'\" '\" Generated from file 'me_vm\&.man' by tcllib/doctools with format 'nroff' '\" Copyright (c) 2005 Andreas Kupries '\" .TH "grammar::me_vm" 3tcl 0\&.1 tcllib "Grammar operations and usage" .\" The -*- nroff -*- definitions below are for supplemental macros used .\" in Tcl/Tk manual entries. .\" .\" .AP type name in/out ?indent? .\" Start paragraph describing an argument to a library procedure. .\" type is type of argument (int, etc.), in/out is either "in", "out", .\" or "in/out" to describe whether procedure reads or modifies arg, .\" and indent is equivalent to second arg of .IP (shouldn't ever be .\" needed; use .AS below instead) .\" .\" .AS ?type? ?name? .\" Give maximum sizes of arguments for setting tab stops. Type and .\" name are examples of largest possible arguments that will be passed .\" to .AP later. If args are omitted, default tab stops are used. .\" .\" .BS .\" Start box enclosure. From here until next .BE, everything will be .\" enclosed in one large box. .\" .\" .BE .\" End of box enclosure. .\" .\" .CS .\" Begin code excerpt. .\" .\" .CE .\" End code excerpt. .\" .\" .VS ?version? ?br? .\" Begin vertical sidebar, for use in marking newly-changed parts .\" of man pages. The first argument is ignored and used for recording .\" the version when the .VS was added, so that the sidebars can be .\" found and removed when they reach a certain age. If another argument .\" is present, then a line break is forced before starting the sidebar. .\" .\" .VE .\" End of vertical sidebar. .\" .\" .DS .\" Begin an indented unfilled display. .\" .\" .DE .\" End of indented unfilled display. .\" .\" .SO ?manpage? .\" Start of list of standard options for a Tk widget. The manpage .\" argument defines where to look up the standard options; if .\" omitted, defaults to "options". The options follow on successive .\" lines, in three columns separated by tabs. .\" .\" .SE .\" End of list of standard options for a Tk widget. .\" .\" .OP cmdName dbName dbClass .\" Start of description of a specific option. cmdName gives the .\" option's name as specified in the class command, dbName gives .\" the option's name in the option database, and dbClass gives .\" the option's class in the option database. .\" .\" .UL arg1 arg2 .\" Print arg1 underlined, then print arg2 normally. .\" .\" .QW arg1 ?arg2? .\" Print arg1 in quotes, then arg2 normally (for trailing punctuation). .\" .\" .PQ arg1 ?arg2? .\" Print an open parenthesis, arg1 in quotes, then arg2 normally .\" (for trailing punctuation) and then a closing parenthesis. .\" .\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. .if t .wh -1.3i ^B .nr ^l \n(.l .ad b .\" # Start an argument description .de AP .ie !"\\$4"" .TP \\$4 .el \{\ . ie !"\\$2"" .TP \\n()Cu . el .TP 15 .\} .ta \\n()Au \\n()Bu .ie !"\\$3"" \{\ \&\\$1 \\fI\\$2\\fP (\\$3) .\".b .\} .el \{\ .br .ie !"\\$2"" \{\ \&\\$1 \\fI\\$2\\fP .\} .el \{\ \&\\fI\\$1\\fP .\} .\} .. .\" # define tabbing values for .AP .de AS .nr )A 10n .if !"\\$1"" .nr )A \\w'\\$1'u+3n .nr )B \\n()Au+15n .\" .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n .nr )C \\n()Bu+\\w'(in/out)'u+2n .. .AS Tcl_Interp Tcl_CreateInterp in/out .\" # BS - start boxed text .\" # ^y = starting y location .\" # ^b = 1 .de BS .br .mk ^y .nr ^b 1u .if n .nf .if n .ti 0 .if n \l'\\n(.lu\(ul' .if n .fi .. .\" # BE - end boxed text (draw box now) .de BE .nf .ti 0 .mk ^t .ie n \l'\\n(^lu\(ul' .el \{\ .\" Draw four-sided box normally, but don't draw top of .\" box if the box started on an earlier page. .ie !\\n(^b-1 \{\ \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .el \}\ \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' .\} .\} .fi .br .nr ^b 0 .. .\" # VS - start vertical sidebar .\" # ^Y = starting y location .\" # ^v = 1 (for troff; for nroff this doesn't matter) .de VS .if !"\\$2"" .br .mk ^Y .ie n 'mc \s12\(br\s0 .el .nr ^v 1u .. .\" # VE - end of vertical sidebar .de VE .ie n 'mc .el \{\ .ev 2 .nf .ti 0 .mk ^t \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' .sp -1 .fi .ev .\} .nr ^v 0 .. .\" # Special macro to handle page bottom: finish off current .\" # box/sidebar if in box/sidebar mode, then invoked standard .