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EDT A Syntax-Based Program Editor Reference Manual Ross S

1. string highlighting code sequence of FIXNUMs This type of print box represents a simple string with the sequence of FIXNUMs being the ASCII actually the 30 System Architecture SAIL codes of the characters of the string The second type of print box has the form l seq highlighting code sequence of boxes This type of print box is used to represent a sequence of boxes which are to be displayed one after the other The third type of print box has the form indent highlighting code indentation sequence of boxes An indent box is like a seq box except that the sequence is to be displayed starting on a new line and indented by indentation indentation units An indentation unit is currently defined to be 4 spaces indentation can be any non negative or even conceivably a negative integer The indentation is relative to the start of the immediately enclosing seq or indent box It should be noted that the terms indent and indentation are used rather loosely in this manual What I call an indentation is really just a skip to a new line true indentation will occur only if the indentation code is non zero In actual fact a box in the sequence following seq or an indent can be either a true print box or an atom such as a plist atom whose print box property is a print box The latter scheme has the advantage that the low lev
2. 4 To indicate the result of a simple cursor movement command nothing more than a simple change of highlighting should be required unless this would place the displayed size of the cursor outside the desirable range mentioned above In particular the objects on the screen should not appear to move around unduly 5 Suppose that a vertical list needs to be compressed by eliding some of the elements of that list If the cursor is not an element of this list then ellipsis should occur at the bottom of the list so that the elements at the top of the list are still visible If however the cursor is an element of the list then ellipsis should occur at each end of the list so that the elements adjacent to the cursor remain visible 6 If the space available for the nodes to the left and to the right of the cursor node needs to be restricted then it should be allocated amongst the two sets of nodes in proportion to their sizes The routine rebuild_mainscreen is invoked by mainscreen_update whenever the main screen needs to be redrawn This routine does the following a If the entire tree can fit onto the screen without any nodes being elided then the routine maxprint is invoked to display the root This routine is fairly efficient since it knows that every subnode can also be printed in full In particular maxprint is able to call itself recursively System Architecture 35 b The situation is more complicated if the tree ca
3. Once having performed a replacement using lt ctrl gt r you can repeat the search and subsequent replacement without having to restate either the search or replacement pattern by using the lt ctrl gt lt ctrl gt and lt ctrl gt commands lt ctrl gt repeats the most recent search and replacement searching only inside strictly inside the original cursor lt ctrl gt searches after the cursor lt ctrl gt searches first inside the cursor and then after the cursor if no replacement was possible inside the cursor Note that these commands only perform the first possible replacement not all possible replacements at once The editor will not perform a replacement if it would lead to a syntactically incorrect construct Also the node that results from a replacement will retain any name that was previously held by the node that it replaced Comments The editor s parser will accept Ada comments i e preceded by Although it does not yet allow comments anywhere in your program it does allow comments in most reasonable places Reasonable places arc bcfore a compilation unit or in any place 18 User Guide where a declaration or statement could legally appear In particular nonterminals such as lt statement gt and lt declarative item gt can be replaced by Ada comments using the lt ctrl gt p command Note though that any comment will be displayed on a separate line even if it originally appeare
4. Scroll forwards in the menu Scroll backwards in the menu Remove a menu from the screen Pattern Search and Replacement Commands lt ctrl gt T lt ctrl gt a lt ctrl gt w lt ctrl gt of lt ctrl gt s lt ctrl gt v lt ctrl gt gt lt ctrl gt 2 lt etrlor lt ctrl gt lt ctrl gt lt ctrl gt Display Related Commands lt ctrl gt j lt ctrl gt J lt ctrl gt R Miscellaneous Commands lt ctri gt c lt ctrlow lt ctrl gt t lt ctrl gt v lt ctrl gt g lt ctrl gt z Create a pattern variable from a nonterminal Perform a production but with pattern variables replac ing nonterminals Search inside the cursor Search after the cursor Search inside the cursor then after the cursor Repeat the most recent search inside the cursor Repeat the most recent search after the cursor Repeat the most recent search first inside the cursor then after Perform a replacement Repeat the most recent search and replacement inside the cursor Repeat the most recent search and replacement after the cursor Repeat the most recent search and replacement first inside the cursor then after Try to show more of the cursor Display only the cursor Rebuild the display Insert a copy of a previously named node Create a new nonterminal node Go to a previously named node Revert to the previous context Abort a command Halt the editor 38 Appendix B The Ada Implementation Appendix B T
5. we would like to use the low level display routine replace to update the display after such a command rather than have to redisplay the entire tree In order to do this though we need to be sure that space taken up by the cursor node will not change and that we can be sure of the context in which the new cursor should be printed A node id s always_O_indents property is t if a node with this node id will always occupy no more than one line on the screen The property always nil context will be t if nodes with this node id can always be printed in the default context of nil If the always_0_indents property is t for both the old and the new cursor nodes and if the 28 System Architecture always nil context property is t for the new cursor node then the editor knows that it can safely use replace The nodes not below property is used to speed up searching It is a list of all node ids that cannot possibly appear as a descendant of any node having the original node id Thus if we are searching for a node with node id n then the editor will not need to continue the search inside a node with node id m should n appear as an element of the nodes not below property of m In fact for the Ada language implementation each node id currently has its nodes not below property set to nil this will be changed once more of the Ada language is supported This has the effect only of making searching a little less efficient than it could be The final pr
6. Commands to the Editor The commands to the editor are each in the form of control characters That is you hold down the lt CONTROL gt key and type another key depending upon the command In this respect the editor s command interface is rather primitive It will probably be improved sometime in the future Case is significant for example the lt ctrl gt i command is different from the lt ctrl gt I command Often after typing the appropriate control character you will be prompted for further input such as a file name In such cases you type the required input followed by lt cr gt for fn SALARY RANGE 1 N FA PERSON I 0 for y in SALARY RANGE 2 PERSON I PERSON I SALARY amp YEAR J YEAR J SALARY 3 Internal representation of TOTAL TOTAL SALARY LJ PERSON I 0 end loop for J in SALARY RANGE 2 loop one PERSON I SALARY LJ YEAR YEAR J SALARY L J TOTAL TOTAL SALARY amp end loop ft Figure 1 Internal representation of for in SALAKY RANGE 1 loop PERSON I 0 for J in SALARY RANGE 2 loop PERSON I PERSON I1 SALARY LJ YEAR S YEAR JS SALARY LJ TOTAL IO TAL SALARY LJ end loop end loop 6 User Guide File Input Commands Having started up the editor you ll need something to edit One way to get something to edit is to input it from a previously written file The lt ctr
7. Department Copyright Lcland Stanford Junior University May 20 1983 1 2 User Guide Table of Contents Introduction Running the Editor The Editor s Internal Tree The Cursor Commands to the Editor File Input Commands Moving the Cursor Naming Nodes Reverting to the Previous Cursor Position Inserting Copies of Previously Named Nodes Deletion and Undeletion Adding to a List Creating New Nonterminal Nodes Invoking the Parser Productions on Nonterminal Nodes File Output Commands Coercions and Embeddings Patterns and Search Commands Replacement Commands Comments The Display Aborting a Command Halting the Editor 3 System Architecture An Overview of the System The Editor s Internal Tree Form Properties of node ids Properties of Nonterminals Print Boxes Properties of plist_atoms Properties of Print Option Atoms An Outline of the Editor s High Level Display Algorithm Appendices A Summary of Commands B The Ada Implementation gt o o CO ON DO BP HRW WW WC KF Wo Ww WO NY N N WN WN DN HH e e eRe Re Ree e BG PE he A N CWO wot RA OO Vooo NNA NNa O S amp S 36 38 u Parts of Ada that are Not Supported Extensions to the True Ada Syntax Possible Nonterminal Types C References 38 38 38 4l Introduction 1 1 Introduction Recently there has been considerable interest in syntax based program editors Unlike standard text editors syntax based edi
8. also have been derived from the prefix property is used to quickly compute the maxminsize constraints of such a list node The prefix property of g0066 is string 0 indicating an empty string and no indentation of the first statement in the list The prefix_indents property is thus 0 Similarly the suffix property is a list the car of which is a print box to be used for the suffix of the list Since there is nothing in the list node that will follow the suffix the cdr of the list will always be nil suffix_indents plays a role analogous to that of prefix indents The suffix and suffix_indents properties of the print option atom g0066 are the same as the prefix and prefix indents properties respectively System Architecture 33 The separator and separator indents properties are similar except that they deal with the print box that separates adjacent elements of the list The cdr of the separator property specifies the indentation if any of the element that follows the separator The separator property of g0066 is stringO 0 That is the separator is an empty string but the statement following the separator is to be indented by 0 units i e it is printed starting on the next line but with no relative indentation Thus the separator indents property is 1 Note that the separator does not contain a semicolon since semicolons are considered to be a part of Ada statements and not statement separators The context prop
9. commands In each case you will be asked for the name of the pattern to search for These three commands differ only in where they perform the search lt ctrl gt w searches inside the original cursor including the checking of the cursor itself lt ctrl gt f searches after the cursor lt ctrl gt s performs the most thorough search of the three this command searches first inside the cursor and then after the cursor if an occurrence of the pattern was not found inside the cursor If a search is successful the cursor will move to the first occurrence of the pattern otherwise the cursor will stay where it was originally All searches are performed in preorder which can be defined recursively as check the root search the first i e leftmost son in preorder search the second son in preorder search the last i e rightmost son in preorder It turns out that this order of searching is natural in that it corresponds to the same order that the user would naturally perceive by looking at the corresponding program text displayed on the screen Unfortunately this isn t always true for expressions see below It should be explained precisely what is meant by searching after the cursor in terms of the editor s internal tree representation Consider the ordered sequence o of nodes that would be visited during a preorder traversal of the entire tree starting from the root Let o be the largest
