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1. jC A LALR 1 Parser and Lexical Analyzer or for JavaScript written in JavaScript Version 0 30 User s Manual Release date November 20 2008 Copyright O 2007 2008 by Jan Max Meyer J M K S F Software Technologies 44265 Dortmund Germany http www jmksf com jscc lt at gt jmksf lt dot gt com SOFTWARE TECHNOLOGIES JS CC User s Manual Page 1 of 34 Table of Contents Tntrodueing JS CC oi Ge eine eer Rolain RE 3 Wacome toJS CC Earra R a E T OO TA A OS 3 The intention behind JS GG ax eren E E E E NEA Ee 4 Changes on this COCO rOenmaHIG naaa bned a ktag ay d vhaa ada 2 aT Sad Oo azag dK aata 4 Future Pla iii A Ae li 4 SOME Words by Heat rica A E ad AE 5 2 A quick Star example A A A do 6 BuIdINg ETA a den 6 Installation and artUDiiuiiiio na A a A et de 7 Amexample parse livcccs 3 rcrscedeeaes tah tried Ee deca acces dedito lada tanda dlls beste dada 9 Compiling the Tnne TTT 11 3 The Grammar Definition Language eee eee eee 12 Generals LAA al Ea L theca ha O A ba ANKE 12 The Terminal Declaration Part lt azez ieat aaa aaiae aaa cnn rra rn cnn 12 Regular Expressions imor a dida 12 Ambiguous Regular 2 STT cnn naar nn rra rc rnnnnnnrcncnnnnn 13 Associativity and Precedence ccoo a ee 14 WINE PICS a mnd Si 14 The Grammar Definition Par TTT 15 Accessing right hand side items in semantic actiON oooonnoncccnnnnnnnonccccncnnnconnnnnccnnnnrn cnn cnc naar nn cnn rr nnnnnnnn 15 Valde TYPOS tt 16 Resolving COM2. JS CC is an open source project released under the terms and conditions of the Artistic License When coding JS CC started in 2007 it was just planned as a quick and dirty fun project of implementing a LALR 1 parser generator in JavaScript for educational purposes but it rapidly grew up because tons of more useful features where added trough the time that are making it a productive and usable system for parser construction and for educational issues The most amazing thing featured by this software is that JS CC is capable to build a complete working compiler for any context free language from a grammar specification with embedded semantic code segments within a standard web browser like Mozilla Firefox Since the first public release v0 24 of JS CC many things have changed in this project It received recommendations and accolades people started to use it for production and academic issues and some fixed bugs and ported it to other platforms First focused on Windows with JScript as default platform for the console version of JS CC the project s maintenance system changed over to Linux Windows will still be supported but core development is done on Linux now and in future Changes on this documentation For those who already read the last version of this manual delivered with JS CC v0 26 you will see that much changes where made and the documentation contains lesser pages than the previous one Many mistakes had been correcte
3. The only Makefile optimized for Windows nmake is Makefile jscript all the rest uses GNU make under a nix environment JS CC User s Manual Page 6 of 34 Installation and Start Up To install JS CC download the Tarball or Windows setup program By unpacking installing it you get a pre configured JS CC environment which uses Mozilla Rhino Tarball or Microsoft JScript setup The web environment can be used from both editions and any operating system To build JS CC for other platforms read the build howtos in the according Makefiles After you successfully built JS CC run it with your desired platform Under windows you can simply run jscc exe or cscript Nologo jscc js Shell Konsole Session Edit View Bookmarks Settings Help make f Makefile rhino rhino _jscc_rhino js v o jscc_parse js p jscc t driver_rhino js_ jscc_par se par 3scc_parse par produced 49 states 37 shifts 212 reductions 56 gotos O warning O error rhino _jscc_rhino js v 0 jscc_regex js p regex t driver_rhino js_ jscc_re gex par 3scc_regex par produced 25 states 40 shifts 169 reductions 49 gotos O warning error cat jscc_global js jscc_debug js jscc_first js jscc_printtab js jscc_tabgen js j scc_util js jscc_bitset js jscc_integrity js jscc_lexdfa js jscc_lexdbg js jscc_ parse js jscc_regex js jscc_rhino js jscc_main js gt scc S rm jscc_parse js rm jscc_regex js Compilation succeeded ed ii rhino jscc js u
4. function letvar vname value var i for i 0 i lt v names length i E manesi nto tringo vianes tos trang N JS CC User s Manual Page 22 of 34 break Tf as Same se length v names push vname v values pus 00 v_values i value Function to get a variable s content over its name function getvar vname var i for i 0 i lt v names length i Ea vomamesi i toString vriame toString return v_values i return 0 This is the interpreting function working on base of the compiled program structure function execute node var ret 0 if node return 0 switch node type case NODE_OP switch node value case OP_NONE OP NONE can have childs if node children 0 if node children 1 break case OP_ASSIGN letvar node children 0 break case OP_IF if execute break JS CC User s Manual a block node children 0 node children 1 node children 1 node children 0 node children 1 Page 23 of 34 JS CC User s Manual case OP IF ELSE if execute node children 0 else break case OP WHILE DO while break case OP_DO WHILE do while break case OP_WRITE execute node children 1 execute node children 2 execute node children 0 execute node children 1 execute node children 0 execute node children 1 WScript Ech
5. loops and conditional execution as well as variables As variable type only numbers are supported integer and floating point all use the same internal JavaScript type Number The Definition of user defined functions is not possible in this scripting language but it would be a thing of simplicity to add this feature For text output XPL provides a special say command which allows to output constant texts To get familiar with XPL s syntax look at the following example scripts hello xpl This is a simple Hello World script written in XPL say Hello World 99 bottles of beer xpl The wonderful 99 bottles of beer program bottles 99 do The output will not be the prettiest but that is limited by the implementation you can change it if you want write bottles if bottles 1 say bottle of beer on the wall else say bottles of beer on the wall write bottles if bottles say bottle of beer else say bottles of beer say Take one down pass it around bottles bottles 1 write bottles if bottles 0 say no more bottles of beer on the wall else if bottles 1 say bottle of beer on the wall else say bottles of beer on the wall SA Tiy Empty line while bottles gt 0 say That s TEUR JS CC User s Manual Page 18 of 34 countdown xpl A rocketry launch countdown 7 Say The tinal countdown progam do say Enter your start
