a value type not a proper class type belong to this second category In SML NET these are collectively called byref types In the CLR an address can amongst other things be the address of a value allocated on the call stack e g an imported address of C local variable or the address of a field of a value on the stack e g an imported address of a field of a C local variable Such an address is only valid for the lifetime of the stack frame from which it was taken To prevent such ephemeral addresses from being read or written outside their lifetime when they are unsafe dangling pointers the CLR imposes restrictions on values of address type they cannot be stored in static fields or instance fields of CLR values or objects Because SML NET s byref storage types compile to CLR addresses which must obey the CLR s rules byref values and types can only be used in limited ways In detail SML NET imposes the following restrictions e A value of byref type must not occur as a free variable of any function or class declared within its scope this includes anonymous functions A byref type cannot be used as the argument type of a datatype or ex ception constructor A tuple or record cannot contain a field of byref type unless that tuple is the immediate argument to a method or constructor A structure expression may not export a value of byref type A function may take a value of byref type as an argument but not a tup
56. s an interop input type if it is one of 1 or 4 above 4 3 Objects 4 3 1 Creating objects samples new In Cf instances of a class are created using the syntax new class arg arg where arg are the arguments to one of the constructors defined by the class We avoid the need for any new syntax in SML NET by binding the class name itself to the constructor function If there is more than one constructor then the binding is overloaded see Section 4 4 3 Constructors can be used as first class values and implicit coercions are applied using the same rules as for methods see below For example val fonts map System Drawing Font Times 10 0 Garamond 12 0 4 3 2 Creating and invoking delegate objects samples delegates NET and Cf support a kind of first class function called a delegate A delegate object is an instance of a named delegate type that wraps up a method and in the case of instance methods its context Delegate types are mapped to two SML bindings the type itself just as with class types and a function binding for the delegate constructor which takes an SML function as its only argument For example suppose that the following delegate type was declared in Cf public delegate int BinaryOp int x int y This is reflected as an SML type BinaryOp and a function with signature val BinaryOp int int gt int gt BinaryOp used to construct delegate objects from SML functio
57. s decided to diverge from the standard and to raise no exception If there is sufficient interest a future release may include a special version of the Basis in which Overflow is raised Even so this would probably best be used to track down bugs for instance turning an infinite loop into an uncaught exception and not relied on for production code A 2 Non uniform datatypes The SML NET compiler imposes the restriction that occurrences of parame terised datatypes within their own definition are applied to the same type ar guments as the definition In any case datatypes such as datatype a Weird Empty Weird of a a Weird are of limited use in the absence of polymorphic recursion This restriction will be lifted in a future release of the compiler A 3 Value restriction The definition of SML 97 specifies that the types of variables in bindings of the form val pat exp are generalised to allow polymorphism only when exp is a syntactic value non expansive expression 2 Section 4 7 SML NET makes the further restriction that generalisation can only occur if pat is non refutable that is a match will always succeed and not raise the Bind exception An example of a refutable binding is val x nil nil This restriction is also applied by SML NJ version 110 xand it can be argued that it is an omission from the Definition SML NET also prevents generalisation when pat contains ref patterns This second restric
58. ses with new methods coded in SML For this we introduce a new construct whose syntax is shown below dec _classtype attributes Lemod attributes class name pat superdecs with local dec in methoddecs end superdec ty ty exp superdecs superdec superdec superdecs methoddec attributes mmod method name pat exp attributes mmod method name ty methoddecs methoddec methoddec and methoddecs This introduces a new class type class name defined by the following ele ments e The optional and typically absent attributes and attributesa list any class or constructor attributes see Section 4 9 e The optional class modifier in cmod can be abstract or sealed and has the same meaning as in Cf 5In SML NET the values and amp should not be rebound by the user but this is currently not enforced by the compiler You must explicitly write a possibly empty emod phrase to indicate any constructor attributes this avoids ambiguities in the grammar 4 LANGUAGE EXTENSIONS FOR NET 32 e The expression class name pat acts as a constructor header with pat specifying the formal argument or tuple of arguments to the constructor Any variables bound in pat are available throughout the remainder of the class type construct Unlike C multiple constructors are not supported a future enhancement might allow additional constructors to be expressed
59. smlnet reference filename filename Under VS2003 and higher the project tree will also contain a References node but it is completely ignored by SML NET and should not be used to reference assemblies To include additional SML source in directories dirname dirname add the following line to file script smlnet source dirname dirnamen Each project also includes with a README html file with some hints and handy links to the online SML Basis documentation which you can browse within VS and the online SML NET manual also included in the distribution Note that you can easily customize the project Build Rebuild and Clean actions by editing the project s properties select the NMake property subtree and edit the NMake command line properties 12SML NET projects masquerade as C makefile projects 5 VISUAL STUDIO NET SUPPORT 41 5 4 3 Debugging SML NET is able to produce symbolic debug information for use by the Vi sual Studio Debugger and other CLR debuggers such as the free source code debugger available in the NET SDK For some entertainment open a Life solution select the Debug configura tion Build gt Configuration Manager gt Debug and build the solution again see Section 5 4 1 Now set a breakpoint by clicking the grey margin in some SML file some good locations are marked BREAK in file Server sm1 Run the application by choosing Debug Start After selecting File Go the a