10. ctrl gt t lt ctrl gt n lt ctrl gt v or the creation of a new tree e g with lt ctrl gt i lt ctrl gt I or lt ctrl gt W described later Basic movements such as lt ctrl gt and lt ctrl gt t are not taken into consideration This command is useful if for instance you go to another tree with lt ctrl gt t edit for a while and then want to go back to editing the original tree exactly where you left off This command only works at one level the previous cursor positions are not stacked i Inserting Copies of Previously Named Nodes If the cursor is at a nonterminal node then you can fill it in by inserting a copy of any node of a compatible nonterminal type that you have previously named For example if the cursor is at a lt statement gt nonterminal and if you have previously named another expanded statement node foo then by typing lt ctrl gt c foo lt cr gt a copy of foo will be inserted in place of lt statement gt Note that it will be a copy of foo and not foo itself Thus if you go back and change foo you won t alter the new node The editor never shares the same node at different places in the tree it always produces a copy Often a node will be compatible with a large number of different nonterminals For example the node FOO BAR could be inserted using lt ctrl gt c in place of any of lt expression gt lt parameter gt e g as a parameter in a procedure or function invocation
11. definition of match is assymmetric in that pattern variables are treated differently depending on whether or not they occur in the pattern In fact any pattern variable that occurs in the node being tested for a match as opposed to one that occurs in the pattern does not really behave as a variable at all since it matches only an identical pattern variable This assymmetry is intentional since it was felt that providing fu l unification would be more difficult and of only limited usefulness The lt ctr1 gt command can sometimes be useful for creating patterns when starting from a nonterminal node This command is the same as the lt ctrl gt e command selection of a production except that the nonterminal sons of the skeleton node inserted as a result of the production are each replaced by pattern variables For example if the cursor is at a lt statement gt nonterminal then whereas lt ctrl gt e lt cr gt will produce lt NAME gt lt EXPRESSION gt lt ctr1 gt lt cr gt will produce 71 2 Problems can arise because of the fact that the editor represents expressions consisting User Guide 17 of associative operators such as in binary tree form To illustrate consider the expression FOO BAR 1 Does this match the pattern X 1 Unfortunately we cannot be sure If the expression is represented internally as FOO BAR 1 using prefix notation then it will match the p
12. gt lt expression gt iii A procedure name and the closing id of a procedure can be a string e g In true Ada this is allowed only for the names and closing ids of functions iv A pragma has the form pragma lt name gt This is slightly more liberal but no less restrictive than 1 requires Possible Nonterminal Types Here is a list of all possible nonterminal types Note that the only time that the user needs to actually enter a nonterminal type is when he or she is using the lt ctrl gt W command compilation unit A subprogram package specification or body context part A list of context specifications Appendix B The Ada Implementation 39 context specification declarative part declarative item declarative item list declarative item entry declaration list entry declaration object index list index type definition enumeration literal subtype indication subprogram specification formal part parameter declaration unit name component part component declaration statement list statement elsif else part elsif list elsif item delay statement select option list select option select alternative accept statement entry call generic formal part generic parameter declaration generic type definition case list case item A with or use clause at the start of a compilation unit A list of declarative item w A declaration A list of declara
13. is actually compiled before being run by the editor Accordingly the actual files that are input when the editor is set up have the extension FAS The nerve center of the system is the command interface the code for which can be found in the file COMINT EDT Every control character that forms a command to the editor is made to correspond to a LISP function so that typing the control character causes the execution of that particular function with no arguments COMINT EDT contains the definitions of each of these command functions When executed a command function will cause the implementation of the corresponding con trol character command However the command functions do not implement the con trol character command directly Instead they invoke auxilliary routines that directly implement the commands The code for these auxilliary routines can be found in the files CURMOV EDT CURMAN EDT SEARCH EDT and FILEIO EDT By separating the auxilliary routines from the command interface in this way the work that would be involved in altering the command interface is greatly simplified CURMOV EDT contains code that implements the commands that move the cursor node around CURMAN EDT implements the commands that physically alter the cur sor node in some way SEARCH EDT implements patterns searching and replacement FILEIO EDT implements the I O of previously constructed trees from to a file The file TIDSPL EDT contains code that main
14. lt ctrl gt Rightmost son lt ctrlot Parent lt ctrbon Root lt ctrl gt Left brother lt ctrl gt c Leftmost immediate brother lt ctrl gt gt Right brother lt ctrl gt D Rightmost immediate brother Naming Commands lt ctrlon Name the cursor lt ctrl gt N Rename the cursor lt etrl gt Tell me my name Deletion and Undeletion Commands lt ctrl gt d Soft deletion lt ctrl gt D Hard deletion in a list lt ctrl gt u Undelete lt ctrl gt U Simultaneous delete and undelete Insertion into a List lt ctrl gt Insert to the left of the cursor lt ctrl gt Insert to the right of the cursor Invoking the Parser to Fill in a Nonterminal Node lt ctrl gt p Parse from the keyboard lt ctrl gt P Parse from a text file File Output Commands lt ctrl gt o Output the tree being edited in its internal form lt etrl gt 0 Output the tree being edited in text form plaintext or SCRIBE format Productions Coercions and Embeddings lt etrl gt E Display the production menu if at a nonterminal other wise the embedding menu lt ctrl gt e Select a production if at a nonterminal otherwise an embedding lt cetrl gt Q Display the production menu if at a nonterminal other wise the coercion menu lt ctrl gt q Select a production if at a nonterminal otherwise a coercion Appendix A Summary of Commands 37 General Menu Related Commands lt ctrl gt lt ctrl gt lt ctrl gt oc
15. or as an array index and lt choice gt eg in a branch of a case statement User Guide 9 Deletion and Undeletion lt ctrl gt d will delete the cursor node replacing it by an appropriate nonterminal node This can be thought of as a soft deletion since the original node being edited does not vanish completely but instead a nonterminal node is left in its place Exactly which nonterminal replaces the original cursor will often depend upon the context in which the cursor appears For instance considering the example given above if the node FOO BAR were soft deleted using lt ctrl gt d it could be replaced by lt expression gt lt parameter gt or lt choice gt depending upon the context in which the node appeared If the cursor node is part of a list for example a procedure function parameter array index or a statement or declaration forming part of a statement or declaration list then it can be deleted entirely by typing lt ctrl gt D This can be thought of as a hard deletion since nothing is left in place of the original node After the deletion the cursor will move to the right brother of the original node or to the left brother if the original node had been the final element of the list In the special case where the original cursor had been the only element of the list the cursor will move up to this now empty list The editor will not let you perform a hard deletion if such a deletion would make the e
16. test files above have been filed on TEST1 TRE EDT RSF TESTS TRE EDT RSF The lt ctrl gt i command can be tried out on these files User Guide 7 Note that you can use commands such as lt ctrl gt i and lt ctrl1 gt I even if you are editing another tree at the time Moving the Cursor Remember that when you edit a program using this editor you are not editing a piece of program text but rather you are editing the syntactic structure of the program In particular you are editing the tree structured representation that was mentioned earlier Cursor movements for instance should be thought of as movements inside this syntactic structure rather than as movements in any particular direction on the display If you have previously used only standard text editors to compose and edit programs then this difference of emphasis could prove to be difficult at first I believe however that once this concept is grasped the advantages or potential advantages of this editor and other syntax based editors should become apparent The command lt ctrl gt is used to move the cursor to the leftmost son if any of the original cursor For example if the cursor is at a for statement then lt ctrl gt will move it to the for statement s index variable If the cursor is at an if statement lt ctrl gt will move it to the if statement s conditional expression As a third example if the cursor is at the top of a list of two or more state
17. that will be formed as a result of the production For example the pmenulist property of the nonterminal type type def inition is int integer type enum enum type arr array rec record priv private type lpriv limited private type acc taccess System Architecture 29 The emenulist property specifies all possible embeddings on nodes with this nonter minal type As with the pmenulist property it is a list of dotted pairs with the car of each pair being the mnemonic for an embedding The cdr of the dotted pair is a list that begins with the node id of the node into which the original node will be embedded and is followed by a sequence of O s and l s that correspond to the sons of the new node There will be one and only one 1 in this sequence and this 1 indicates where the original node is to be embedded in the new node The emenulist property of all but a few nonterminal types is nil For an example of the emenulist property consider the nonterminal type name The emenulist property of this nonterminal type is index indexed 1 0 select selected 1 0 attr attribute 1 0 all select all 1 opsym select opsym 1 0 Suppose for instance that the cursor is at some name n Then by applying the embedding command lt ctrl gt e the cursor would be replaced by n lt parameter list gt n lt iden tifier gt n lt
18. to be only one print option atom in any context option of a node id s print format property The maxminsize property contains information about the maximum and minimum possible sizes that the node can be displayed in This property is computed by the maxmin routine after first computing the maxoptions and minoptions properties mentioned above The property takes one of three possible forms depending upon whether or not the node is the cursor or has the cursor as one of its descendants If the node is the cursor node then the maxminsize property has the form cursor the minimum size that the node can be printed in the maximum size that the node can be printed in BY size we mean the number of lines that will be taken up when the node is printed minus 1 More precisely it is the total number of skips to a new line that occur when the node is printed expressions for example will always have a maximum and minimum size of 0 Note that all possible eliding is considered when minimum sizes are calculated If the node is not the cursor node and the cursor is not one of its descendants then the maxminsize property has the form notmixed the minimum size that the node can be printed in the maximum size that the node can be printed in The most complex situation occurs if the node is not the cursor but does have the cursor as one of its descendants In such a case we need to know the maximum and m