6. CS aci A ade O 16 4 Implementing a scripting 1anguage see eee eee eee eee eee 18 MACHA TTT 18 Defining th gramma s danene a a be Janne ie AL ie 19 Executing the ee did 21 The enie SOU Cierra pil OES 21 Belz sle linis PASES un A A e o dre a 29 EEE O 29 Debug FACING Sissies ed a EEE EN 30 Debugging with the Web Environment sss es sees eree e resse eee eee eree rees ereer 31 License Agreement binds cece te tigre ti A AAA A ee 32 Te T GM Ge ee EAEE 34 JS CC User s Manual Page 2 of 34 1 Introducing JS CC Welcome to JS CC JS CC is the first available parser development system for JavaScript and ECMAScript derivatives It has been developed both with the intention of building a productive compiler development system and with the intention of creating an easy to use academic environment for people interested in how parse table generation is done general in bottom up parsing JS CC is a platform independent software that unions both A regular expression based lexical analyzer generator matching individual tokens from the input character stream and a LALR 1 parser generator computing the parse tables for a given context free grammar specification to build a stand alone working parser The context free grammar fed to JS CC is defined ina Backus Naur Form based meta language and allows the insertion of individual semantic code to be evaluated on a rule s reduction JS CC itself has been entirely written in JavaScript so it can be
7. case insensitive and program structure operators ip ELSE WHILE po say WRITE READ JS CC User s Manual Page 25 of 34 AA PAS A E Identifier A A String ces Integer OSA OS MOS MOSS Float 7 Operators to be used in expressions gt tt Program Stmt Bast Stemt JS CC User s Manual UE U L U Program Stmt F SeMt List Stnt F Expression Stmt IF Expression Stmt ELSE Stmt WHILE Expression DO Stmt DO Stmt WHILE Expression SAY String y WRITE Expression READ Identifier Smatch Smatch execute ode de I de ode I oe oe I de ode I oe oe I de de I oe ode I de de I match substr 1 Smatch length 2 match replace g yen y a ES createNode NODE_OP OP NONE 1 2 createNode NO OP IF 2 createNode NO createNode NO createNode NO 2 54 createNode NO pe createNode NO me AN createNode NO OP IF ELSE 2 OP WHILE DO 2 DE OP DE OP pee o P DO WHILE OP SAY OP WRITE OP READ Page 26 of 34 pe Identifier Expression createNode NODE OP OP ASSIGN Se senest 2 tera SSS icreateNode NODE OP OP NONE all Expression Expression Expression ase CreaeeNode NODE OP OP
8. to the grammar most simple expressions will return the right result e g 2 3 but in expressions like 4 4 5 the result will be wrong because trough our precedence rules for multiplication the generated parser parses 4 4 5 instead of 4 4 5 To resolve this problem we need to attach a higher precedence level to the production for unary minus For this special case JS CC features the amp directive The amp directive must be specified behind the rule s definition and in front of the semantic code action if there is any Behind the amp directive a terminal symbol both as string or its label is specified which precedence level is taken by the production instead of its default value So by changing the grammar to expr expr expr 2 1 33 expr expr 1 3 expr Vl expr a ee S SS expr expr 1 3 expr 35 22 expr amp 9 39 1 INT FLOAT we get the right parse tree and result because our rule with the unary minus has a higher precedence now and reduces instead of shifting in the desired cases JS CC User s Manual Page 17 of 34 4 Implementing a scripting language The idea As an example for a real mini compiler we will now implement a simple interpreted programming language called XPL eXample Programming Language using JS CC XPL is a C styled script language interpreter providing simple user input output operations
9. EOU le 25S VG Je Expression lt Expression 22 createNode NODE OPT OP LOT ales pees Expression gt Expression oo CreateNodel NODE OP OP GRT sl Se E Expression lt Expression to CreateNode NODE OP OP LOE AS Expression gt Expression createNode NODE OP OP GRE oll assy pee Expression Expression createNode NODE OP OP NEQ wll aS ee Expression 15 Expression oc CreateNode NODE OP OP SUB s os E Expression Expression Se ereateNode NODE OP OP ADD zi tas a Expression Expression createNode NODE OP OP MUL elle ash ete Expression Expression Se createNode NODE OP OP DIV oily ea ie y Expression gr createNode NODE OP OP NEG be i el U Expression 3 2 Integer tc Createnode NODE CONSTE ol J Float ts ereateNode NODE CONST lt l J Identifier ass createNode NODE VAR H Utility function Open and read a file function open file file var fs new ActiveXObject Scripting FileSystemObject var src new String if fs KK fs fileExists file var f fs OpenTextFile file 1 TEE JS CC User s Manual Page 27 of 34 src f ReadAll f Closel return src Main if WScript Arguments length gt 0 var str lopen fie Script Arguments ON var error cnt 107 var error off new Array var error la new Array if error cent _ PREFIX pars
10. T 456 INT FLOAT e gt gt a Shell Konsole LL AIC 7 E 2 A 15 34 Screenshot 2 The browser based JS CC web environment JS CC User s Manual Page 8 of 34 An example parser In parser generators like yacc a simple parser for mathematical expressions is the most widely used example to become familiar with the syntax and usage so we do this even here The parser definition language itself is described below in a more detailed way Store the following grammar definition into a text file of your choice For parser source files the PAR file extension could be used so the file is named calc par in such case This grammar will go with the platforms Rhino Spidermonkey and V8 To get it to work with JScript all input output operations need to be replaced by their particular WScript calls In Web Environment use JavaScript s common prompt and alert methods tt program expr term factor Expression calculator written in JS CC SV Tokens to be ignored e g whitespace comments of NM Grammar tokens UNE UNE ESO ypa TANG ND I I INT Smatch parselnt Smatch Ee 0 9 0 9 0 9 0 9 FLOAT Smatch parseFloat match The non terminal p is the entry symbol because it is the first one fi expr Dear SL El Don t confuse with the tokens Here we use the unescaped values because these are not interpretered as regular expressions at this p
