# tok.t | documentation

    #charset "us-ascii"

    /*
     *   Tokenizer - customizable tokenizer class for use with the intrinsic
     *   class 'grammar-production' parser.
     *
     *   This tokenizer implementation is parameterized with a set of rules
     *   (see below); a basic set of rules is provided, but users can
     *   customize the tokenizer quite extensively simply by subclassing the
     *   Tokenizer class and overriding the 'rules_' property with a new set
     *   of rules declarations.
     */

    #include "tads.h"
    #include "t3.h"
    #include "dict.h"
    #include "tok.h"
    #include "vector.h"

    /* ------------------------------------------------------------------------ */
    /*
     *   Tokenizer exceptions
     */

    /*
     *   base class for all tokenizer errors (to allow blanket 'catch')
     */
    class TokenizerError: Exception
        displayException() { "Tokenizer exception"; }
    ;

    /*
     *   no match for token
     */
    class TokErrorNoMatch: TokenizerError
        construct(str)
        {
            /* remember the full remaining text */
            remainingStr_ = str;

            /*
             *   for convenience, separately remember the single character
             *   that we don't recognize - this is simply the first character
             *   of the rest of the line
             */
            curChar_ = str.substr(1, 1);
        }

        displayException()
            { "Tokenizer error: unexpected character '<<curChar_>>'"; }

        /*
         *   The remainder of the string.  This is the part that couldn't be
         *   matched; we were successful in matching up to this point.
         */
        remainingStr_ = nil

        /* current character (first character of remainingStr_) */
        curChar_ = nil
    ;

    /* ------------------------------------------------------------------------ */
    /*
     *   Basic token types
     */

    /* word */
    enum token tokWord;

    /* quoted string */
    enum token tokString;

    /* punctuation */
    enum token tokPunct;

    /* integer number */
    enum token tokInt;

    /* ------------------------------------------------------------------------ */
    /*
     *   Tokenizer base class
     */
    class Tokenizer: object
        /*
         *   Tokenizing rules.  The subclass can override this to specify a
         *   list that defines different tokenization rules.  Each entry in the
         *   master rules_ list is one rule.  Each rule is a list consisting of
         *   the name of the rule; the pattern to match for the rule; the token
         *   type (an 'enum token') to use when the rule is matched; the value
         *   computation rule; and the value test rule.
         *
         *   The name of a rule is just an arbitrary string to identify the
         *   rule.  This can be used to insert new rules in order relative to
         *   known existing rules, or to delete known existing rules.
         *
         *   If the value computation rule is nil, we'll just use the matching
         *   text as the token value.  If the value rule is a string, we'll use
         *   the string as a replacement pattern (with rexReplace).  If it's a
         *   property ID, we'll invoke the property of self with the following
         *   arguments:
         *
         *   txt, typ, toks
         *
         *   'txt' is the matched text; 'typ' is the token type from the rule;
         *   and 'toks' is a vector to which the new token or tokens are to be
         *   added.  The routine is responsible for adding the appropriate
         *   values to the result list.  Note that the routine can add more
         *   than one token to the results if desired.
         *
         *   If the value test rule is non-nil, it must be either a method or a
         *   function; we'll call the method or function to test to see if the
         *   matched value is valid.  We'll call the method (on self) with the
         *   matching text as the argument; if the method returns true, the
         *   rule matches, otherwise the rule fails, and we'll continue looking
         *   for another rule as though we hadn't matched the rule's regular
         *   expression in the first place.  This can be used for rules that
         *   require more than a simple regular expression match; for example,
         *   the value test can be used to look up the match in a dictionary,
         *   so that the rule only matches tokens that are defined in the
         *   dictionary.
         */
        rules_ = static
        [
            /* skip whitespace */
            ['whitespace', R'<Space>+', nil, &tokCvtSkip, nil],

            /* certain punctuation marks */
            ['punctuation', R'[.,;:?!]', tokPunct, nil, nil],