19. top and or the bottom of a menu whenever it is necessary to use these menu scrolling commands in order to see more of the menu than is currently showing The above remarks concerning how to select items from a menu as well as those concerning the lt ctrl gt C and menu scrolling commands also apply to the coercion and embedding menus coercions and embeddings will be described shortly When using the editor you will often have to decide whether to fill in a nonterminal node by using a production or whether to fill it in by using lt ctrl gt p and typing in text directly from the keyboard lt ctrl gt p is usually quicker for all but the most complicated expressions as well as for simple assignment statements and procedure calls but don t forget the at the end of Ada statements Productions are usually quicker for the more complex statements such as if case and block statements as well as for subprograms and packages Note that any command that fills in a nonterminal node will preserve any name that the nonterminal node originally had File Output Commands It is possible to output the tree that you are editing to a file either in text form or in internal tree form so that it can subsequently be restored using lt ctr1 gt i The lt ctr1 gt 0 command outputs the tree to a file in text form You will of course be asked for the name of an output file The tree will be output to this file in full That is the
20. COMPUTERSYSTEMSLABORATORY DEPARTMENTS OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCE STANFORD UNIVERSITY STANFORD CA94305 EDT A Syntax Based Program Editor Reference Manual Ross S Finlayson Technical Report No 83 245 PAV Report No 21 July 1983 This research was supported by the Advanced Research Projects Agency of the Department of Defense under Contracts MDA 903 80 C 0159 and NOO 039 82 C 0250 EDT A Syntax Based Program Editor Reference Manual Ross S Finlayson Technical Report No 83 245 Program Analysis amp Verification Report No 21 July 1983 Computer Systems Laboratory Departments of Electrical Engineering and Computer Science Stanford University Stanford California 94305 Abstract This report describes an experimental syntax based editor that has recently been developed at Stanford Syntax based editors are unlike conventional text editors in that they use knowledge of the syntactic structure of the item typically a program being edited to provide high level editing operations The editor described in this report is currently being used as an editor for programs written in Ada Other programming languages could also be handled by replacing the appropriate language definition files by those for another language Key Words and Phrases Ada syntax based program editor EDT A Syntax Based Program Editor Reference Manual Ross S Finlayson Stanford University Computer Science
21. Document United States Department of Defense July 1980 2 Teitelbaum T Reps T The Cornell Program Synthesizer A Syntax Directed Pro gramming Environment CACM Volume 24 Number 9 pp 563 573 September 1981 3 Wegner P Self Assessment Procedure VII CACM Volume 24 Number 10 pp 647 677 October 1981
22. atamedia version of the editor is the preferred version at present because the low level display routines for DataDisc terminals are considerably slower than the corresponding Datamedia routines On the other hand the DataDisc has the advantage of having the SAIL keyboard which makes the editor easier to use and of being able to display more lines of text than Datamedias After you start up the editor the screen will be cleared and partitioned in two and the editor will display READY The top portion of the screen is the editor s special display window The editor is built on top of LISP but does not completely hide the underlying LISP interpreter The bottom portion of the screen is in fact set aside for the LISP interpreter and behaves just as if you were talking to LISP alone including printing normal LISP error messages if something goes wrong The Editor s Internal Tree Any program or program fragment that the user edits is represented internally as a tree Each editable part of the program is a node of this tree The root of the tree represents the entire program fragment that is currently being edited The structure of this tree is intended to reflect the structure of the program fragment For example a node representing an Ada for statement has three sons The first son represents the index variable of the for statement The second son represents the discrete range over which this index variable will range The t
23. attern However if the expression is represented as FOO BAR 1 then it will not match the pattern although the subnode BAR 1 would of course match For this reason searching should be used with caution if the pattern contains expanded or partially expanded expressions Replacement Commands Having performed a successful search you can then use the lt ctrl gt r eommand to specify another node as being the replacement pattern This command replaces the found occurrence of the search pattern by an instantiation of the replacement pattern As a result any pattern variable occurring in the replacement pattern that was previously bound as a result of the search will be replaced by the node that this pattern variable was bound to Note that you type the replacement command lt ctrl gt r after having first performed the search To illustrate this suppose that you have found the statement FOO FOO BAR using the search pattern X X Y and that the cursor is still there Suppose that you wish to replace the cursor by the pattern X Y F X Y Z and that you have previously named this pattern N say Then after typing lt ctrl gt r N lt cr gt the cursor will be replaced by FOO BAR F FOO BAR 2Z Now suppose that you had found the same statement using the search pattern X Y Z instead Then the same replacement command would replace the cursor by FOO FOO F FOO FOO BAR
24. ce of an lt expression gt nonterminal Unless a node occurs as the root of a tree however it is al ways possible to uniquely determine a node s nonterminal type by looking at the context in which it appears The function nonterminal_types the code for which is in the file CURMAN EDT performs this task The property is atomic node specifies whether or not such nodes are atomic or leaf nodes For example this property is t for the node ids id identifier num number and of course nonterminal and patternvar For most other node ids it is nil The editor makes use of this property to ensure that the cursor is always pointing to a legitimate node and never inside an atomic node The property is list specifies whether or not such nodes are list nodes List nodes can have a variable number of sons and the list insertion commands lt ctrl gt and lt ctr1 gt can be applied if the cursor is a son of a list node If the node type in question is not a list node then the is_list property of the node id is nil Otherwise it is an integer giving the minimum number of sons that list nodes with this node id could have For example the is_list property of statement list is 0 since an Ada statement list can have as few as 0 elements On the other hand the node id enum type which is the node id of a node that lists the elements in an enumeration type definition has an is list property of 1 since an enumeration type definitio
25. d in source text on the same line as a declaration or statement The Display Whenever possible the editor will display the entire tree being edited including the cursor in full However if the tree being edited becomes too large to display in its entirity then some subnodcs must be omitted or elided from the display Details of the algorithm that the editor uses in such cases to determine which nodes shall be printed and which nodes shall be elided are given in section 3 In general though the root of the entire tree will always be displayed unless this is impossible Also should eliding be necessary the editor will try to keep the displayed size of the cursor within preset limits so that on the one hand the cursor is shown in enough detail and on the other hand the context in which the cursor appears can be clearly seen Currently these limits are 1 f 5 of the size of the screen and 1 2 of the size of the screen Two commands are provided that will enable you to temporarily increase the dis played size of the cursor should you ever feel that the cursor is not displayed in sufficient detail The lt ctrl gt j command will attempt to increase the displayed size of the cursor as much as possible while retaining the same node as before usually the root as being the node that is displayed topmost lt ctrl gt J goes even further in that only the cursor will be displayed i e with none of its ancestors being di
26. d son the statement list is then printed on a new line and indented one unit Finally on a new line and indented O units relative to the start of the if statement the string end if is printed The total indents property of g0070 is 2 An Outline of the Editor s High Level Display Algorithm The high level display routines must determine the following i Which node is to be printed outermost on the screen ii How large should the cursor node be displayed iii How large should the collection of nodes if any to the left of the cursor be displayed iv How large should the collection of nodes if any to the right of the cursor be displayed v Which nodes shall be displayed in full and which nodes shall be condensed or elided There can be no definitive answers to these questions of course However the high level display algorithm that the editor uses is based upon the following hypotheses 1 Unless it is absolutely impossible to do so the root of the tree should be the outermost node that is displayed 2 If the entire tree can be displayed in full with no subnodes elided then it should be displayed in full More generally if it is possible to completely display a node within the space available for it then this should be done 3 Whenever there is a possiblity of flexibility in the displayed size of the cursor the editor should try to keep the size of the cursor within a certain range
27. el display routines can use the atom to store temporary properties of its own At present there arc three possible highlighting codes 0 1 and 4 A highlighting code of 0 is the default and indicates no special highlighting at all A highlighting code of 1 is used for the print box that represents the cursor node A highlighting code of 4 indicates that the print box represents some special item such as a reserved word It should be noted that it is the job of the low level terminal dependent display routines to decide how to use these highlighting codes For example neither the DataDisc nor the Datamedia low level display routines will do anything special when displaying print boxes with a highlighting code of 0 or 4 If however a print box has a highlighting code of 1 then the Data Disc routines will display it in reverse video and the Datamedia routines will display it intensified Neither the DataDisc nor the Datamedia routines treat the highlighting code 4 especially because of the limited range of highlighting options available on these terminals However one can imagine some more sophisticated terminal being able to display code 4 print boxes in boldface for instance so that reserved words would be appear on the screen in boldface It should be noted that despite their similar appearances print boxes are not nodes and the atoms string seq and indent are not node ids Properti