11. above run JS CC like as follows rhino jscc js o calc js calc par That s all The result calc js can now simply be executed using your desired platform Shell Konsole Session Edit View Bookmarks Settings Help rhino jscc js o calc js calc par rhino calc js 3 4 5 Screenshot 3 Compiling and executing the calculator example As all nix like programs JS CC does output nothing when its invoked and successfully build the parser The verbose option prints out some statistics e g how many states and actions had been created in the resulting parse table JS CC User s Manual Page 11 of 34 3 The Grammar Definition Language General As you can get from the expression calculator example above the grammar definition language of JS CC consists of two parts The token definition part and the grammar part which defines the language s grammar using a Backus Naur Form styled meta language The two parts are separated by a symbol which could be seen as a Separating line between both parts Some things in the current version of the JS CC grammar definition language are a little bit nasty and need to be reworked in future like this separator The Terminal Declaration Part Tokens or terminal symbols are defined in the upper part of each grammar definition file These terminals are defined using a regular expression meta language but it s also possible to give each terminal symbol an individual name and a individua
12. ar variables and offsets later in the resulting parser The n wild cards are used to address every individual token starting from the left of the right hand side The wild card relates to the value of the left hand side which is pushed to the parser s value stack right after the right hand side symbols are popped So by passing a value to the wild card causes the inheritance of values from the current right hand side to another call of the according non terminal on a right hand side within the parse tree The values on the current right hand side will be discarded when the reduction process occurs and the value attached to is pushed instead so it can be used elsewhere JS CC User s Manual Page 15 of 34 As example in the given production expr expr term 3 1 43 of the above expression calculator the return values of the expr and the term on the right hand side which are addressed via 1 and 3 2 addresses the value of the terminal are added together and the result is stored to the left hand side the expr on the far left in this case Thus you have full control over all individual tokens within each production If no individual semantic action is given to a right hand side the default action 1 is used Semantic action between the symbols of a right hand side is not allowed only behind them Value types Because JS CC was designed for the use with JavaScipt or any other typeless scri
13. are Technologies Jan Max Meyer The complete source of this program is in the Public Domain This example demonstrates the implementation of XPL a complete interpretered scripting language written in JS CC XPL provides simple input output operations and can only handle numeric values Watch out for the xpl files within the example directory which contain example scripts to be executed using XPL LStruets function NODE var type var value var children Defines JS CC User s Manual Page 21 of 34 var NODE OP 0 var NODE VAR i var NODE CONST SP var OP NONE SL var OP ASSIGN 10 var OP_IF aly var OP_IF ELSE 2 var OP WHILE DO 3 var OP DO WHILE 4 var OP_WRITE 3 var OP_READ Gi var OP_SAY iF var OP_EQU 105 var OP_NEQ ally var OP_GRT 12 var OP_LOT ler var OP_GRE 14 var OP_LOE 157 var OP_ADD lr var OP SUB 175 var OP DIV Aeg var OP MUL SALE var OP NEG 207 Management functions function createNode type value childs var n new NODE n type type n value value n children new Array for var i 2 i lt arguments length i n children push arguments i return n Array to store variable names and values to var v_names new Array var v_values new Array Function to store a variable s content to a variables name If the name does not exist already the variable is automatically created
14. clamation mark symbol The whitespace symbols In this definition there is only one regular expression possible A label or code part is prohibited As whitespace tokens terminals that should always be ignored can be specified e g blanks tabs or comments JS CC User s Manual Page 14 of 34 The Grammar Definition Part The lower and most important part of a JS CC parser definition is the grammar definition part In this part below the symbol the definition of the context free grammar to be parsed by the generated parser is described This is done by using a Backus Naur Form variant meta language by defining non terminals and their productions The general syntax for a non terminal and its productions is non terminal production semantic code production semantic code production semantic code z The non terminal defines a single word identifier and acts as the left hand side for the related productions attached to this symbol The production defines a sequence of zero or multiple terminals and non terminals defining the different syntax rules To specify terminal symbols it is possible to call them via their unescaped regular expression as described above via a string value or by their label which must not but can be specified as a string value In the example of the quick start part both methods are used FLOAT is called by its label the token for better readability is called by it s generate