60. solve overloading constant values must be literals or values immediately constructed from literals of the follow ing SML NET types string and string option char bool Word8 word Int16 int int Int64 int Real32 real real any imported enumeration type or System Type The precise grammar of attribute expressions is given below attributes atterpseq attexp exp where namedargs end attexpseq attexp atterp attexpseq namedarg fieldname exp propertyname exp namedargs namedarg namedarg namedargs The supported attribute argument types are the ones required by the CLS NET s Com mon Language Subset l0system Type arguments are not supported in this release 4 LANGUAGE EXTENSIONS FOR NET 37 Imported attribute classes will typically have named as well as positional parameters but attribute classes declared in SML NET can only ever have po sitional parameters corresponding to the arguments of the sole class con structor This is simply a consequence of our design SML NET s _classtype declarations cannot explicitly declare named fields or properties In the current release attribute expressions may only be placed on classes class constructors methods interfaces interface methods delegate classes and delegate constructors C provides rather more places for attributes most no tably assembly and parameter attributes if there is sufficient demand we may extend SML
61. structure bindings for nested classes For example within the namespace System Threading reflected as a struc ture Threading inside a top level structure System the class Mutex is mapped to an SML type identifier Mutex to a value identifier Mutex and to a structure Mutex Namespaces and classes interpreted as structures can be manipulated like any other structure in SML they can be rebound constrained by a signature passed to functors and opened Opening of namespaces as structures through open is analogous to Cs using construct However when used with classes as structures the open mechanism is more powerful permitting unqualified access to static fields and methods Also nested namespaces become visible as structures 3This is not supported in the initial release 4 LANGUAGE EXTENSIONS FOR NET 19 NET type C type SML NET type System Boolean bool bool System Byte byte Word8 word System Char char char System Double double real System Single float Real32 real System Int32 int int System Int64 long Int64 int System Int16 short Int16 int System SByte sbyte Int8 int System String string string System UInt16 ushort Word16 word System UInt32 uint word System UInt64 ulong Word64 word System Exception System Exception exn System Object object object Table 1 Correspondence between types in NET and SML NET 4 2 Types 4 2 1 Built in types samples builtintypes Table 1 lists
62. t64 Int N Vector Int N Array 10 List ListPair Math Option OS 0S FileSys 0S Path 0S Process Real Real64 LargeReal RealVector RealArray String WideString Substring WideSubstring TextI0 Time Timer Vector Word Word32 Word8 Word16 LargeWord Word64 Word N Vector Word N Array none Char maxOrd 65535 none none none none extended with amp type and operation setRoundingMode only accepts TO_NEAREST div quot abs don t raise Overflow as above as above none none none none none none none tmpName creates a file no access with A_EXEC none system doesn t do console I O no fromDecimal toDecimal none none none no getPos setPos no functional I O none only wall clock time is measured none none none none none Table 2 Basis structures implemented in SML NET REFERENCES 45 2 R Milner M Tofte R Harper and D MacQueen The Definition of Stan dard ML Revised MIT Press Cambridge Mass 1997 3 L C Paulson ML for the Working Programmer Cambridge University Press second edition 1996
63. the constructor argument is either unit an exportable input type or a tuple of exportable input types as for functions The methods all have exportable types as for functions e A type is an exportable type if it is an interop type see Section 4 2 5 that does make not use of non exported class interface or delegate types A type is an exportable input type if it is an interop input type see Sec tion 4 2 5 that does not make use of non exported class interface or delegate types 5 VISUAL STUDIO NET SUPPORT 38 e All other bindings are non exportable Here is a contrived example structure S struct _classtype Counter init with local val privateRef ref init in current privateRef and setToCurrent i int amp i privateRef end val x 5 val y I m a string val c Counter 5 fun f x x 1 fun prnl x case x of NONE gt SOME s gt print s n end This will be exported as a NET class S with the following Cf pseudo signature public sealed class S public class Counter public Counter int init public virtual int current public virtual void setToCurrent ref int i public static readonly int x public static readonly string y public static readonly C c public static int f int x public static void prin string x A future release of SML NET will support the export of arbitrarily nested structures merging classes and substructures with equivalent names on exp
64. ticular applications of the proper constructor The derived constructors are bound in a separate structure named after the enu meration type The proper constructor and its derived constant constructors can be used in patterns as well as expressions For example values of the C enumeration type public enum MyEnum A B CH A may be manipulated in SML NET as follows type enum MyEnum fun fromInt i MyEnum i fun toInt MyEnum i i fromString B MyEnum B fromString C MyEnum C fromString s MyEnum val0f Int fromString s fun toString MyEnum A A toString MyEnum B B toString MyEnum C C this case is redundant toString MyEnum i Int toString i fun fromString A MyEnum A l l l Whether in a pattern or expression the constructor MyEnum A is completely equivalent to writing MyEnum 0 instead Enumerations like other primitive types are also value types their values can be cast to and from System Enum System ValueType and System Object and can also have methods invoked on them 4 LANGUAGE EXTENSIONS FOR NET 28 Note that in NET the constants defined for an enumeration type are not necessarily exhaustive of the possible range of values nor are they required to name distinct values This feature distinguishes NET enumeration types from the familiar SML pattern of defining an n valued enumeration by declaring a datatype with n distinct constant constructors 4 7 Storage Ty