28. erty is the context in which each son of the list is to be printed The context property of g0066 is nil i e the default context The ellipsis property specifies how list elements shall be elided should that be neces sary As usual this property is a list the car of which is the print box for the ellipsis The ellipsis indents property does the usual The ellipsis property of g0066 is string 0 46 46 46 46 46 46 ie the string The ellipsis indents property is 0 Finally the when empty property specifies a print box to be used instead of those specified by the prefix and suffix properties should the list be empty Of course if the node id s is_list property is gt 0 then this property can just be nil because in such a case it will be guaranteed that the list will never bc empty when empty indents does the usual The when empty property of g0066 is string 4 110 117 108 108 59 which is the string null Note that the highlighting is special The when empty indents property is 0 For non list nodes print format atoms have only two properties print fist and total indents The print list property is a list consisting of alternating fillers and son specifiers The first and last elements of the list are fillers When the node is displayed on the screen the items in this list are processed in order A filler has the form n b m b is a print box to be displayed m is either nil if the son gi
29. es named ADA would be different m E E E fer gt Vee Ope a ae ee ey ee Oe r The Editor Kernel The Parser Parse Table Building Routines Internal Tree Forms node ids ete with Property Lists Node ADA TAB ADA FAS Parse Routines PARSEX SEARCH EDI High level Display Routines ieee Terminal Dependent aaah Raa and I O part Command Interface 54 mainscrcen update Routines display menu forzet current image gt enlarge cursor 1 wee ertlarze cursor 2 General File 1 0 COMINT EDT Routines plus LexicalScanner i Ea openwrite 10 closewrite simple update draw Low level Display Routines DMDPY or DDDPY highlight i replace Figure 3 The logical components of the system Language Description Files Internal Representation and Printing Information ADA INT Node Building Routines ADA BUI External Grammar ADA SYN Preprocessing Part inonterm internal SLR 1 Parse Table LISP Compiler Generator Preprocessing SLRX NCOMPL Routines LNGUAG EDT Parse Table Building Routines internal Tree forms node ids etc with Property Lists ADA TAB ADA FAS Figure4 The Preprocessing Phase System Architecture 23 It should be noted that the code in most of the files with extension EDT
30. es of plist_atoms The plist atom of any node contains various properties that describe that particular node alone Recall that the plist_atoms of every node are distinct These properties are described below If the node has a name then this name will be given by the my name property of the plist atom System Architecture 31 Apart from the my name property mentioned above all of the properties on a node s plist_atom are used by the high level display routines The print box property gives the print box if any of the node If the node is currently displayed on the screen then this property will exist i e be non nil The converse of this is not necessarily true it is possible for a node not to be visible on the screen but to still have a print box property This can happen if the node was visible at some earlier stage The property currently showing is t if the node is currently displayed on the screen and nil otherwise The properties maxoptions and minoptions are each a list of print option atoms that describe how to display the node so as to use up the greatest and least number of lines on the screen respectively In the current Ada language implementation each of these properties will always consist of a one element list Furthermore the single element of the list i e the print option atom will be the same for both the maxop tions and minoptions property The reason for this is that as mentioned earlier there happens
31. etails of the implementation which when supplemented by the separate Implementation guide will be of use to maintainers of the system In particular it makes reference to many of the source code files on SAIL An Overview of the System The editor as a whole consists of several distinct units However it is possible to conceptually group these units together to form five main logical components Firstly there is the editor kernel This can be thought of as the editor proper It consists of the tree s being edited as well as all of the code responsible for interpreting and implementing the user commands that were described in section 2 It also includes the high level display routines which construct the print boxes to be output to the screen print boxes are described later The code for the editor kernel does not depend upon any particular operating system or terminal The second component is the terminal dependent and I O part This consists of routines responsible for opening and closing files for I O and also includes the lexical scanner that is used by the parser In addition it includes low level display routines which take the print box information produced by the high level display routines in the editor kernel and display it on the user s screen Accordingly these low level routines are of necessity terminal dependent Thirdly there is the parser The parse routines use the parse table and the
32. f any of these cursor movement commands does not change the structure of the internal tree in any way All that is done is that a new node of this tree becomes known as the cursor Commands which actually change the node being edited will be described later 8 User Guide Naming Nodes All commands which create and move the cursor to new trees require you to give a name for the root of that new tree In fact you can give a name to any node the lt ctrl gt n command is used to name the cursor You should note that such names are used only for editing purposes and do not appear on the screen In particular they have no relation to any program labels that may be present Anything that would be a valid LISP atom can be used as a name The editor will not let you use a name that is already in use and you cannot use the lt ctrl gt n command if the cursor already has a name If the cursor already has a name and you really want to rename it then use the lt ctrl gt N command The lt ctrl gt command tells you whether or not the cursor currently has a name and if so what that name is To move the cursor to a previously named node use the lt ctrl gt t command You will be asked for the name of the node to go to of course Reverting to the Previous Cursor Position The lt ctrl gt v command will move the cursor back to where it was just before the most recent major move i e back to where it was before the most recent successful lt
33. h two s because of their special status The property list of any node id contains various properties that describe all nodes of that particular type For example the property list of the atom case contain properties that apply to all nodes that have this as their node id i e all case statement nodes These properties will be described shortly plist atom is an atom formed by gensym which is unique to each particular node That is no two nodes wiii have the same plist_atom The property list of a node s plist_ atom will contain information that applies to that particular node alone For example if the node has a name then it is recorded as a property on that node s plist atom The exact form of contents which completes the representation of a node depends upon whether or not the node is an atomic or leaf node If the node is not atomic then contents is the sequence of sons of the node in order If the node is atomic then contents will be empty or be an atom or a sequence of atoms this depends upon the type of node For example a node for the identifier FOO has the form id plist_atom f oo Nonterminal nodes have the form nonterminal plist_atom non terminal type For example the nonterminal node lt statement gt has the form nonterminal plist atom statement Pattern variable nodes have the form pat ternvar plist atom nonterminal type patte
34. he Ada Implementation Parts of Ada that are Not Supported The following features of the Ada language described in I are not yet supported by the editor G The Ada real number facilities ii Exception handlers although exception declarations and the two forms of the raise statement are supported iii Discriminant declarations and record variant parts iv Derived types v Renaming vi Separate compilation facilities using the reserved word separate vii Representation specification and implementation dependent features Extensions to the True Ada Syntax Usually the editor will only allow structures that conform to the Ada syntax given in 1 That is in general the parser will not accept syntactically incorrect constructs and it is not possible to create such constructs using productions coercions etc However there are a few circumstances where a more liberal syntax is allowed This was done in order to keep the external Ada grammar in the file ADA SYN SLR 1 and also to allow a more useful set of coercions in some situations The changes are i In declarative parts declarative items are not required to precede program com ponents ii Indexed names which can serve as array elements function calls procedure calls when is appended and slices can be more liberal than allowed in true Ada In particular the indices of such names can have the form lt choice list gt
35. hird son represents the statement list that forms the body of the for statement Note that purely syntactic items such as reserved words and semicolons are not represented internally as nodes although such things will of course be displayed on the user s screen The leaves of the tree i e those nodes that have no sons represent items that can be considered atomic in that they have no editable subparts Examples of such nodes are identifiers numbers and nonterminals discussed below The nodes of the tree fall into three classes Firstly there are the ordinary nodes which represent actual programming language structures Most nodes will usually be of this type the for statement node mentioned above would be such a node for instance Secondly there are nonterminal nodes When displayed they are delimited by left and right angled brackets for example lt statement gt These nodes can be thought of as unexpanded placeholders which can later be filled in i e replaced by an ordinary node Nontcrminals serve two related purposes As mentioned above they serve as 4 User Guide placeholders for nodes not yet expanded In addition they help ensure that the program as a whole remains syntactically consistent For example a for statement node could replace the nonterminal node lt statement gt but could not replace the nonterminal node lt expression gt since a for statement is a statement but not an ex
36. identifier gt n all or n lt character string gt depending upon which mnemonic was given The printname property of a nonterminal type is used by the display routines It is formed by exploden ing the nonterminal name For example the printaame property of name is 78 65 77 69 printname properties are also used in leaf nodes such as identifiers and numbers for such nodes the property is set up by the node building routines Print Boxes Information that is to be displayed on the screen is represented by a data structure called a print box This representation is high level in that it is the same no matter what particular terminal is used to display the information Some static print box information is computed once by the preprocessing routines An example would be the information that the reserved word is should follow the case expression whenever an Ada case statement is displayed Such permanent display information is put on the property list of print option atoms during the preprocessing phase Details of the properties of print option atoms will be given shortly Other dynamic print box information i e information that shows what is currently displayed on the screen is computed at runtime by the high level display routines the code for which is in the file TIDSPL EDT A print box can take one of three forms The most fundamental type of print box has the form