15. cript directly like in the first expression calculator example It probably works also here but only in expressions Statements like while do or if else are not directly interpretable because they have a body and a conditional part Because of that we need to compile the program internally into a structure for a virtual machine This virtual machine uses an assembly like command language working with opcodes and operands and running recursively on a tree structured compilation The parser has the purpose to build up a cascading structure of nodes which form the program that can be executed This method avoids the use of dealing with jumps to addresses but cannot be used to be written to a file Note that this compiler will not compile into an assembly code file The assembly program is constructed directly into the memory as an internal structure The virtual machine executing this structure will at least exist of one function which calls itself recursively based on the operation it executes The entire source This is the entire augmented program code for the XPL compiler and interpreter based on the grammar definition from above A script is executed from a file which must be attached to the script at startup Note that this code is for JScript to be executed using cscript To port it to another platform I O methods must be replaced or rewritten XPL eXample Programming Language v0 3 Written 2007 by J M K S F Softw
16. d and the complete chapter 6 Internal documentation has been removed The decision for removing this section is that JS CC s file structure has been completely changed and much more platforms came in Most of the internal documentation was only on describing the several source files of the package but this information is even hold in the source files itself So instead of revising this chapter it is now simply removed and the information necessary for hacking and building JS CC remains only in the sources Future plans Development on JS CC still moves on and the more people using it the more fun there is of developing it further Both the academic and productive ideas behind JS CC will be followed For future releases a more yacc styled behavior is planned plus some features taken from several other popular parser generator projects This includes virtual productions embedded semantics better analysis of the parse table generation process and much more An alternative JS CC front end with a lex yacc like syntax would complete the whole system It would be even possible to make JS CC a parser generator for other target platforms than ECMAScript but these are just ideas for now JS CC User s Manual Page 4 of 34 Some words by the author The kernel of JS CC is entirely written and maintained by me Jan Max Meyer I m a software developer and hobbyist programmer from Germany and was born in 1985 The art of compiler design i
17. d name which came from the regular expression The semantic code part behind the productions is optional and defines an individual semantic code which is executed right before the according production is reduced to its left hand side Same as in the token definition part semantic code is enclosed by and and will be concatenated to one code segment which is associated with the according productions when multiple semantic code segments are specified in a row Read more about this in the section below Note that in the above syntax scheme the number of productions is completely variable At least one right hand side must be given to an according left hand side although this can be an epsilon production Each production is separated by a vertical pipe bar from the others and a non terminal definition must always be closed by a semicolon Else JS CC can not distinguish if the next symbol belongs to the right hand side it currently parses or if it reads a new non terminal definition Non terminal symbols can be called on a right hand side before they are defined so the way the rules are defined is arbitrary Integrative checks on the grammar are done by JS CC before the parse tables will be constructed Accessing right hand side items in semantic action Within each semantic action attached to a production as described above the values of the right hand side symbols can be accessed via wild cards which are replaced by the particul
18. e str error off error la gt 0 for R i lt error vent itt WScript Echo Parse error near ste substi Gases ens H L LO ae ETT I T ar LO 8 Ge Fr WN expecting VF t error lagen FANG else WScript Echo usage xpl js lt filename gt JS CC User s Manual Page 28 of 34 5 Debugging parsers General When JS CC compiles a grammar the parse tables are inserted into a so called driver template which is then executing the state machine based on the content of the parse tables These parser drivers offer several methods to debug grammars depending on their platform JS CC comes with several parser driver templates for the different platforms it supports They are specified in the files driver_ lt platform gt js_ To build an executable parser JS CC uses one of these templates and copies the generated dynamically generated parse tables and arbitrary information into placeholders within the templates The result of this process is the executable parser script The grammar debugging features of the respective parse table driver are enabled by setting some global variables to true 58 p Screenshot 4 Console based parser debugging Parse trace and parse tree Shell Konsole Session Edit View Bookmarks Settings Source Stack 0 2 Value stack 0 58 Reducing by producution 1 Performing semantic action Popping 1 off the stack Pushing non terminal p Lookahead 42 Actio