            /*
             *   Words - note that we convert everything to lower-case.  A
             *   word must start with an alphabetic character, but can contain
             *   alphabetics, digits, hyphens, and apostrophes after that.
             */
            ['word', R'<Alpha>(<AlphaNum>|[-\'])*', tokWord, &tokCvtLower, nil],

            /* strings */
            ['string single-quote', R'\'(.*)\'', tokString, nil, nil],
            ['string double-quote', R'"(.*)"', tokString, nil, nil],

            /* integer numbers */
            ['integer', R'[0-9]+', tokInt, nil, nil]
        ]

        /*
         *   Insert a new rule before or after the existing rule with the name
         *   'curName'.  If 'curName' is nil, or rule is found with the given
         *   name, we'll insert the new rule at the end of the list.  'rule'
         *   must be a list with the standard elements for a tokenizer rule.
         *   'after' is nil to insert the new rule before the given existing
         *   rule, true to insert after it.
         */
        insertRule(rule, curName, after)
        {
            local idx;

            /*
             *   if the name of an existing rule was supplied, find the
             *   existing rule with the given name
             */
            idx = nil;
            if (curName != nil)
                idx = rules_.indexWhich({x: tokRuleName(x) == curName});

            /* if we didn't find curName, insert at the end of the list */
            if (idx == nil)
                idx = rules_.length();

            /* if we're inserting after the given element, adjust the index */
            if (after)
                ++idx;

            /* insert the new rule */
            insertRuleAt(rule, idx);
        }

        /*
         *   Insert a rule at the given index in our rules list.  'rule' must
         *   be a list with the standard elements for a tokenizer rule.  'idx'
         *   is the index of the new rule; we'll insert before the existing
         *   element at this index; so if 'idx' is 1, we'll insert before the
         *   first existing rule.
         */
        insertRuleAt(rule, idx)
        {
            /* insert the rule */
            rules_ = rules_.insertAt(idx, rule);
        }

        /*
         *   Delete a rule by name.  This finds the rule with the given name
         *   and removes it from the list.
         */
        deleteRule(name)
        {
            local idx;

            /* find the rule with the given name */
            idx = rules_.indexWhich({x: tokRuleName(x) == name});

            /* if we found the named element, remove it from the list */
            if (idx != nil)
                deleteRuleAt(idx);
        }

        /* delete the rule at the given index */
        deleteRuleAt(idx)
        {
            /* delete the rule */
            rules_ = rules_.removeElementAt(idx);
        }

        /* convert a string to lower-case (for value computation rules) */
        tokCvtLower(txt, typ, toks)
        {
            /* add the lower-cased version of the string to the result list */
            toks.append([txt.toLower(), typ, txt]);
        }

        /*
         *   processing routine to skip a match - this is used for whitespace
         *   and other text that does not result in any tokens in the result
         *   list
         */
        tokCvtSkip(txt, typ, toks)
        {
            /* simply skip the text without generating any new tokens */
        }

        /*
         *   Tokenize a string.  If we find text that we can't match to any of
         *   the rules, we'll throw an exception (TokErrorNoMatch).  If we
         *   succeed in tokenizing the entire string, we'll return a list with
         *   one element per token.  Each element of the main list is a
         *   sublist with the following elements describing a token:
         *
         *   - The first element gives the token's value.
         *
         *   - The second element the token type (given as a token type enum
         *   value).
         *
         *   - The third element the original token strings, before any
         *   conversions or evaluations were performed.  For example, this
         *   maintains the original case of strings that are lower-cased for
         *   the corresponding token values.
         */
        tokenize(str)
        {
            local toks = new Vector(32);
            local startIdx = 1;
            local len = str.length();

            /* keep going until we run out of string */
        mainLoop:
            while (startIdx <= len)
            {
                /* run through the rules in sequence until we match one */
            ruleLoop:
                for (local i = 1, local cnt = rules_.length() ; i <= cnt ; ++i)
                {
                    local cur;
                    local match;
                    local val;