37. inimum size constraints not only for the node under consideration but also for the cursor node as well as for the collection of descendants to the left of the cursor and the collection of descendants to the right of the cursor The reason for this is that the display routines consider the size constraints for the cursor node to be more important than the size constraints of the other nodes Also if some ellipsis needs to be done on the nodes surrounding the cursor then the display routines needs this information in order to bc able to assign a fair number of screen lines to the nodes both to the left ard to the right 32 System Architecture of the cursor In this case the maxminsize property of the node s plist_atom has the form mixed the minimum size that the node can be printed in the minimum size of the whole node the maximum size of the whole node the minimum total size of the descendants to the left of the cursor the minimum size of the cursor node the minimum total size of the descendants to the right of the cursor the maximum total size of the descendants to the left of the cursor the maximum size of the cursor node the maximum total size of the descendants to the right of the cursor The property actualsize gives the size that the node s print box given by the print box property takes up when displayed on the screen As before size means
38. ion unit you must first create a new bare node of the appropriate nonterminal type using the lt ctrl gt W command and then parse into this new nonterminal node using the lt ctrl gt P command These commands are described later If no syntax error is found the input program will be displayed on the screen The entire compilation unit will be highlighted indicating that the cursor is now at the root of this new tree There are several files of examples on which you can apply the lt ctrl gt I command The files are TEST1 ADA EDT RSF TEST8 ADA EDT RSF on SAIL Most of these examples are taken from the CACM Ada self assessment test 3 Note that the editor does not assume a default file extension with any of its file I O commands you have to type in the ADA While using the editor it is possible to file away using a command to be described later the node that you are currently editing so that it can be restored during a later session If you do this you are actually filing the internal form of the node rather than the text that the node represents To input a node that was previously saved in internal form use the lt ctrl gt i command As with lt ctrl gt I you will be asked for a file name and a new node name Unlike the lt ctr1 gt I command however a tree input using the lt ctrl gt i command need not be an entire compilation unit The internal tree forms of the compilation units given in the example
39. l gt i and lt ctrl gt I commands enable you to do this If you have an Ada compilation unit e g a package or a subprogram on file in text form you can input it to the editor using the lt ctrl gt I command You will be asked for the name of the file and also for a name to give to the new tree that will be constructed as a result of the input Whenever you create a completely new tree the editor asks you to give a name for it This is done in order to avoid the risk of this tree becoming orphaned at some later stage Since the input file is in text form it is first read by the parser and checked for syntactic correctness Note that at present the editor has no knowledge about semantic correctness If a syntax error is reported there will be one of three possible causes i There may be a genuine Ada syntax error ii The piece of text in question may strictly speaking be legal Ada but a part of Ada of which the editor in particular the parser is not currently aware Appendix B describes those parts of Ada which the editor does not currently support iii The complete piece of text may be legal Ada but may not be an Ada compilation unit For example it may instead be only an Ada statement For the parser to be used it must know exactly what kind of syntactic nonterminal element it is expected to check for For the lt ctrl gt I command compilation unit is assumed If your text file contains less than a compilat
40. ly at the cursor position and inserts the most recently deleted node in its place The original node is then remembered as being the node most recently deleted Adding to a List If the cursor is at an element of a list for example at a statement inside a subprogram body or at a parameter inside a subprogram call then you can add to the list by using the commands lt ctrl gt and lt ctrl gt lt ctrl gt inserts a new nonterminal node just to the left of the cursor and then moves the cursor there Similarly lt ctr1 gt inserts a new nonterminal node just to the right of the original cursor Note that every element of a list is of the same nonterminal type Creating New Nonterminal Nodes If you wish to build a tree from scratch then you will need to obtain a bare root node to start from The lt ctrl gt W command enables you to do this You will be asked for a name to give the new node and also for the nonterminal type of the new node The cursor will move to the resulting nonterminal node Three nonterminal types that will be commonly used are compilation unit statement and expression a complete list is given in Appendix B Note that you do not type any angled brackets around the nonterminal name Invoking the Parser Suppose the cursor is at a nonterminal node which you wish to fill in So far we have described how this could be done by using lt ctrl gt c to insert a copy of some previ
41. ments e g in a loop then lt ctr1 gt will move it to the first statement in that list Note that reserved words such as for and if in the examples above are skipped over since they are not represented as explicit nodes Similarly the lt ctr1 gt command moves the cursor to the rightmost son of the original cursor As with all cursor movement commands it has no effect if there is no such node to move to lt ctrl gt t can be thought of as the inverse of lt ctrl gt and lt ctrl gt It is used to move to the parent of the cursor lt ctrl gt N extends this it moves the cursor to the root of the tree i e the complete item being edited lt ctrl gt moves the cursor to the right brother of the original cursor If there is no immediate right brother then the editor looks for an ancestor that has an immediate right brother and then moves the cursor to that right brother This feature can be very useful As an example suppose that the cursor is at the 3 in FOO BAR 3 BAR BAR 1 Then lt ctrl gt will move the cursor to the statement BAR BAR 1 lt ctrl gt moves to the left brother of the original cursor It behaves analogously to lt ctrl gt lt ctrl gt is used to move to rightmost i e the farthest right brother of the cursor lt ctrl gt C moves to the leftmost brother Unlike lt ctrl gt and lt ctrl gt these commands only consider immediate brothers Note that the application o
42. n must contain at least one element In this way the editor ensures that the hard deletion command lt ctr1 gt D always preserves syntactic correctness The template property is used to specify the nonterminal types that the sons of any node with this node id must have The form that this property takes depends upon the is fist property mentioned above i e upon whether or not such nodes are list nodes If the is list property is non nit then the template property is a one element list whose sole element is the nonterminal type of any son of such a list node For example the template property of the node id statement list is statement Recall that sons of list nodes are homogeneous in that they all have the same nonterminal type If on the other hand the node id s is list property is nil then the template is a list giving the nonterminal type that each of the node s sons must have Each element of this list is the nonterminal type of the corresponding son For example the template property of the node id for an Ada assignment statement is name expression This indicates that nodes have two sons the first being a name with the second being an expression 26 Svstem Architecture The cmenulist property specifies the possible coercions that nodes with this node id can undergo i e by the use of the lt ctrl gt q command If no coercions are possible then this property is nil Otherwise the property is a list
43. n typing ife the appropriate mnemonic The cursor is then transformed into an if statement with an elsif and or else part as illustrated An embedding is a similar concept An embedding embeds an expanded node as one of the sons of another node of the same nonterminal type In other words another node of the same nonterminal type as the cursor node is grown around the original cursor node As an example an embedding allows you to easily attach a label to an expanded Ada statement a node representing a labelled statement is created with its second son being the original statement Its first son will be an lt identif ier gt nonterminal for the label Embeddings are most usefully applied to expressions if for example you have constructed X and then decide that what you really wanted was X Y Z If you are at an expanded node then you can see the embedding menu by typing lt ctrl gt E The appearance of the pattern variable cursor in an embedding menu entry indicates where the original cursor node would be placed as a result of the embedding To select an embedding from the menu type lt ctrl gt e mnemonic lt cr gt Before while whilel gt O loop i X X F D l l end loop After lt ELSIF ELSE PART gt Figure 2 An example of a coercion User Guide 15 Patterns and Search Commands The editor has powerful facilities for searching and replacement It is pos
44. nclosing list smaller than it is allowed to be The reason that hard deletions are allowed in lists is of course because they preserve the syntactic integrity of the program fragment being edited This would not in general be true if hard deletions were allowed elsewhere However there are circumstances where it would be desirable to be able to perform hard deletions elsewhere than inside a list but still preserve syntactic correctness Two examples would be the deletion of the closing identifier of a subprogram or package and the deletion of the private part of a package specification Unfortunately the editor does not allow you to perform this kind of hard deletion with a single command Such deletions can still be performed though by performing an appropriate coercion on the parent of the node in question Coercions will be described later If a node that was previously named is soft or hard deleted then the deleted node retains the name that it was previously given and in the case of a soft deletion the replacement nonterminal node is initially unnamed This allows you to name a subnode of the tree being edited chop it off and then come back to it at some later stage as well the undeletion facility mentioned in the next paragraph allows you to restore the node that was most recently deleted There is an exception to this rule however If the root of the tree being edited is deleted then it is the resulting nontc
45. nd p have the same node id node ids are described in section 3 Informally it means that n and p look exactly the same when displayed in full on the screen ignoring how their sons are displayed For example n and p could both be for statements although if the discrcte range of one is preceded by reverse then the discrete range of the other must also be preceded by reverse Also n and p could both be assignment statements or could both bc expressions and so on or b p is a pattern variable of the same nonterminal type as n and if the pattern variable p was previously bound to another node m n and m are identical analogous to EQUAL in LISP If p was not previously bound to another node and p and n have the same nonterminal type then p can be considered as being bound to n from here on ii n and p have the same number of sons This will automatically be true if n and hence p is not a list node iii Considering the sons if any of n and p in order each son of n matches the cor responding son of p Note that as a consequence of this rule if p is not a pattern variable and does not contain any pattern variables then n matches p if and only if n and p are identical nodes For example the assignment statement FOO FOO BAR matches both the pat ten X X Y and the pattern X Y Z but the statement FOO BAR MUMBLE matches only the second pattern It should be noted that the above
