# gramprod.h | documentation

    #charset "us-ascii"
    #pragma once

    /*
     *   Copyright (c) 2000, 2006 Michael J. Roberts
     *
     *   This file is part of TADS 3.
     *
     *   The header defines the GrammarProd intrinsic class and some associated
     *   properties and constants.
     */

    /* include our base class definition */
    #include "systype.h"

    /*
     *   The GrammarProd intrinsic class is a specialized type that's designed
     *   for creating parsers.  An object of this type is created automatically
     *   by the TADS 3 compiler for each 'grammar' statement.  This class
     *   encapsulates the prototype token list and mapping information defined in
     *   a 'grammar' statement, and provides a method to match its prototype to
     *   an input token string.
     *
     *   GrammarProd implements a "parser" in a limited computerese sense, which
     *   is essentially a program that produces "sentence diagrams" a la
     *   elementary school grammar lessons.  GrammarProd is thus only a small
     *   part of what we think of as "the parser" in an IF context.  The broader
     *   parser starts with the sentence diagrams that GrammarProd produces, and
     *   must then interpret their meanings and carry out the intentions they
     *   express.
     *
     *   Parsers built with GrammarProd trees can handle grammars with left or
     *   right recursion, and can handle ambiguous grammars (meaning that a
     *   single input can have multiple ways of matching the grammar).  This is
     *   especially important for natural language parsing, since virtually all
     *   natural languages have ambiguous grammars.  When a match is ambiguous, a
     *   GrammarProd parser builds all of the possible match trees, allowing you
     *   to choose the best match based on context and semantic content.
     *
     *   You can also create new productions dynamically with new GrammarProd().
     *   Use addAlt() to populate a new production with token matching rules.
     */
    intrinsic class GrammarProd 'grammar-production/030002': Object
    {
        /*
         *   Parse the token list, starting at this production, using the given
         *   dictionary to look up tokens.  Returns a list of match objects.  If
         *   there are no matches to the grammar, simply returns an empty list.
         */
        parseTokens(tokenList, dict);

        /*
         *   Retrieve a detailed description of the production.  This returns a
         *   list of GrammarAltInfo objects that describe the rule alternatives
         *   that make up this production.
         */
        getGrammarInfo();

        /*
         *   Add a new alternative set of alternatives to the rule list for this
         *   grammar production.
         *
         *   'alt' is a string with the token list specifying the alternative(s)
         *   to add.  This uses the same syntax as the rule list in a static
         *   'grammar' statement.  You can use '|' symbols to add multiple
         *   alternatives.
         *
         *   'matchObj' is the match object class, which is the class of the
         *   object that parseTokens() reutrns in the match list to represent a
         *   match to this production.  This corresponds to the base class
         *   defined in a static 'grammar' statement.
         *
         *   'dict' is an optional Dictionary object.  Literal tokens used in the
         *   token list will be automatically added to the dictionary if they're
         *   not already defined.
         *
         *   'symtab' is an optional LookupTable with the global symbol table.
         *   This must be provided if any symbolic tokens are used in the rule
         *   list (property names, sub-production names, etc).  In most cases
         *   this is simply the symbol table that t3GetGlobalSymbols() returns
         *   during preinit.
         */
        addAlt(alt, matchObj, dict?, symtab?);

        /*
         *   Delete onen or more alternatives from the rule list for this grammar
         *   production.  'id' identifies the rule(s) to delete:
         *
         *   - By tag: if 'id' is a string, the method deletes each alternative
         *   whose match object's grammarTag property equals 'id'.  For static
         *   rules defined with 'grammar' statements, the compiler sets
         *   grammarTag to the tag used in the statement defining the rule.  This
         *   makes it easy to delete all of the rules defined by a given
         *   'grammar' statement.
         *
         *   - By match object class: if 'id' is an object, the method deletes
         *   every alternative whose match object equals 'id' or is a subclass of
         *   'id'.  This makes it easy to delete a group of dynamically added
         *   rules that share a match object.
         *
         *   - By index: if 'id' is an integer, it gives the index of the rule to
         *   delete.  This corresponds to an index in the list returned by
         *   getGrammarInfo().
         *
         *   'dict' is an optional Dictionary object to adjust for the deletion.
         *   If a non-nil 'dict' is given, we'll remove literals from the
         *   dictionary that were defined by the alternative and no longer used
         *   in the production.
         */
        deleteAlt(id, dict?);

        /*
         *   Delete all alternatives from the rule list for this grammar
         *   production.  This resets the rule to an empty production with no
         *   alternatives to match, which is convenient if you want to redefine
         *   the entire rule set with a subsequent addAlt() call.
         *
         *   'dict' is an optional Dictionary object to adjust for the deletion.
         *   If a non-nil 'dict' is given, we'll remove all of the production's
         *   literals from the dictionary.
         */
        clearAlts(dict?);
    }

    /*
     *   Token slot types.  Each token slot in an alternative has a type, which
     *   determines what it matches in an input token list.  getGrammarInfo()
     *   returns these type codes in the GrammarAltTokInfo objects.
     */

    #define GramTokTypeProd    1              /* token matches a sub-production */
    #define GramTokTypeSpeech  2     /* token matches a specific part of speech */
    #define GramTokTypeLiteral 3              /* token matches a literal string */
    #define GramTokTypeTokEnum 4            /* token matches a token class enum */
    #define GramTokTypeStar    5    /* token matches all remaining input tokens */
    #define GramTokTypeNSpeech 6      /* matches any of several parts of speech */

    /*
     *   Properties for the first and last token indices, and the complete
     *   original token list.
     *
     *   Each match tree object will have the firstTokenIndex and lastTokenIndex
     *   properties set to the bounding token indices for its subtree.  Each
     *   match tree object will also have tokenList set to the original token
     *   list passed to the parseTokens() that created the match tree, and
     *   tokenMatchList set to a list of the Dictionary's comparator's
     *   matchValues() result for each token match.
     */
    property firstTokenIndex, lastTokenIndex, tokenList, tokenMatchList;
    export firstTokenIndex 'GrammarProd.firstTokenIndex';
    export lastTokenIndex  'GrammarProd.lastTokenIndex';
    export tokenList       'GrammarProd.tokenList';
    export tokenMatchList  'GrammarProd.tokenMatchList';

    /*
     *   For alternatives created at run-time with addAlt(), the system maintains
     *   a list of all of the properties used in "->" expressions in all
     *   alternatives associated with a match object.  This list of properties is
     *   stored in the grammarAltProps of the match object.
     */
    property grammarAltProps;
    export grammarAltProps 'GrammarProd.altProps';

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