65. tion program run SML NET in command line mode as shown below C smlnet gt bin smlnet source demos sort Sort SML NET 1 0 Analysing dependencies done Linking modules done Compiling whole program done Compilation succeeded output in Sort exe C smlnet gt This tells SML NET to compile a top level SML structure called Sort assumed to be found in the directory specified demos sort in a file called Sort sml and to produce an executable with the name Sort exe If this is the first time that any SML NET program has been compiled then you will notice that most of the Basis library is compiled too Alternatively first enter the interactive compilation environment C smlnet gt bin smlnet SML NET 1 0 Then type the commands that follow the prompts below source demos sort export Sort make Analysing dependencies done Linking modules done Compiling whole program done Compilation succeeded output in Sort exe run 20 Before sorting 60 37 14 91 68 45 22 99 76 53 30 7 84 61 23 After sorting 7 14 15 22 23 30 37 38 45 46 53 60 61 68 99 quit C Asmlnet gt The source command tells the compiler where to look for SML source files which by default have the extensions sml for structures and functors and sig for signatures The export command specifies the name of a top level SML structure to be exported as a NET class in the executable Then make 2 GETTING STARTED 8 tells SML N
66. tion will be lifted in a future release A 4 Overloading SML NET resolves default types for overloaded constants and operators at each val or fun binding This is a smaller context than that used by other imple mentations but is permitted by the Definition 2 Appendix E The following typechecks under SML NJ and Moscow ML but not under SML NET because x is assumed to have the default type int at the binding of sqr B THE STANDARD ML BASIS LIBRARY 43 fun g x y let fun sqr x X x in sqr x 2 0 y end For maximum compatibility with other implementations a future version of SML NET will use the largest context permitted B The Standard ML Basis Library A large part of the Standard ML Basis Library is implemented Online docu mentation for the basis library may be found at http www standardml org Basis index html Table 2 lists the structures that exist with omissions and discrepancies de tailed to appear C Support for ML Lex ML Yacc and SML NJ Libraries Many people have asked about using SML NET with some of the extra tools and libraries which come with SML NJ This is usually not hard but does involve a certain amount of work writing smlnet scripts to define entity map pings To avoid everybody having to do this independently we have included SML NETified versions of some of the most popular The distribution comes with SML NET versions of the parser generator tools ML Lex and ML Yacc The support libra
67. to top level function bindings in SML e Where there is no obvious equivalent extend the SML language For ex ample new NET classes can be defined within SML using a new classtype construct The sections which follow describe the extensions in detail Each section is accompanied by small example programs illustrating a single feature These live in directories displayed on the right of the section heading 4 1 Namespaces classes and nesting samples structures If one ignores the class hierarchy and instance fields and methods i e a non object oriented fragment of NET then NET classes can be seen and are used as a minimal module system providing a way of packaging together static fields methods and nested classes that are logically related Namespaces in NET provide a further level of structuring grouping together many classes into a single group We model both using the SML module system Top level namespaces e g System are reflected in SML NET as top level structures with nested namespaces e g System Drawing reflected as sub structures e g structure Drawing inside structure System Classes are reflected in SML NET as three separate bindings e as type identifiers see Section 4 2 2 e as values of function type used to construct instances of the class see Section 4 3 1 and e as structures containing value bindings that reflect static fields and meth ods see Sections 4 4 1 and 4 4 2 and sub
68. w to inspect their values at runtime these methods cannot be called from SML NET source code Building in a Debug configuration is equivalent to setting the debug flag of the command line SML NET compiler WARNING Debug configurations inhibit many SML NET optimisations and produce considerably worse compiled code than Release configurations NOTE Your debug experience is affected by the IL assembler used by your installation of SML NET see Section 3 17 for more details 5 5 Customizing the Package Installer The package installer may fail because it cannot locate a tool it requires so we have included its SML NET source code Should you need to fix the installer the code resides in vs install sml and vs RegTools sml with build script vs install smlnet After editing the installer you can rebuild it as follows cd vs bin smlnet install smlnet Note the installer s executable is placed in the root directory of the distrib ution not in vs The installer must reside in this directory to work correctly A LANGUAGE RESTRICTIONS 42 as it uses its own location to infer the location of the compiler binaries A Language restrictions A l Overflow The Standard ML Basis library requires certain arithmetic operations to raise an Overflow exception when the result is not representable e g Int Int A correct implementation in CLR of these Basis operations would have a perfor mance unacceptable in most applications so it wa

SML.NET User Guide - University of Cambridge

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