#charset "us-ascii"
/*
* Copyright (c) 2000, 2006 Michael J. Roberts
*
* This file is part of TADS 3.
*
* This header defines the Dictionary intrinsic class.
*/
#ifndef _DICT_H_
#define _DICT_H_
/* include our base class definition */
#include "systype.h"
/*
* The Dictionary intrinsic class is a specialized lookup table class
* designed for storing the vocabulary table for a parser. Dictionary
* works closely with GrammarProd to supply the vocabulary tokens for the
* productions.
*
* The main difference between Dictionary and a more general hash table is
* that Dictionary tags each vocabulary word with a type; for our purposes,
* the type is the vocabulary property (&noun, &adjective, etc) that
* associates the word with an object.
*/
intrinsic class Dictionary 'dictionary2/030000': Object
{
/*
* Constructor:
*
* new Dictionary() - creates a dictionary with a default comparator,
* which matches strings exactly (note that upper-case and lower-case
* letters are considered distinct)
*
* new Dictionary(compObj) - create a dictionary with the given
* comparator object. A comparator is an object that implements the
* comparator interface - see below for details. When searching the
* dictionary (with findWord, for example), we use the comparator
* object to determine if the string beings sought matches a dictionary
* string.
*/
/*
* Set the comparator object. This defines how words are compared.
* The object must provide the following methods, which comprise the
* "comparator" interface. Note that there's no class that defines
* this interface; this is simply a set of methods that we define here,
* and which the supplied object must define.
*
* calcHash(str) - returns an integer giving the hash value of the
* given string. The purpose of the hash value is to arbitrarily
* partition the search space, so that we can search only a small
* subset of the dictionary when looking for a particular string. It
* is desirable for hash values to distribute uniformly for a given set
* of strings. It's also highly desirable for the hash computation to
* be inexpensive (i.e., to run fast), since the whole point of the
* hash is to reduce the amount of time it takes to find a string; if
* it takes longer to compute the hash value than it would to search
* every string in the table, then we don't come out ahead using the
* hash.
*
* matchValues(inputStr, dictStr) - compare the given input string with
* the given dictionary string, and return a result indicating whether
* or not they match for the purposes of the comparator. A return
* value of zero or nil indicates that the values do not match; any
* other return value indicates a match.
*
* Typically, matchValues() will return a non-zero integer to indicate
* a match and to encode additional information about the match using a
* bitwise-OR'd combination of flag values. For example, a comparator
* that allows case folding could use bit flag 0x0001 to indicate any
* match, and bit flag 0x0002 to indicate a match where the case of one
* or more input letters did not match the case of the corresponding
* letters in the dictionary string. So, a return value of 0x0001
* would indicate an exact match, and 0x0003 would indicate a match
* with case differences.
*
* Note that slight asymmetry in the matchValues() arguments: we
* specifically designate one string the input string and one the
* dictionary string. This allows for asymmetric comparisons, which
* are desirable in some cases; it is sometimes desirable to allow an
* input string to match a dictionary string even when the input string
* is slightly different. For example, we might want to allow the user
* to type only the first six or eight characters of a string in the
* dictionary, to save typing; or, we might want to allow a user to
* enter unaccented letters and still match dictionary words containing
* the corresponding letters with accents.
*
* Important: Note that, although the hash value computation is up to
* the implementing object to define, we impose one requirement. It is
* REQUIRED that for any two strings s1 and s2, if matchValues(s1, s2)
* indicates a match (i.e., returns a value other than 0 or nil), then
* calcHash(s1) MUST EQUAL calcHash(s2). (This does NOT mean that two
* strings with equal hash values must be equal, or, equivalently, that
* two unequal strings must have different hash values. Hash
* collisions are explicitly allowed, so two strings that don't match
* can still have the same hash value.)
*/
setComparator(compObj);
/*
* Find a word; returns a list giving the objects associated with the
* string in the dictionary. If voc_prop is specified, only objects
* associated with the word by the given vocabulary property are
* returned. We match the string using the comparator defined for the
* dictionary.
*
* The return value is a list consisting of pairs of entries. The
* first element of each pair is the matching object, and the second is
* gives the comparator result for matching the word. If we use a
* StringComparator, this will be a non-zero integer value giving
* information on truncation, case folding, and any equivalence
* mappings defined in the comparator. If the comparator is a custom
* object, then the second element of the pair will be whatever the
* custom comparator's matchValues() method returned for matching the
* value for that dictionary entry.
*
* The reason for giving a matchValues() return value for every
* individual match is that the same input string 'str' might match
* multiple entries in the dictionary. For example, the same string
* might match one word exactly and one with truncation. The match
* result code lets the caller determine if some matches are "better"
* than others, based on how the string matched for each individual
* object entry.
*/
findWord(str, voc_prop?);
/*
* Add a word to the dictionary, associating the given object with the
* given string and property combination.
*/
addWord(obj, str, voc_prop);
/*
* Remove the given word association from the dictionary. This
* removes only the association for the given object; other objects
* associated with the same word are not affected.
*/
removeWord(obj, str, voc_prop);
/*
* Check to see if the given string 'str' is defined in the dictionary.
* Returns true if the word is defined, nil if not.
*
* If the 'filter' argument is provided, it gives a callback function
* that is invoked to determine whether or not to count a particular
* word in the dictionary as a match. The callback is invoked with one
* argument: (filter)(match), where 'match' is the result of the
* comparator's matchValues(str,dstr) method, where 'dstr' is a
* dictionary string matching 'str'. The filter function returns true
* if the string should be counted as a match, nil if not. The return
* value of isWordDefined thus will be true if the filter function
* returns true for at least one match, nil if not. The purpose of the
* filter function is to allow the caller to impose a more restrictive
* condition than the dictionary's current comparator does; for
* example, the caller might use the filter to determine if the
* dictionary contains any matches for 'str' that match without any
* truncation.
*/
isWordDefined(str, filter?);
/*
* Invoke the callback func(str, obj, prop) for each word in the
* dictionary. Note that the callback can be invoked with a single
* string multiple times, since the callback is invoked once per
* word/object/property association; in other words, the callback is
* invoked once for each association created with addWord() or during
* compilation.
*/
forEachWord(func);
}
/*
* We rely on certain methods defined by the comparator interface, so
* export those method names.
*/
property calcHash, matchValues;
export calcHash 'IfcComparator.calcHash';
export matchValues 'IfcComparator.matchValues';
#endif /* _DICT_H_ */
TADS 3 Library Manual
Generated on 9/15/2006 from TADS version 3.0.12