\" # page bottom macro. .de ^B .ev 2 'ti 0 'nf .mk ^t .if \\n(^b \{\ .\" Draw three-sided box if this is the box's first page, .\" draw two sides but no top otherwise. .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c .\} .if \\n(^v \{\ .nr ^x \\n(^tu+1v-\\n(^Yu \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c .\} .bp 'fi .ev .if \\n(^b \{\ .mk ^y .nr ^b 2 .\} .if \\n(^v \{\ .mk ^Y .\} .. .\" # DS - begin display .de DS .RS .nf .sp .. .\" # DE - end display .de DE .fi .RE .sp .. .\" # SO - start of list of standard options .de SO 'ie '\\$1'' .ds So \\fBoptions\\fR 'el .ds So \\fB\\$1\\fR .SH "STANDARD OPTIONS" .LP .nf .ta 5.5c 11c .ft B .. .\" # SE - end of list of standard options .de SE .fi .ft R .LP See the \\*(So manual entry for details on the standard options. .. .\" # OP - start of full description for a single option .de OP .LP .nf .ta 4c Command-Line Name: \\fB\\$1\\fR Database Name: \\fB\\$2\\fR Database Class: \\fB\\$3\\fR .fi .IP .. .\" # CS - begin code excerpt .de CS .RS .nf .ta .25i .5i .75i 1i .. .\" # CE - end code excerpt .de CE .fi .RE .. .\" # UL - underline word .de UL \\$1\l'|0\(ul'\\$2 .. .\" # QW - apply quotation marks to word .de QW .ie '\\*(lq'"' ``\\$1''\\$2 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\$2 .. .\" # PQ - apply parens and quotation marks to word .de PQ .ie '\\*(lq'"' (``\\$1''\\$2)\\$3 .\"" fix emacs highlighting .el (\\*(lq\\$1\\*(rq\\$2)\\$3 .. .\" # QR - quoted range .de QR .ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3 .\"" fix emacs highlighting .el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3 .. .\" # MT - "empty" string .de MT .QW "" .. .BS .SH NAME grammar::me_vm \- Virtual machine for parsing token streams .SH DESCRIPTION Please go and read the document \fBgrammar::me_intro\fR first for an overview of the various documents and their relations\&. .PP This document specifies a virtual machine for the controlled matching and parsing of token streams, creating an \fIabstract syntax tree\fR (short \fIAST\fR) reflecting the structure of the input\&. Special machine features are the caching and reuse of partial results, caching of the encountered input, and the ability to backtrack in both input and AST creation\&. .PP These features make the specified virtual machine especially useful to packrat parsers based on parsing expression grammars\&. It is however not restricted to this type of parser\&. Normal LL and LR parsers can be implemented with it as well\&. .PP The following sections will discuss first the abstract state kept by ME virtual machines, and then their instruction set\&. .SH "MACHINE STATE" A ME virtual machine manages the following state: .TP \fICurrent token\fR CT The token from the input under consideration by the machine\&. .sp This information is used and modified by the instructions defined in the section \fBTERMINAL MATCHING\fR\&. .TP \fICurrent location\fR CL The location of the \fIcurrent token\fR in the input stream, as offset relative to the beginning of the stream\&. The first token is considered to be at offset \fB0\fR\&. .sp This information is implicitly used and modified by the instructions defined in the sections \fBTERMINAL MATCHING\fR and \fBNONTERMINAL MATCHING\fR, and can be directly queried and modified by the instructions defined in section \fBINPUT LOCATION HANDLING\fR\&. .TP \fILocation stack\fR LS In addition to the above a stack of locations, for backtracking\&. Locations can put on the stack, removed from it, and removed with setting the current location\&. .sp This information is implicitly used and modified by the instructions defined in the sections \fBTERMINAL MATCHING\fR and \fBNONTERMINAL MATCHING\fR, and can be directly queried and modified by the instructions defined in section \fBINPUT LOCATION HANDLING\fR\&. .TP \fIMatch status\fR OK A boolean value, the result of the last attempt at matching input\&. It is set to \fBtrue\fR if that attempt was successful, and \fBfalse\fR otherwise\&. .sp This information is influenced by the instructions defined in the sections \fBTERMINAL MATCHING\fR, \fBNONTERMINAL MATCHING\fR, and \fBUNCONDITIONAL MATCHING\fR\&. It is queried by the instructions defined in the section \fBCONTROL FLOW\fR\&. .TP \fISemantic value\fR SV The semantic value associated with (generated by) the last attempt at matching input\&. Contains either the empty string or a node for the abstract syntax tree constructed from the input\&. .sp This information is influenced by the instructions defined in the sections \fBSEMANTIC VALUES\fR, and \fBAST STACK HANDLING\fR\&. .TP \fIAST stack\fR AS A stack of partial abstract syntax trees constructed by the machine during matching\&. .sp This information is influenced by the instructions defined in the sections \fBSEMANTIC VALUES\fR, and \fBAST STACK HANDLING\fR\&. .TP \fIAST Marker stack\fR MS In addition to the above a stack of stacks, for backtracking\&. This is actually a stack of markers into the AST stack, thus implicitly snapshooting the state of the AST stack at some point in time\&. Markers can be put on the stack, dropped from it, and used to roll back the AST stack to an earlier state\&. .sp This information is influenced by the instructions defined in the sections \fBSEMANTIC VALUES\fR, and \fBAST STACK HANDLING\fR\&. .TP \fIError status\fR ER Error information associated with the last attempt at matching input\&. Contains either the empty string or a list of 2 elements, a location in the input and a list of error messages associated with it, in this order\&. .sp \fINote\fR that error information can be set even if the last attempt at matching input was successful\&. For example the *-operator (matching a sub-expression zero or more times) in a parsing expression grammar is always successful, even if it encounters a problem further in the input and has to backtrack\&. Such problems must not be forgotten when continuing to match\&. .sp This information is queried and influenced by the instructions defined in the sections \fBTERMINAL MATCHING\fR, \fBNONTERMINAL MATCHING\fR, and \fBERROR HANDLING\fR\&. .TP \fIError stack\fR ES In addition to the above a stack of error information, to allow the merging of current and older error information when performing backtracking in choices after an unsucessful match\&. .sp This information is queried and influenced by the instructions defined in the sections \fBTERMINAL MATCHING\fR, \fBNONTERMINAL MATCHING\fR, and \fBERROR HANDLING\fR\&. .TP \fIReturn stack\fR RS A stack of program counter values, i\&.e\&. locations in the code controlling the virtual machine, for the management of subroutine calls, i\&.e\&. the matching of nonterminal symbols\&. .sp This information is queried and influenced by the instructions defined in the section \fBNONTERMINAL MATCHING\fR\&. .TP \fINonterminal cache\fR NC A cache of machine states (A 4-tuple containing a location in the input, match status \fIOK\fR, semantic value \fISV\fR, and error status \fIER\fR) keyed by name of nonterminal symbol and location in the input stream\&. .sp The key location is where machine started the attempt to match the named nonterminal symbol, and the location in the value is where machine ended up after the attempt completed, independent of the success of the attempt\&. .sp This status is queried and influenced by the instructions defined in the section \fBNONTERMINAL MATCHING\fR\&. .PP .SH "MACHINE INSTRUCTIONS" With the machine state specified it is now possible to explain the instruction set of ME virtual machines\&. They are grouped roughly by the machine state they influence and/or query\&. .SS "TERMINAL MATCHING" First the instructions to match tokens from the input stream, and by extension all terminal symbols\&. .PP These instructions are the only ones which may retrieve a new token from the input stream\&. This is a \fImay\fR and not a \fIwill\fR because the instructions will a retrieve new token if, and only if the current location \fICL\fR is at the head of the stream\&. If the machine has backtracked (see \fBicl_rewind\fR) the instructions will retrieve the token to compare against from the internal cache\&. .PP .TP \fBict_advance\fR \fImessage\fR This instruction tries to advance to the next token in the input stream, i\&.e\&. the