46. nnot be displayed without some nodes being elided i e if the maximum print size of the root exceeds the size of the screen In this case the following steps are performed i owtermost node is found This is the node that is to be displayed outermost on the screen This will be the root unless this is impossible in which case we select the highest ancestor of the cursor that can be displayed and whose node id has a printable property of t ii cursorguide is calculated cursorguide is a guideline size for the cursor See the routine find_cursorguide in the file TIDSPL EDT to find out exactly how cursorguide is calculated iv leftguide and rightguide are calculated These are the guideline sizes for the portion of the tree to the left and to the right of the cursor node respectively leftguide is calculated by the routine find_leftguide rightguide is found simply by subtracting leftguide and cursorguide from the size of the screen v If owtermost node is in fact the cursor node then it is printed using the routine print_cursor Otherwise the routine print_mixed is used to print the node outermost_ node using the guideline sizes mentioned above 36 Appendix A Summary of Commands Appendix A Summary of Commands File Input Commands lt ctrl gt i Input a previously saved tree lt ctrl gt I Input a text file must be a compilation unit Basic Cursor Movement Commands lt ctrl gt Leftmost son
47. node building routines both created by the preprocessing phase to parse input text and produce a tree structure as output The final two components are not present when the editor is running but are used to bring up the editor for the first time The language description files provide the editor with the necessary information about the programming language that it supports The files contain information about both the external language grammar that is used by the parser and the internal tree format that the editor uses directly The final component is the preprocessing part which enables the language description files mentioned above to be preprocessed into a form that can be used by the parser and the editor kernel The following two diagrams show how the many different modules that make up the editor can be grouped together to form the five components mentioned above The first diagram shows the first three components these three being the components that are present when the editor is running The arrows indicate major control flow within the editor an arrow from one module to another indicates that the function pointed to by the arrow is frequently called from within the first module The second diagram shows the language description files and the preprocessing part Note that the diagrams assume that the programming language supported is Ada However if another language were supported the only change would be that the fil
48. of coercion descriptors There is one descriptor for each possible coercion Each descriptor has the form mnemonic coercion map mnemonic is the mnemonic that will appear when the coercion menu is displayed i e it is the mnemonic that the user can enter after applying the lt ctrl gt q command The coercion map is a list the car of which is the node id of the new node that will result from the coercion The cdr is a list of non negative integers which indicates how the sons of the new node will be made up from the sons of the old A 0 indicates that the corresponding son of the new node will be a nonterminal node A positive integer n indicates that the corresponding son of the new node will consist of the nth son of the original node As an example the cmenulist property of while loop 1 which is the node id for an Ada while statement without an attached loop identifier is id while loop 2 0 1 2 0 loop basic loop 1 2 for for loop l1 0 0 2 forr forr loop l 0 0 2 Gf lif i 2 ife life 1 2 0 block block 2 dblock dblock 0 2 Consider for example the fifth element of this list if lif 1 2 This means that if the cursor is at a while statement then the coercion command lt ctrl gt q if lt cr gt will transform the cursor node into an if statement The first son of this if statement i e the conditional expression will be the first son i e the conditional expression of the while statement The
49. operty of a node id is the property printable This property is t if it would be okay for nodes with this this node id to be the topmost node that is displayed on the screen should it not be possible for the root of the tree to be displayed Of course if it is possible to display the root on the screen as is almost always the case then the root will be displayed even if the root s node id has a printable property of nil Properties of Nonterminals A nonterminal type such as identifier and statement has various properties that apply to all nodes of this particular nonterminal type Like the properties of node ids these properties are given along with the nonterminal types themselves in the language description file ADA INT and are assigned to the nonterminal types during the preprocess ing phase The properties given to nonterminal types are is_nonterminal pmenulist emenulist and prin tname The is_nonterminal property is set to t for every nonterminal type This property is used only in the implementation of the lt ctrl gt W command which creates a new isolated nonterminal node to check that the atom that the user types at the keyboard is really a nonterminal type The pmenulist property specifies all possible productions on the nonterminal in ques tion The property takes the form of a list of dotted pairs The car of each pair is the mnemonic for a production and the cdr of the pair is the node id of the node
50. ously named node or by using lt ctrl gt u to undelete the last node that was deleted However neither of these commands is of any help to us if we want to expand the nonterminal into something new You can do this by using productions described later by reading a piece of program text from an input file or by entering text from the keyboard The last two of these require that the text be checked by the parser since the editor must maintain syntactic correctness at all times If you wish to fill in a nonterminal node by typing text from keyboard use the lt ctrl gt p command You will be prompted by a User Guide 11 gt at the bottom of the screen Type in the text it can be over more than one line if you wish and then type lt altmode gt lt cr gt Admittedly this is a bit of a nuisance but the parser needs a symbol to represent end of file lt altmode gt serves this purpose If the parser detects a syntax error in your input then an error message will appear and no action is taken Otherwise the nonterminal will be filled in by a node representing the text that you typed in It is also possible to fill in a nonterminal node with text from an input file using the lt ctrl gt P command You will be asked for the name of the input file The parser will check the text in the file as it does with lt ctrl gt p Note how this command differs from the lt ctrl gt I command which assumes that the text in
51. pression Thirdly there are pattern variable nodes These nodes are used for searching and replacement which are described later gt The following diagram illustrates the top branches of the internal tree form for one particular Ada for statement The editor s internal tree structure is described in more detail in section 3 The Cursor At any one time there is one particular node in the tree that can be edited by the user This distinguished node is the cursor node Virtually all of the editor commands apply to this one node either to change it in some way manipulating the cursor or to make some new node the cursor node moving the cursor On the user s screen the text represented by the cursor node and all descendants of this node is emphasized relative to other surrounding text The exact nature of this emphasis is terminal dependent On DataDise terminals reverse video is used On Datamedia terminals the pixels of the cursor text characters are are dispiayed brighter than those of the characters of surrounding text An Alto running TALK displays the cursor in reverse video however Throughout this report the term cursor is used to refer both to the internally represented cursor node mentioned above and to the text represented by this node which appears highlighted on the user s screen Which of these two meanings is intended will usually be clear from the context in which the term appears
52. re mnemonic is the mnemonic to the left of the appropriate entry in the menu The cursor will then be filled in by a copy of that menu entry If you wish you can type the number that appears at the far left instead of the mnemonic Of course if you can remember the mnemonic that you want then you can use lt ctrl gt e or lt ctrl gt q without looking at the menu If there is only one possible production for the nonterminal in question then the production will be performed without you being asked for a mnemonic This frequently applies to list nonterminals such as lt statement list gt and lt declarative part gt The editor will fill in such nonterminals with the appropriate list node containing two non terminal sons This number of sons two is arbitrary and of course you can later go down into the list and either decrease the number of sons using lt ctrl gt D or increase the number of sons using lt ctrl gt or lt ctr1 gt 12 User Guide lt ctrl gt C will erase any menu that is displayed and will give you the normal display window again Any other non menu command will also delete the menu and restore the original display but lt ctr1 gt C is useful if you just want to restore the display without doing anything else If a menu cannot fit entirely on the screen then you can scroll forward using the lt ctr1 gt command or scroll back using the lt ctrl gt command A highlighted message will appear at the
53. re will be no ellipsis in the output even if some subnodes happen to be elided on the display when the lt ctrl gt Q command is given When using this command you will be asked to choose between SCRIBE output and plaintext i e normal output The former choice is useful if you want to later make a pretty printed hardcopy using the SCRIBE program The lt ctrl gt o command outputs the tree to a file in internal tree form Both of the above commands can be used even if the tree that you wish to output contains nontcrminals or pattern variables although if you use lt ctrl gt 0 to file away such trees then you won t be able to read them back later with lt ctrl gt I or lt ctrl gt P Note that in contrast to most of the other commands which apply only to the cursor the lt ctrl gt o and lt ctrl gt 0 commands output the entire tree that is being edited Coercions and Embeddings It is possible to manipulate an expanded node in any syntactically legal way by using User Guide 13 the commands that we have described so far However coercions and embeddings allow you to perform some of the more common manipulations far more easily A coercion performs an immediate transformation of an expanded node into another kind of node For example a normal if statement can be transformed into an if statement with elsif parts or an else part or both An if statement can also be transformed into a while statement A gt e
54. rminal node that retains the original root s name The reason for this exception is that the entire tree will usually be deleted only to correct an error In such circumstances it would be most desirable for the root s name to be retained by the nonterminal and thus by any correction that follows The editor remembers the last node that was deleted by either lt ctrl gt d or lt ctr1 gt D At any later stage you can undelete this node if you are at a nonterminal node of compatible type in particular you can immediately undo a soft deletion You do this by typing lt ctrlou As with lt ctrl gt c this inserts a copy of the node that was most recently deleted This means that you can USC lt ctrl1 gt u several times at different instances of the compatible nonterminals In each case a copy of the same last deleted node will be inserted in place You cannot undo the effect of a hard deletion immediately although 10 User Guide you can still undo a hard deletion by inserting a new nonterminal node to the left or right of the resulting cursor position using the lt ctrl gt or lt ctrl gt commands to be described later and then using lt ctrl gt u Finally suppose that you wish to simultaneously delete a node and undelete a pre viously deleted node in the same place You cannot do this with any of the commands so far described The lt ctrl gt U command allows you to do this This command deletes the node that is current
