# gramprod.t | documentation

    #charset "us-ascii"

    /*
     *   Copyright (c) 2005, 2006 Michael J. Roberts
     *
     *   This file is part of TADS 3.
     *
     *   This module defines some classes used by the GrammarProd intrinsic
     *   class.
     */

    #include <tads.h>
    #include <gramprod.h>

    /* ------------------------------------------------------------------------ */
    /*
     *   GrammarProd descriptor classes.  The GrammarProd intrinsic class's
     *   getGrammarInfo() method uses these classes to build its description of
     *   a grammar production.
     */

    /* export the classes so the intrinsic class can find them */
    export GrammarAltInfo 'GrammarProd.GrammarAltInfo';
    export GrammarAltTokInfo 'GrammarProd.GrammarAltTokInfo';

    /*
     *   Rule alternative descriptor.  This describes one alternative in a
     *   grammar production.  An alternative is one complete list of matchable
     *   tokens.
     *
     *   In a 'grammar' statement, alternatives are delimited by '|' symbols at
     *   the top level.  Each group of tokens set off by '|' symbols is one
     *   alternative.
     *
     *   When '|' symbols are grouped with parentheses in a 'grammar'
     *   statement, the compiler "flattens" the grouping by expanding out the
     *   parenthesized groups until it has entirely top-level alternatives.
     *   So, at the level of a GrammarProd object, there's no such thing as
     *   parentheses or nested '|' symbols.
     */
    class GrammarAltInfo: object
        /*
         *   Constructor.  GrammarProd.getGrammarInfo() calls this once for
         *   each alternative making up the production, passing in the values
         *   that define the alternative.  Note that we have a '...' in our
         *   argument list so that we'll be compatible with any future
         *   GrammarProd versions that add additional arguments - we won't do
         *   anything with the extra arguments, but we'll harmlessly ignore
         *   them, so code compiled with this library version will continue to
         *   work correctly.
         */
        construct(score, badness, matchObj, toks, ...)
        {
            /* stash away the information */
            gramBadness = badness;
            gramMatchObj = matchObj;
            gramTokens = toks;
        }

        /*
         *   The 'badness' value associated with the alternative.  A value of
         *   zero means that there's no badness.
         */
        gramBadness = 0

        /*
         *   the "match object" class - this is the class that
         *   GrammarProd.parseTokens() instantiates to represent a match to
         *   this alternative in the match list that the method returns
         */
        gramMatchObj = nil

        /*
         *   The token descriptor list.  This is a list of zero or more
         *   GrammarAltTokInfo objects describing the tokens making up this
         *   rule.
         */
        gramTokens = []
    ;

    /*
     *   Grammar rule token descriptor.  GrammarProd.getGrammarInfo()
     *   instantiates one of these objects to represent each token slot in an
     *   alternative; a GrammarAltInfo object's gramTokens property has a list
     *   of these objects.
     */
    class GrammarAltTokInfo: object
        /*
         *   Constructor.  GrammarProd.getGrammarInfo() calls this once for
         *   each token in each alternative in the production, passing in
         *   values to fully describe the token slot: the target property (in a
         *   'grammar' statement, this is the property after a '->' symbol);
         *   the token type; and extra information that depends on the token
         *   type.  Note that we use '...' at the end of the argument list so
         *   that we'll be compatible with any future changes to GrammarProd
         *   that add more arguments to this method.
         */
        construct(prop, typ, info, ...)
        {
            /* remember the information */
            gramTargetProp = prop;
            gramTokenType = typ;
            gramTokenInfo = info;
        }

        /*
         *   The target property - this is the property of the *match object*
         *   that will store the match information for the token.  In a
         *   'grammar' statement, this is the property after the '->' symbol
         *   for this token.
         */
        gramTargetProp = nil

        /*
         *   The token type.  This is one of the GramTokTypeXxx values (see
         *   gramprod.h) indicating what kind of token slot this is.
         */
        gramTokenType = nil

        /*
         *   Detailed information for the token slot, which depends on the
         *   token type:
         *
         *   GramTokTypeProd - this gives the GrammarProd object defining the
         *   sub-production that this token slot matches
         *
         *   GramTokTypeSpeech - this is the property ID giving the
         *   part-of-speech property that this token slot matches
         *
         *   GramTokTypeNSpeech - this is a list of property IDs giving the
         *   part-of-speech properties that this token slot matches
         *
         *   GramTokTypeLiteral - this is a string giving the literal that this
         *   slot matches
         *
         *   GramTokTypeTokEnum - this is the enum value giving the token type
         *   that this slot matches
         *
         *   GramTokTypeStar - no extra information (the value will be nil)
         */
        gramTokenInfo = nil
    ;

    /*
     *   Dynamic match object interface.  This is a mix-in class that should be
     *   used as a superclass for any class used as the match object when
     *   creating new alternatives dynamically with GrammarProd.addAlt().
     *
     *   This class provides an implementation of grammarInfo() that works like
     *   the version the compiler generates for static match objects.  In this
     *   case, we use the grammarAltProps information that addAlt() stores in
     *   the match object.
     */
    class DynamicProd: object
        /*
         *   Generate match information.  This returns the same information
         *   that grammarInfo() returns for match objects that the compiler
         *   generates for static 'grammar' statements.
         */
        grammarInfo()
        {
            return [grammarTag] + grammarAltProps.mapAll({ p: self.(p) });
        }

        /*
         *   grammarTag - the name for the collection of alternatives
         *   associated with the match object.  This name is primarily for
         *   debugging purposes; it appears as the first element of the
         *   grammarInfo() result list.
         */
        grammarTag = 'new-alt'

        /*
         *   grammarAltProps - the list of "->" properties used in all of the
         *   alternatives associated with this match object.  addAlts() stores
         *   this list automatically - there's no need to create it manually.
         */
        grammarAltProps = []
    ;

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