19. executed in many different ways as platform independent browser based JavaScript embedded on a Website which comes with a graphical parse tree generator e asa Windows Script Host Application or a compiled JScript NET executable e asa Mozilla Rhino or Mozilla Spidermonkey interpreted application e oras a V8 shell script All versions can be build and run under Linux Windows Mac OSX and any other nix based operating system For productive execution it is recommended to use the command line versions which are capable of assembling a complete compiler from a JS CC parser specification which is then stored to a js JavaScript source file To use JS CC and for understanding its internals and behavior some knowledge of context free grammars bottom up parsing techniques and compiler construction theory in general is assumed To get a fundamental introduction to compiler design and the different techniques and appendages on this topic warmly suggest to the book Compiler Design in C written by Allen I Holub Maybe in future the JS CC user s manual itself or I ll write a system independent one will provide a detailed introduction on the very huge topic of compiler construction but for now limit this manual only on the usage of JS CC itself and its internals Enjoy I Allen I Holub Compiler Design in C Prentice Hall Software Series ISBN 978 0131550452 JS CC User s Manual Page 3 of 34 The intention behind JS CC
20. ghts against the senseless killing and capturing of marine animals like whales and dolphins which is unfortunately the case in some countries of the world today We must keep this world for us and our children and stop this senseless killing of endangered animals In my opinion every second counts To support the life of whales and dolphins in our oceans please visit http www wdcs org Thank you very much Whale and Dolphin Conservation Society JS CC User s Manual Page 5 of 34 2 A quick start example Building JS CC JS CC is a platform independent software Because of that you have to set it up for one platform By default JS CC is targeted to Mozilla Rhino when downloading the Tarball and to Jscript both Windows Script Host and NET when downloading the Windows setup Under Linux or your nix based system it is recommended to use GNU Make for all build operations under Windows Microsoft nmake is assumed Currently JS CC can be build for the following platforms and builds even parsers for those e Mozilla Rhino e Mozilla Spidermonkey e JScript Windows Script Host e JScript NET V8 Web environment HTML JavaScript entirely platform independent The Makefile for each supported platform can be found in the src directory and follows the naming convention Makefile lt platform gt To get additional help and how to on the various platforms and how to build JS CC there look into the Makefile header comments
21. haracter class is negated Character ranges can be specified using a dash For example A Za z specifies all capital and lower case alphabet letters Sub expression Or operator Allows to specify different expressions at one level dl Kleene closure operator none or many to be specified behind a character character class or sub expression Positive closure operator one or many to be specified behind a character character class or sub expression Optional closure operator one or none to be specified behind a character character class or sub expression Table 1 JS CC own regular expression meta language Even to allow case insensitive keywords within grammar definitions a terminal symbol definition can be specified using single quoted and double quoted strings A single quoted string means that a terminal symbol is matched case sensitive a double quoted one matches a terminal in any case order For example the terminal symbol definition PRINT will match for Print print PrINT and PRINT while the definition PRINT will only match for PRINT itself From these regular expression definitions JS CC constructs a deterministic finite automation which acts as lexer in the resulting parser Ambiguous Regular Expressions If there are ambiguous regular expressions where several expressions match the same string within the terminal definition part the expression
22. ing number it must be greater or equal 10 read count ist Counte lt 10 say y while count lt 10 say Starting sequence while count gt 0 do write count The number is lower 10 ignuation t 3 loops before Niift off if count say else if count 0 count count 1 Defining the grammar o ed say rand MIEC OEE The grammar definition for the XPL grammar consists of less than 80 lines of grammar definition l NINAS ot Ip ELSE WHILE po say WRITE READ pak icles z AZ IT A ISS EN OS Identifier String integer VO SON OS MOSSOS H E Float JS CC User s Manual Page 19 of 34 tt Program Stmt_List SEME Expression JS CC User s Manual IN tN yt V Expression Program Stmt Stmt_List Stmt F Expression Stmt IF Expression Stmt ELSE Stmt WHILE Expression DO Stmt DO Stmt WHILE Expression SAY String 17 WRITE Expression READ Identifier Identifier Expression senere mes Y 7 Expression Expression lt Expression Expression gt Expression Expression lt Expression Expression gt Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression GEN U Expression 1 Integer Float Identifier Page 20 of 34 Executing the script It is impossible to interpret an XPL s
23. l code segment to be executed when this token is recognized by the generated lexical analyzer e g to cut the leading and trailing quotation marks if a string is recognized from the token s attribute The general syntax to define tokens is regular expression label code where label and code is optional The regular expression is specified in the ways described below using a single or double quoted string A token s label is defined as a single word identifier e g FLOAT or INTEGER_NUMBER Not allowed are separated words If no label is specified JS CC uses the regular expression definition itself as label but without taking escape characters so the regular expression will result in the label as in the above example If itself is specified as regular expression a parse error will occur because the plus character is the symbol for a positive closure in regular expressions A semantic code action is defined by enclosing the desired JavaScript code segment with a and symbol If more than one code segment is specified in a row all segments are summarized to one segment to be attached to the terminal symbol To simply access things like the matched pattern the offset where the pattern starts or the source string in this individual code segments the wild cards Y match offset and source should be used These wild cards are later substituted by the particular variable names in the resulting lexical analyzer Beca