55. rn variable id As an example consider the Ada expression FOO in 1 12 or FOO gt 100 This expression would be represented internally as tor g0106 in g0109 id g0113 f o o num g0114 numi num g0115 num12 gt g0121 id g0119 foo num g0120 numt00 Note that the gensym numbers that I have chosen for the plist_atoms are arbitrary They will always be distinct however yn Properties of node ids Each node id has a number of properties that describe various features common System Architecture 25 to all nodes having this node id These properties are given along with the node ids themselves in the language description file ADA INT and are attached to the node ids during the preprocessing phase The properties are possible nonterminals is_atomic_ node is_list template cmenulist print format always_0_indents always nil context nodes not below and printable They are described in detail below The property possible nonterminals is a list of all possible nonterminal types to which nodes with this node id could belong Many node ids have only one such nonterminal type the possible nonterminals property of the node id case is statement for ex ample On the other hand the possible nonterminals property of and is expression parameter choice since an and expression can occur as a parameter of a procedure and function call and also as a choice in a case statement as well as in pla
56. second son of the if statement i e the list of statements following then will be the second son of the while statement i e the list of statements following loop The print format property is the most complicated property that node ids have It describes all the possible ways that nodes with this node id can be printed It should be noted that when a node is printed it is printed in a particular context This context is given as a LISP atom The default context is nil and most of the time nodes are indeed printed in a context of nil In particular the root is always printed in a context of nil Sometimes however nodes will be printed in different contexts depending upon their surroundings Consider for example the expression x y If this expression does not appear inside another expression then it will be printed in the default context i e nil If this expression appears as one of the terms of an additive operation then it will be printed in the context term If however this expression appears as a factor in a multiplicative operation or an exponentiation operation then it is printed in the contexts factor and primary respectively In such a case the expression should be printed surrounded by parentheses the parenthesis of expressions is the main example of a situation where context is important The print format property of any node id consists of a list of one or more context options A con
57. sible to specify any named node as being a search pattern and to search for occurrences of that pattern in the original tree It is also possible to specify another node as being the replacement pattern and to replace an occurrence of the first pattern by an appropriate instantiation of the second pattern Any named node can be used as a pattern although patterns will usually be nodes that are standing alone A pattern will typically be created using lt ctrl gt W and built up with productions lt ctrl gt lt ctrl gt p and or lt ctrl gt T the lt ctrl gt and lt ctrl gt T com mands will be described shortly Patterns frequently have pattern variable nodes as sub nodes Actually pattern variable nodes can appear inside any tree but as will be ex plained below they are really only useful inside patterns Pattern variable nodes are atomic nodes and are displayed as id where id is some symbol A pattern variable node can be created from a nonterminal node by using the lt ctrl gt T command You will be asked for an id for the pattern variable this can be any sequence of visible characters but not containing characters such as or which all mean special things to the LISP reader To initiate a search for an occurrence of a pattern shortly we will explain exactly what it means for a node to match a pattern use the lt ctrl gt w lt ctrl gt f or lt ctrl gt s
58. splayed should this serve to increase the displayed size of the cursor The lt ctrl gt R command will cause the screen to be rebuilt and redisplayed from scratch This command can be used as an escape hatch should the screen ever get messed up in some way Aborting a Command If you mistakenly type a command that asks for more input before taking effect you can abort it at this stage by typing lt ctrl gt g This is in fact a LISP command which exits to the top level of LISP Provide that the editor is operating normally no command should cause an infinite loop Should an infinite loop appear to be occurring however you can interrupt the editor on SAIL by typing lt esc gt i This should interrupt the editor At this stage you can type lt ctrl gt g and then lt ctrl gt R to restore the display User Guide 19 Halting the Editor The command lt ctrl gt z will halt the underlying LISP system and will therefore halt the editor as well Should you happen to type lt ctrl gt z accidentally you can resume the editor by typing REENTER lt cr gt to the SAIL monitor and then TERMINAL INITIALIZE gt lt cr gt and lt ctrl gt R to restore the display 20 System Architecture 3 System Architecture This section of the Reference Manual serves two purposes Not only does it provide details of the architecture of the system that may be of general interest but also it gives further d
59. suffix of this sequence that does not contain the cursor or any of its descendants Note that as a consequence of this o does not contain any ancestors of the cursor Then g is the sequence of nodes that will be traversed in a search after the cursor Note that this order too is natural Having performed a search once you can repeat the search any number of times without having to retype the search pattern name each time lt ctrl gt V that s a logical or sign not a V repeats the most recently performed search searching inside the cursor lt ctrl gt gt repeats the most recent search searching after the cursor lt ctrl gt 2 repeats the most recent search searching first inside the cursor and then after it if the inside search 16 User Guide was unsuccessful Note that unlike the lt ctrl gt w and lt ctrl gt s commands the lt ctrl gt v and lt ctrl gt 2 commands do not check the cursor itself because they are typically used immediately after a successful search To make it easier to remember these commands note that the characters v gt and 2 appear above w f and s respectively on the SAIL keyboard We shall now explain what it means for a node to match a pattern match can be defined recursively as follows A node n matches a pattern p if the following three conditions hold i Either a n and p are the same sort of node Formally this means that n a
60. syntax of the programming language to be edited EDT can be reconfigured to provide syntax based editing for that particular language This is described in more detail in section 3 Currently one such programming language is supported the programming language Ada although the complete Ada language is not yet supported The resulting Ada editor is called ADAEDT The remainder of this manual can be thought of as describing this particular editor However it should be remembered that most of the manual would still apply if the editor were reconfigured for another language The best languages for this editor would be those with a rich set of possible syntactic constructs Ada and COBOL for example Languages such as LISP which has a very parsiminous syntax would be less suitable Three of the major considerations that influenced the design of the system were i Naive users It was anticipated that many of the users of the editor would be un familiar with the syntax of the language that is being used Ada in this case The editor provides menus to help the user select the correct syntactic construct to use ii Modularity The terminal screen and operating system dependent portions of the editor are clearly separated from the rest of the system The editor generates a terminal independent internal Lisp data structure to denote what is to be displayed on the screen Low level terminal dependent display drivers then work from this data s
61. t is an Ada if statement is always printed the same way regardless of the context in which it appears Of course one or more of the descendants of an if node may be elided depending upon the space available but the if node itself will always appear the same The print format property of is factor primary g0135 allbut factor primary g0136 This specifies that if a node is printed with a context of factor or primary then it will be printed surrounded by parentheses Otherwise it will be printed with no surrounding parentheses In both of the examples above there was only one print option atom in each context option It is possible for there to be more than one print option atom in a context option In such a case the editor will choose from amongst these different options based upon the space available on the screen This provides a way to specify one or more concise printing options to use if space on the screen is scarce In fact this capability is not used in the Ada language implementation where any necessary display condensation is provided by eliding in a standard way appropriate elements of statement lists and or declaration lists The properties always_O_indents and always nil context are used so that the display can be updated more efficiently in certain circumstances A great many editor commands alter the structure of the cursor node in some way but do not move the cursor Ideally
62. tains the main display window and the menu window as a result of the execution of a command It should be noted that this code does not assume any particular kind of terminal Virtually all of the command functions in COMINT EDT invoke the routine mainscreen_update This is the main routine in TIDSPL EDT It checks whether or not a change needs to be made to the display and if so causes the invocation of appropriate low level terminal dependent display routines to effect such a change Further details of the display algorithm used by mainscreen_update and its subsidiaries are given later in this section TIDSPL EDT also contains other routines that are invoked by the command functions in COMINT EDT display_menu is used to display a production coercion or embedding menu in the screen s menu window which will cover the main display window forget_current_image helps to implement the lt ctrl gt R command that refreshes the display enlarge_cursor_1 and enlarge_cursor_2 help to implement the display oriented commands lt ctr1 gt j and lt ctrl gt J rcspectivcly INIT EDT contains code that initializes the editor s global variables when the editor is set up MISC EDT contains a few miscellaneous routines The documented source code contained in the files mentioned above those with extension EDT is given in full in the Implementation Guide The file containing the low level display routines will differ depending upon the type of