                    /* get the current rule */
                    cur = rules_[i];

                    /* check for a match to the rule's pattern */
                    match = rexMatch(tokRulePat(cur), str, startIdx);
                    if (match != nil && match > 0)
                    {
                        local test;
                        local txt;
                        local typ;

                        /* get the matching text */
                        txt = str.substr(startIdx, match);

                        /*
                         *   if there's a value test, invoke it to determine
                         *   if the token really matches
                         */
                        if ((test = tokRuleTest(cur)) != nil)
                        {
                            local accept;

                            /* check what kind of test function we have */
                            switch (dataType(test))
                            {
                            case TypeFuncPtr:
                            case TypeObject:
                                /* it's a function or anonymous function */
                                accept = (test)(txt);
                                break;

                            case TypeProp:
                                /* it's a method */
                                accept = self.(test)(txt);
                                break;

                            default:
                                /* consider anything else to be accepted */
                                accept = true;
                                break;
                            }

                            /*
                             *   if the value test failed, it means that the
                             *   token doesn't match this rule after all -
                             *   ignore the regex match and keep searching for
                             *   another rule
                             */
                            if (!accept)
                                continue ruleLoop;
                        }

                        /* get the type of the token from the rule */
                        typ = tokRuleType(cur);

                        /* get this value processing rule */
                        val = tokRuleVal(cur);

                        /* determine what value to use */
                        switch(dataTypeXlat(val))
                        {
                        case TypeNil:
                            /* use the matching text verbatim */
                            toks.append([txt, typ, txt]);
                            break;

                        case TypeProp:
                            /*
                             *   invoke the property - it's responsible for
                             *   adding the token or tokens to the results
                             *   lists
                             */
                            self.(val)(txt, typ, toks);
                            break;

                        case TypeSString:
                            /* it's a regular expression replacement */
                            toks.append(
                                [rexReplace(tokRulePat(cur),
                                            txt, val, ReplaceOnce),
                                 typ, txt]);
                            break;

                        case TypeFuncPtr:
                            /* invoke the function */
                            (val)(txt, typ, toks);
                            break;

                        default:
                            /*
                             *   use any other value exactly as given in
                             *   the rule
                             */
                            toks.append([val, typ, txt]);
                            break;
                        }

                        /*
                         *   continue the search at the next character after
                         *   the end of this token
                         */
                        startIdx += match;

                        /* start over with the rest of the string */
                        continue mainLoop;
                    }
                }

                /*
                 *   We failed to find a match for this part of the string.
                 *   Throw an exception and let the caller figure out what to
                 *   do.  The exception parameter gives the rest of the
                 *   string, so the caller can display a suitable error
                 *   message if desired.
                 */
                throw new TokErrorNoMatch(str.substr(startIdx));
            }

            /* we're done with the string - return out value and type lists */
            return toks.toList();
        }
    ;

    /* ------------------------------------------------------------------------ */
    /*
     *   Test Section
     */

    #ifdef TOK_TEST

    main(args)
    {
        "Enter text to tokenize.  Type Q or QUIT when done. ";
        for (;;)
        {
            local str, toks;

            /* read a string */
            "\b>";
            str = inputLine();

            /* catch tokenization errors */
            try
            {
                /* tokenize the string */
                toks = Tokenizer.tokenize(str);

                /* if the first token is 'quit', we're done */
                if (toks.length() > 0
                    && getTokType(toks[1]) == tokWord
                    && (getTokVal(toks[1])== 'quit' || getTokVal(toks[1]) == 'q'))
                {
                    /* they want to stop - exit the command loop */
                    break;
                }

                /* display the tokens */
                for (local i = 1, local cnt = toks.length() ; i <= cnt ; ++i)
                    "(<<getTokVal(toks[i])>>) ";
            }
            catch (TokErrorNoMatch err)
            {
                "Unrecognized punctuation: <<err.remainingStr_.substr(1, 1)>>";
            }
        }
    }

    #endif /* TOK_TEST */

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