24. llowing the Copyright Holder to include your modifications in the Standard Version of the Package b use the modified Package only within your corporation or organization c rename any non standard executables so the names do not conflict with standard executables which must also be provided and provide a separate manual page for each non standard executable that clearly documents how it differs from the Standard Version d make other distribution arrangements with the Copyright Holder 4 You may distribute the programs of this Package in object code or executable form provided that you do at least ONE df the following a distribute a Standard Version of the executables and library files together with instructions in the manual page or equivalent on where to get the Standard Version b accompany the distribution with the machine readable source of the Package with your modifications c accompany any non standard executables with their corresponding Standard Version executables giving the non standard executables non standard names and clearly documenting the differences in manual pages or equivalent together with instructions on where to get the Standard Version d make other distribution arrangements with the Copyright Holder 5 You may charge a reasonable copying fee for any distribution of this Package You may charge any fee you choose for support of this Package You may not charge a fee for this Package itself Howeve
25. n O Source Stack 0 1 Value stack 0 Reducing by producution O Performing semantic action Popping 1 off the stack Parse complete Parse tree D G L Shell JS CC User s Manual Page 29 of 34 Debug facilities To enable the debugging facilities in console based parsers you can set the following variables depending on your requests Trace set PREFIX _dbg_withtrace to true The parse trace provides information about each parser state which is entered with which input tokens parse stack and value stack This feature is very useful to understand the parse process and to detect possible value access errors Step by step set PREFIX _dbg_withstepbystep to true This can only be used in conjunction with the parse trace and waits that the user presses enter to continue to the next state Has no effect when trace is switched off Parse tree generation set PREFIX _dbg_withparsetree to true Generates a parse tree at the end of the parse This parse tree which is printed in a pseudo graphical tree view represents the structure of the complete parsed input splitted into all the used productions and tokens at the leafes of the tree To switch the debugging facilities on set the variables in the brackets above to true before invoking the parser entry function The PREFIX will be replaced by the optionally defined prefix you set when calling JS CC The following table gives a
26. ng about copying or distributing this Package e Reasonable copying fee is whatever you can justify on the basis of media cost duplication charges time of people involved and so on You will not be required to justify it to the Copyright Holder but only to the computing community at large as a market that must bear the fee e Freely Available means that no fee is charged for the item itself though there may be fees involved in handling the item It also means that recipients of the item may redistribute it under the same conditions they received it 1 You may make and give away verbatim copies of the source form of the Standard Version of this Package without restriction provided that you duplicate all of the original copyright notices and associated disclaimers 2 You may apply bug fixes portability fixes and other modifications derived from the Public Domain or from the Copyright Holder A Package modified in such a way shall still be considered the Standard Version 3 You may otherwise modify your copy of this Package in any way provided that you insert a prominent notice in each changed file stating how and when you changed that file and provided that you do at least ONE of the following a place your modifications in the Public Domain or otherwise make them Freely Available such as by posting said modifications to Usenet or an equivalent medium or placing the modifications on a major archive site such as ftp uu net or by a
27. o execute node children 0 break case OP_READ letvar node children 0 toString break case OP SAY WScript StdIn ReadLine WScript Echo node children 0 break case OP EQU E break case OP NEQ Bees break case OP GRT ret s break case OP_LOT ret break case OP GRE ret break case OP_LOE ret break case OP_ADD execute node children 0 execute node children 1 execute node children 0 execute node children 1 execute node children 0 gt execute node children 1 execute node children 0 lt execute node children 1 execute node children 0 gt execute node children 1 execute node children 0 lt execute node children 1 Page 24 of 34 ret execute node children 0 execute node children 1 break case OP_SUB ret execute node children 0 execute node children 1 break case OP DIV ret execute node children 0 execute node children 1 break case OP MUL ret execute node children 0 execute node children 1 break case OP NEG ret execute node children 0 1 break break case NODE VAR ret Number getvar node value break case NODE CONST ret Number node value break return ret a Defining whitespaces and comments AAA Keywords
28. osition otf expr term 83 S31 63 expr term SS SL 3 term Default semantic action fits here term factor SG SL 37 term os 3 1 3 ale tox Default semantic action fits here TT expr Ty 33 2 INT Default semantic action fits here FLOAT Default semantic action fits here 7 This is the parser entry point JS CC User s Manual Because this entry point could be very individual Page 9 of 34 the compiler programmer has to decide which way he wants to read the source parse it and report the errors if there are any var error offsets new Array var error lookaheads new Array var error count 0 We re getting the expression via command line parameter g g var str new String arguments 0 The PREFIX is a wild card where an optional SI unique name will be inserted by JS CC when the parser is constructed This enables the possibility to use multiple different parsers in one project or script KZ if error count __ PREFIX parse str error Onisets error loo kate sadsi 0 for i 0 i lt error count itt print Parse error near Sta sul sien eramos ets anim YA expecting V error llookaheads 1 Join Di JS CC User s Manual nn au Page 10 of 34 Compiling the example To compile a working parser from the example described