one after the current location \fICL\fR\&. The instruction will fail if, and only if the end of the input stream is reached, i\&.e\&. if there is no next token\&. .sp The sucess/failure of the instruction is remembered in the match status \fIOK\fR\&. In the case of failure the error status \fIER\fR is set to the current location and the message \fImessage\fR\&. In the case of success the error status \fIER\fR is cleared, the new token is made the current token \fICT\fR, and the new location is made the current location \fICL\fR\&. .sp The argument \fImessage\fR is a reference to the string to put into the error status \fIER\fR, if such is needed\&. .TP \fBict_match_token\fR \fItok\fR \fImessage\fR This instruction tests the current token \fICT\fR for equality with the argument \fItok\fR and records the result in the match status \fIOK\fR\&. The instruction fails if the current token is not equal to \fItok\fR\&. .sp In case of failure the error status \fIER\fR is set to the current location \fICL\fR and the message \fImessage\fR, and the current location \fICL\fR is moved one token backwards\&. Otherwise, i\&.e\&. upon success, the error status \fIER\fR is cleared and the current location \fICL\fR is not touched\&. .TP \fBict_match_tokrange\fR \fItokbegin\fR \fItokend\fR \fImessage\fR This instruction tests the current token \fICT\fR for being in the range of tokens from \fItokbegin\fR to \fItokend\fR (inclusive) and records the result in the match status \fIOK\fR\&. The instruction fails if the current token is not inside the range\&. .sp In case of failure the error status \fIER\fR is set to the current location \fICL\fR and the message \fImessage\fR, and the current location \fICL\fR is moved one token backwards\&. Otherwise, i\&.e\&. upon success, the error status \fIER\fR is cleared and the current location \fICL\fR is not touched\&. .TP \fBict_match_tokclass\fR \fIcode\fR \fImessage\fR This instruction tests the current token \fICT\fR for being a member of the token class \fIcode\fR and records the result in the match status \fIOK\fR\&. The instruction fails if the current token is not a member of the specified class\&. .sp In case of failure the error status \fIER\fR is set to the current location \fICL\fR and the message \fImessage\fR, and the current location \fICL\fR is moved one token backwards\&. Otherwise, i\&.e\&. upon success, the error status \fIER\fR is cleared and the current location \fICL\fR is not touched\&. .sp Currently the following classes are legal: .RS .TP alnum A token is accepted if it is a unicode alphabetical character, or a digit\&. .TP alpha A token is accepted if it is a unicode alphabetical character\&. .TP digit A token is accepted if it is a unicode digit character\&. .TP xdigit A token is accepted if it is a hexadecimal digit character\&. .TP punct A token is accepted if it is a unicode punctuation character\&. .TP space A token is accepted if it is a unicode space character\&. .RE .PP .PP .SS "NONTERMINAL MATCHING" The instructions in this section handle the matching of nonterminal symbols\&. They query the nonterminal cache \fINC\fR for saved information, and put such information into the cache\&. .PP The usage of the cache is a performance aid for backtracking parsers, allowing them to avoid an expensive rematch of complex nonterminal symbols if they have been encountered before\&. .PP .TP \fBinc_restore\fR \fIbranchlabel\fR \fInt\fR This instruction checks if the nonterminal cache \fINC\fR contains information about the nonterminal symbol \fInt\fR, at the current location \fICL\fR\&. If that is the case the instruction will update the machine state (current location \fICL\fR, match status \fIOK\fR, semantic value \fISV\fR, and error status \fIER\fR) with the found information and continue execution at the instruction refered to by the \fIbranchlabel\fR\&. The new current location \fICL\fR will be the last token matched by the nonterminal symbol, i\&.e\&. belonging to it\&. .sp If no information was found the instruction will continue execution at the next instruction\&. .sp Together with \fBicf_ntcall\fR it is possible to generate code for