63. terminal that is supported For DataDiscs the file is DDDPY For Datamedias it is DMDPY The four main low level routines are highlight replace simple_update and draw highlight and replace are used whenever possible since they do not entail redrawing the entire screen but instead only the part of the screen where the cursor is displayed simple_update puts any changes made by highlight and replace into effect draw redraws the entire screen 24 System Architecture The Editor s Internal Tree Form Every node including nonterminal nodes and pattern variable nodes is represented internally in the form node id plist atom contents where contents can be empty node id is an atom which gives the specific type of the node For example it is if for an if statement package body for a package body and for an expression of the form z and y and so on There is a fixed number of these node_ids one for each particular type of node possible The set of possible node ids depends upon the actual programming language that is supported of course This set of node ids is given along with other information in the language description file ADA INT In the current version of the editor supporting Ada there are 133 different node ids For clarity the name of each node id begins with the character Nonterminal nodes and pattern variable nodes have node ids of nonterminal and patternvar respectively These node ids begin wit
64. text option consists of a context specifier followed by a sequence of one A rana ree er Pe er E AA AE ee ee Eh ero ama System Architecture 27 or more print option atoms Admittedly this sounds complicated but in actual practice the print format property of most node ids has the simple form all print option atom Thatis there is usually just one context option with all as the context specifier and with only one print option atom More generally though a context specifier can take one of three possible forms i all This indicates that the following print option atoms can be used regardless of what context the node is printed in ii a sequence of one or more contexts This indicates that the following print option atoms can be used if the node is printed in a context that appears in the aforementioned sequence i allbut a sequence of one or more contexts This indicates that the following print option atoms can be used if the node is printed in a context that does not appear in the aforementioned sequence A print option atom is an atom that is constructed by gensym during the preprocess ing phase Such atoms have various properties that specify in detail a possible way that a node with the node id in question can be printed These properties are described later For examples of print format properties consider the node ids if and The print format property of if is a11 g0070 Tha
65. the input file is a compilation unit and which creates a completely new isolated node rather than filling in an already existing node It should be noted that the parser does not recognize nonterminals in any text that it reads whether or not they are surrounded by angled brackets In particular the program text in a file that is read using the lt ctrl gt I or lt ctrl gt P commands cannot contain unexpanded nonterminals The parser does not recognize pattern variables either Productions on Nonterminal Nodes Most nonterminals can also be filled in using productions These allow you to choose a skeleton of an expanded node from a menu and use this skeleton to fill in the nonterminal If the cursor is at a nonterminal node then the production menu can be displayed by typing either lt ctrl gt E or lt ctrl gt Q If the menu is empty you cannot use productions This only applies to nonterminals such as lt identifier gt which can be filled in only by typing at the keyboard using lt ctrl gt p Note that the editor will display identifiers in upper case regardless of how they are typed in Ada reserved words are displayed in lower case Each entry in the production menu represents a possible substitute for the nonterminal that appears at the top of the menu To the left of each entry is a number and a mnemonic To select an item from the menu type lt ctrl gt e mnemonic lt cr gt or lt ctrl gt q mnemonic lt cr gt whe
66. the number of lines taken up by the node minus 1 Properties of Print Option Atoms Each print option atom which appears inside the print format property of a node id has various properties that describe in detail one particular way to display nodes with that node id The set of properties that cach print option atom has depends upon whether or not such nodes are list nodes i e on whether or not the node id s is list property is nil For list nodes the properties are prefix prefix indents separator separator_ indents suffix suffix_indents ellipsis ellipsis_indents context when_empty and when empty indents These properties are now described using the print option atom g0066 as an example This is the sole print option atom occurring inside the print format property of the node id statement list The prefix property is a list the car of which is a print box for the prefix of the list That is this print box is printed before any element of the list is printed The edr of the list is either nil if the first son of the list is not to be indented relative to the prefix or is an integer n if the first son of the list is to be indented by n units relative to the prefix The property prefix indents is a non negative integer giving the total number of indentations not the size of any indentations that occur in the prefix plus 1 if an indent was specified by the cdr of the prefix property This property which could
67. tive items A declaration but not of a package body subprogram body or task body The item that follows the in an object declaration This will be a type name or an array specification An array index specification A procedure specification or a function specification The list of formal parameter declarations that ap pears inside a subprogram specification A procedure function name this can be a character string The part that follows the word record in a record declaration The declaration of a record component The optional elsif and or else part of an if statement A list of elsif items A clause of the form elsif lt expression gt then A choice in a selective wait statement Like a select option except that it does not in clude when clauses The list of generic parameter declarations for a generic subprogram or package declaration The definition of a type that is given as a generic parameter A list of case items A branch of a case statement 40 Appendix B The Ada Implementation choice list choice identifier list identifier name list name parameter list parameter A procedure function actual parameter or an array index discrete range character string expression Appendix C References 41 Appendix C References 1 Reference Manual for the Ada Programming Language Proposed Standard
68. tors use knowledge of the syntactic structure of the programming language to provide high level language specific editing facilities According ly the user can be freed from much of the drudgery that often accompanies program de velopment such as having to make sure that his program is correctly indented and that no end s have been omitted In addition syntax errors can be eliminated entirely since such editors will usually allow only syntactically legal constructs Some systems also perform semantic checking Probably the most well known example of such an editor is the Cornell Program Synthesizer 2 an editor for programs written in PL CS an instructional dialect of PL I Much has been said about the desirability of a uniform programming environ ment incorporating powerful language specific tools to facilitate program development and maintenance A syntax based editor could be such a tool and could be integrated with other tools such as a debugger an interpreter compiler and a verifier This report describes EDT a syntax based program editor developed for the Program Analysis and Verification Group at Stanford This editor is written in MACLISP It is unlike the Cornell editor in that it is not hard wired to support any one programming language Instead the architecture of the EDT system and indeed the user commands for the system do not presuppose the language to be edited By incorporating files that describe the
69. tructure iii Interface with other tools Internally the editor uses a tree to represent what is being edited The editor could be used as the front end to another tool such as a compiler Ada is a registered traticmnrk of the U S Department of Defense 2 Introduction Any such tool would work directly from this internal tree form Thus the internal format should be flexible enough to be able to incorporate any extra information that the back end tool may require Section 2 of this report can be thought of as the user manual proper in that it describes how to use the editor but does not discuss implementation details Section 3 describes the architecture of the system display algorithms internal formats etc A separate manual the EDT Implementation Guide contains even more details of the implementation including much of the source code This work was supported by the Advanced Research Projects Agency U S Depart ment of Defense under contract NOO 039 82 C 0250 User Guide 3 2 User Guide Running the Editor The editor currently runs only on SAIL supporting a moderately large subset of the programming language Ada At present two kinds of display terminal can be used to run the editor DataDiscs and Datamedias To use the editor on a DataDisc terminal type R ADAEDD If you are on a Datamedia terminal or an equivalent terminal such as an Alto running TALK or DMCHAT type R ADAEDM This D
70. ven by the following son specifier element is not to be indented or if the filler is the last element of the list or is a non negative integer indicating that the following son is to be indented by m units n is an integer giving the total number of indents that occur in the print box b plus 1 if m is non nil n could of course be computed directly from b and m A son specifier has the form s c s is a non negative integer c is a print context in particular it can be nil If s is non zero then it indicates that the sth son of the node is to be printed in a context of c If s is zero then the son specifier just serves as a placeholder between two adjacent fillers and thus c is irrelevant The property total indents is the total number if indents that are specified in the print format property As an example consider the node id if This node id has a single print option atom g0070 occurring in its print format property The print list property of g0070 is O string 4 105 102 32 1 1 string 4 32 116 104 101 110 1 2 1 indent 0 0 string 4 101 110 100 32 105 102 59 34 System Architecture That is an if node is printed in the Following way Firstly the string if is printed Note the space after the letter f Then the node s first son i e the conditional expression is printed in a context of nil Thirdly the string then is printed The secon
71. xpression can be transformed into a lt and so on If the cursor is at an expanded node as opposed to a nonterminal you can see the coercion menu by typing lt ctr1 gt Q Recall that if you are at a nonterminal then lt ctr1 gt Q and lt ctr1 gt E will give you the production menu for that nonterminal Each entry in the coercion menu shows a possible way that nodes of the form given at the top of the menu can be transformed coerced into nodes of another form Items of the form number are pattern variables and are used to denote the sons of the original node Whenever such pattern variables appear in a coercion menu item it means that after the coercion the corresponding son of the original node the actual son not a copy will be inserted in its place Pattern variables are also used in a similar way for searching and replacement to be described later To select a coercion from the menu type lt ctrl gt q mnemonic lt cr gt Two common uses for coercions are adding an identifier to or removing one from a block or loop statement and adding an initialization part to or removing one from an object declaration or a package body The node that results from a coercion will retain any name that was held by the previous node The following diagram illustrates a coercion of a while statement into an if state ment This coercion could be performed by moving the cursor to the while statement typing lt ctrl gt q and the

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