29. owser based JavaScript ECMAScript applications WARNING This parser template will not run as console and has lesser features for debugging than the console derivates for the various JavaScript platforms Features Parser trace messages Integrated panic mode error recovery Written 2007 2008 by Jan Max Meyer J M K S F Software Technologies This is in the public domain var _dbg_withtrace false var _dbg_string new String Screenshot 5 Graphical parse tree feature in Web Environment JS CC User s Manual Page 31 of 34 License Agreements JS CC is released under the Artistic License Preamble The intent of this document is to state the conditions under which a Package may be copied such that the Copyright Holder maintains some semblance of artistic control over the development of the package while giving the users of the package the right to use and distribute the Package in a more or less customary fashion plus the right to make reasonable modifications Definitions e Package refers to the collection of files distributed by the Copyright Holder and derivatives of that collection of files created through textual modification ka Standard Version refers to such a Package if it has not been modified or has been modified in accordance with the wishes of the Copyright Holder Copyright Holder is whoever is named in the copyright or copyrights for the package e You is you if you re thinki
30. pting language it is not necessary to define as in yacc a special union structure to hold the values on the value stack Both build in primary types like String or Number objects as well as user defined objects each function in JavaScript is internally represented by an object can be pushed to and popped off the value stack So don t confuse with the values You have to know which objects you push on the stack Resolving conflicts To automatically resolve shift reduce or reduce reduce conflicts at parse table generation JS CC features by default two mechanisms When a shift reduce conflict occurs JS CC constructs the parse tables in favor of the shift so the parse tree will grow right derivative When a reduce reduce conflict occurs JS CC resolves the problem by reducing the production which was defined first so productions which where defined above in the grammar will be reduced in favor when this conflict comes up As shortly described in the chapter about terminal symbol definition JS CC features the possibility of manipulating the natural parse table generated by the LALR 1 table construction algorithm by weighting terminal symbols with a precedence level and an associativity This information is used within shift reduce conflicts to better decide if a shift or a reduce operation should be inserted If a shift reduce conflict comes up the precedence level and associativity information is compared with the according prod
31. r you may distribute this Package in aggregate with other possibly commercial programs as part of a larger possibly commercial software distribution provided that you do not advertise this Package as a product of your own 6 The scripts and library files supplied as input to or produced as output from the programs of this Package do not automatically fall under the copyright of this Package but belong to whomever generated them and may be sold commercially and may be aggregated with this Package JS CC User s Manual Page 32 of 34 7 Subroutines supplied by you and linked into this Package shall not be considered part of this Package 8 The name of the Copyright Holder may not be used to endorse or promote products derived from this software without specific prior written permission 9 THIS PACKAGE IS PROVIDED AS IS AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES INCLUDING WITHOUT LIMITATION THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FORA PARTICULAR PURPOSE JS CC User s Manual Page 33 of 34 Credits Thanks a lot to Louis P Santillan for his efforts in porting JS CC to several platforms and for his help on the project A salute to all that real coders in the world from Jan Max and Fynn JS CC User s Manual Page 34 of 34
32. s a study on my own because it very much interests me and makes a lot of fun This project is one result of this study never studied on computer sciences yet but plan this somewhere in the future In my professional life work as application software developer at a local business software company As one of my hobbies I also run my own tiny software company this is J M K S F Software Technologies from home where I m in writing programs and solutions around the area of software development tools application software and some web solutions JS CC is a non profit based product of this business There is also another project in the area of computer aided recognizer generation where I m currently on but more about this will be found out when its finished and if really release it Now wish you much fun and success on using JS CC hope that this software will be useful in your business or just helps you on understanding how bottom up parsing works a little more clearly would deeply appreciate if you have the fun and engagement on developing JS CC further Share it with others make it popular or hack its code That s the way it is meant to be So long Jan PS If you really like JS CC and if you want to give me a smart pleasure for my efforts in developing this software would be very happy if you maybe take a huger or lesser donation to the WDCS Whale and Dolphin Conservation Society an organization that fi