memoized and non-memoized matching of nonterminal symbols, either as subroutine calls, or inlined in the caller\&. .TP \fBinc_save\fR \fInt\fR This instruction saves the current state of the machine (current location \fICL\fR, match status \fIOK\fR, semantic value \fISV\fR, and error status \fIER\fR), to the nonterminal cache \fINC\fR\&. It will also pop an entry from the location stack \fILS\fR and save it as the start location of the match\&. .sp It is expected to be called at the end of matching a nonterminal symbol, with \fInt\fR the name of the nonterminal symbol the code was working on\&. This allows the instruction \fBinc_restore\fR to check for and retrieve the data, should we have to match this nonterminal symbol at the same location again, during backtracking\&. .TP \fBicf_ntcall\fR \fIbranchlabel\fR This instruction invokes the code for matching the nonterminal symbol \fInt\fR as a subroutine\&. To this end it stores the current program counter \fIPC\fR on the return stack \fIRS\fR, the current location \fICL\fR on the location stack \fILS\fR, and then continues execution at the address \fIbranchlabel\fR\&. .sp The next matching \fBicf_ntreturn\fR will cause the execution to continue at the instruction coming after the call\&. .TP \fBicf_ntreturn\fR This instruction will pop an entry from the return stack \fIRS\fR, assign it to the program counter \fIPC\fR, and then continue execution at the new address\&. .PP .PP .SS "UNCONDITIONAL MATCHING" The instructions in this section are the remaining match operators\&. They change the match status \fIOK\fR directly and unconditionally\&. .TP \fBiok_ok\fR This instruction sets the match status \fIOK\fR to \fBtrue\fR, indicating a successful match\&. .TP \fBiok_fail\fR This instruction sets the match status \fIOK\fR to \fBfalse\fR, indicating a failed match\&. .TP \fBiok_negate\fR This instruction negates the match status \fIOK\fR, turning a failure into a success and vice versa\&. .PP .PP .SS "CONTROL FLOW" The instructions in this section implement both conditional and unconditional control flow\&. The conditional jumps query the match status \fIOK\fR\&. .TP \fBicf_jalways\fR \fIbranchlabel\fR This instruction sets the program counter \fIPC\fR to the address specified by \fIbranchlabel\fR and then continues execution from there\&. This is an unconditional jump\&. .TP \fBicf_jok\fR \fIbranchlabel\fR This instruction sets the program counter \fIPC\fR to the address specified by \fIbranchlabel\fR\&. This happens if, and only if the match status \fIOK\fR indicates a success\&. Otherwise it simply continues execution at the next instruction\&. This is a conditional jump\&. .TP \fBicf_jfail\fR \fIbranchlabel\fR This instruction sets the program counter \fIPC\fR to the address specified by \fIbranchlabel\fR\&. This happens if, and only if the match status \fIOK\fR indicates a failure\&. Otherwise it simply continues execution at the next instruction\&. This is a conditional jump\&. .TP \fBicf_halt\fR This instruction halts the machine and blocks any further execution\&. .PP .SS "INPUT LOCATION HANDLING" The instructions in this section are for backtracking, they manipulate the current location \fICL\fR of the machine state\&. They allow a user of the machine to query and save locations in the input, and to rewind the current location \fICL\fR to saved locations, making them one of the components enabling the implementation of backtracking parsers\&. .TP \fBicl_push\fR This instruction pushes a copy of the current location \fICL\fR on the location stack \fILS\fR\&. .TP \fBicl_rewind\fR This instruction pops an entry from the location stack \fILS\fR and then moves the current location \fICL\fR back to this point in the input\&. .TP \fBicl_pop\fR This instruction pops an entry from the location stack \fILS\fR and discards it\&. .PP .PP .SS "ERROR HANDLING" The instructions in this section provide read and write access to the error status \fIER\fR of the machine\&. .TP \fBier_push\fR This instruction pushes a copy of the current error status \fIER\fR on the error stack \fIES\fR\&. .TP \fBier_clear\fR This instruction clears the error status \fIER\fR\&. .TP \fBier_nonterminal\fR \fImessage\fR This instruction checks if the error status \fIER\fR contains an error whose location is just past the location found in the top entry of the location stack \fILS\fR\&. Nothing happens if no such error is found\&. Otherwise the found error is replaced by an error at the location found on the stack, having the message \fImessage\fR\&. .TP \fBier_merge\fR This instruction pops an entry from the error stack \fIES\fR, merges it with the current error status \fIER\fR and stores the result of the merge as the new error status \fIER\fR\&. .sp The merge is performed as described below: .sp If one of the two error states is empty the other is chosen\&. If neither error state is empty, and refering to different locations, then the error state with the location further in the input is chosen\&. If both error states refer to the same location their messages are merged (with removing duplicates)\&. .PP .SS "SEMANTIC VALUES" The instructions in this section manipulate the semantic value \fISV\fR\&. .TP \fBisv_clear\fR This instruction clears the semantic value \fISV\fR\&. .TP \fBisv_terminal\fR This instruction creates a terminal AST node for the current token \fICT\fR, makes it the semantic value \fISV\fR, and also pushes the node on the AST stack \fIAS\fR\&. .TP \fBisv_nonterminal_leaf\fR \fInt\fR This instruction creates a nonterminal AST node without any children for the nonterminal \fInt\fR, and makes it the semantic value \fISV\fR\&. .sp This instruction should be executed if, and only if the match status \fIOK\fR indicates a success\&. In the case of a failure \fBisv_clear\fR should be called\&. .TP \fBisv_nonterminal_range\fR \fInt\fR This instruction creates a nonterminal AST node for the nonterminal \fInt\fR, with a single terminal node as its child, and makes this AST the semantic value \fISV\fR\&. The terminal node refers to the input string from the location found on top of the location stack \fILS\fR to the current location \fICL\fR (both inclusive)\&. .sp This instruction should be executed if, and only if the match status \fIOK\fR indicates a success\&. In the case of a failure \fBisv_clear\fR should be called\&. .TP \fBisv_nonterminal_reduce\fR \fInt\fR This instruction creates a nonterminal AST node for the nonterminal \fInt\fR and makes it the semantic value \fISV\fR\&. .sp All entries on the AST stack \fIAS\fR above the marker found in the top entry of the AST Marker stack \fIMS\fR become children of the new node, with the entry at the stack top becoming the rightmost child\&. If the AST Marker stack \fIMS\fR is empty the whole stack is used\&. The AST marker stack \fIMS\fR is left unchanged\&. .sp This instruction should be executed if, and only if the match status \fIOK\fR indicates a success\&. In the case of a failure \fBisv_clear\fR should be called\&. .PP .PP .SS "AST STACK HANDLING" The instructions in this section manipulate the AST stack \fIAS\fR, and the AST Marker stack \fIMS\fR\&. .TP \fBias_push\fR This instruction pushes the semantic value \fISV\fR on the AST stack \fIAS\fR\&. .TP \fBias_mark\fR This instruction pushes a marker for the current state of the AST stack \fIAS\fR on the AST Marker stack \fIMS\fR\&. .TP \fBias_mrewind\fR This instruction pops an entry from the AST Marker stack \fIMS\fR and then proceeds to pop entries from the AST stack \fIAS\fR until the state represented by the popped marker has been reached again\&. Nothing is done if the AST stack \fIAS\fR is already smaller than indicated by the popped marker\&. .TP \fBias_mpop\fR This instruction pops an entry from the AST Marker stack \fIMS\fR and discards it\&. .PP .SH "BUGS, IDEAS, FEEDBACK" This document, and the package it describes, will undoubtedly contain bugs and other problems\&. Please report such in the category \fIgrammar_me\fR of the \fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&. Please also report any ideas for enhancements you may have for either package and/or documentation\&. .SH KEYWORDS grammar, parsing, virtual machine .SH CATEGORY Grammars and finite automata .SH COPYRIGHT .nf Copyright (c) 2005 Andreas Kupries .fi