33. s defined upper in the terminal definition part will take higher match precedence than the lower defined terminals It is recommended to define tokens with a higher specialization level as the first and tokens with a lower level as the last in JS CC User s Manual Page 13 of 34 your token definition part Associativity and Precedence Tokens can be grouped by precedence levels and associativity This features allows to write faster and even smaller grammars by resolving grammar conflicts by weighting terminal symbols A group without a group specifier will set no associativity and a precedence level of zero to all terminal symbols in this group as in the first example Else if a group begins with the symbol lt for left associativity gt for right associativity and for non associativity all terminal symbols within this group are set to the according associativity and precedence level The precedence level is incremented each time a new group of these three types is opened so groups that are defined at the bottom of the token definition part take the highest precedence The precedence information as associativity is used to resolve conflicts in ambiguous grammars by modifying the parse table s natural content How this works in practice and what ways and possibilities there are is described below in the section dialing with grammar conflicts and their handling Whitespace A special type of terminal symbol is introduced by the ex
34. sage jscc options filename help Print this usage help version Print version and copyright output lt file gt Save output source to lt file gt prefix lt prefix gt Use lt prefix gt as sequence pre fixing methods and variables template lt file gt Use template file lt file gt as parser template verbose Run in verbose mode warnings Print warnings Screenshot 1 Building and invoking JS CC from a shell To run JS CC with Rhino do rhino jscc js and smjs jscc js for the Spidermonkey version or simply jscc js when execute permission is set v8sh jscc js will run the V8 engine as platform JS CC User s Manual Page 7 of 34 To complete the list of invoking commands run webenv jscc html with your favorite JavaScript enabled browser for the web environment JS CC Web Environment Mozilla Firefox 9 file home neo jsccwebenvijscc htm C Google 9 file bi html IG E JV Web Environment Version 0 29 Copyright 2007 2008 by Jan Max Meyer J M K S F Software Technologies http jsee jmksf com ditor rammar Characters to be ignored INE Non associative tokens AC a show warnings Grammar State Overview amp Parse Tables rammar Overview Left hand side FIRST set Right hand side INT FLOAT p e e e ff e 579 M e 123 e e INT FLOAT oi R maz Aol s 41 e Ae i e aso FLOAT GR IN
35. short overview about each template and the supported debug features Driver File Platform Trace StepByStep ParseTree driver_rhino js_ Mozilla Rhino X X X driver_sm js_ Mozilla Spidermonkey X X driver_jscript js_ Microsoft JScript WSH X X X Microsoft JScript NET driver_v8 js_ Google V8 X X X driver_web js_ Platform independent X JavaScript driver_webenv js_ Platform independent X JavaScript for the JS CC Web Environment always JS CC User s Manual Table 2 Default parser drivers Page 30 of 34 Debugging with the Web Environment When using the Web Environment JS CC automatically provides a parser that constructs a visual parse tree out of the parser s input This parse tree looks much nicer than the pseudo graphical one that is printed on the console The Web Environment uses a modified version of the web driver so debug must not be explicitly be enabled it is always turned on JS CC Web Environment Mozilla Firefox a ia file home neo jscc webenv jscc html IG Show warnings Grammar state Overview Parse Tables C rammar Overview Q e 23 Left hand side FIRST set Right hand side kad e 3 pr INT FLOAT p l daze R m e e A ere INT FLOAT sees e e 6 ala kad e 4 ve Sy m a E e FLOAT A p INT FLOAT e e s Parser Source Code O Default template driver for JS CC generated parsers running as br
36. uction s precedence level because every production will by default get the same precedence level as its rightmost terminal symbol To explain this behavior let s look at the following example It defines a calculator same as the first example but with lesser effort in writing the grammar Here we have only two non terminal symbols instead of four but we implement the same operator precedence behavior as in the original one Tokens to be ignored e g whitespace comments 1 N Left associative tokens lowest precedence f F UE Not Left associative tokens highest precedence ee EG UN JS CC User s Manual Page 16 of 34 E Tokens with no associativity VANG ENJ OSONT INT Smatch parselnt Smatch sa 0 9 0 9 0 9 0 9 FLOAT Smatch parseFloat match fi program expr print SL LAT expr expr expr 26 SL 33 expr expr SS SL e expr expr LS 23 31 337 expr expr 3 1 3 Et expr 8 2 INT FLOAT Sometimes it will also be necessary to give a production another precedence level than the one of the rightmost terminal For example if we want to add an unary minus operator to the grammar above the production adopts the precedence level of the minus symbol by default But this minus operator was configured for its use in a binary subtraction not in an unary subtraction By simply adding a new rule for unary minus
37. use JS CC does also allow to pass precedence and associativity information to tokens or token groups each block of token definitions is closed by a semicolon Because of that the semicolon is set behind the last token definition also in the above example even if we don t use any precedence information here Regular Expressions Because it was impossible to build a properly working lexical analyzer using JavaScript s build in RegExp object JS CC features its own implementation of regular expression processing This is also the reason that not all the features of the JavaScript RegExp object are provided like back references and predefined character classes JS CC User s Manual Page 12 of 34 The symbols and operators to be used within JS CC s own regular expression language are summarized in the following table They form a minimal implementation of a regular expression engine Language Element Description character One character specifies exactly that character If a regular expression operator like or should be used it must be escaped via ascii code One character defined via ASCII code e g 220 matches the U umlaut of the extended ASCII table character Escaped character Must be used when a character of the meta language itself should be matched e g V Any character character class matching all available characters L Character class If a beginning circumflex is given the c
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