158 lines
5.4 KiB
C++
158 lines
5.4 KiB
C++
/*
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******************************************************************************
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* Copyright (C) 2005, International Business Machines Corporation and *
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* others. All Rights Reserved. *
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******************************************************************************
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*/
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/*
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WBNF, Weighted BNF, is an extend BNF. The most difference between WBNF
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and standard BNF is the WBNF accepts weight for its alternation items.
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The weight specifies the opportunity it will be selected.
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The purpose of WBNF is to help generate a random string from a given grammar
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which can be described with standard BNF. The introduction of 'weight'
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is to guide the generator to give the specific parts different chances to be
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generated.
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Usually, the user gives LanguageGenerator the grammar description in WBNF,
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then LanguageGenerator will generate a random string on every next() call.
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The return code of parseBNF() can help user to determine the error,
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either in the grammar description or in the WBNF parser itself.
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The grammar of WBNF itself can be described in standard BNF,
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escaping = _single character with a leading back slash, either inside or outside quoting_
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quoting = _quoted with a pair of single quotation marks_
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string = string alphabet | string digit | string quoting | string escaping |
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alphabet | quoting | escaping
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alphabet =
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digit =
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integer = integer digit | digit
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weight = integer %
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weight-list = weight-list weight | weight
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var = var alphabet | var digit | $ alphabet
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var-defs = var-defs var-def | var-def
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var-def = var '=' definition;
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alternation = alternation '|' alt-item | alt-item
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alt-item = sequence | sequence weight
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sequence = sequence modified | modified
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modified = core | morph | quote | repeat
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morph = modified ~
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quote = modified @
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repeat = modified quantifier | modified quantifier weight-list
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quantifier = ? | * | + | { integer , integer} | {integer, } | {integer}
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core = var | string | '(' definition ')'
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definition = core | modified | sequence | alternation
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definition = alternation
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Remarks:
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o Following characters are literals in preceding definition
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but are syntax symbols in WBNF
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% $ ~ @ ? * + { } ,
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o Following character are syntax symbols in preceding definition
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(sapce) contact operation, or separators to increase readability
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= definition
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| selection operation
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( ) precedence select
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' ' override special-character to plain character
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o the definition of 'escaping' and 'quoting' are preceding definition text
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o infinite is actually a predefine value PSEUDO_INFINIT defined in this file
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o if weight is not presented in "alt-item' and 'repeat',
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a default weight DEFAULT_WEIGHT defined in this file is used
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o * == {0, }
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+ == {1, }
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? == {0, 1}
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o the weight-list for repeat assigns the weights for repeat itmes one by one
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demo{1,3} 30% 40% 100% == (demo)30% | (demodemo)40% | (demodemodemo)100%
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To find more explain of the weight-list, please see the LIMITATION of the grammar
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o but the weight-list for question mark has different meaning
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demo ? 30% != demo{0,1} 30% 100%
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demo ? 30% == demo{0,1} 70% 30%
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the 70% is calculated from (DEFAULT_WEIGHT - weight)
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Known LIMITATION of the grammar
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For 'repeat', the parser will eat up as much as possible weights at one time,
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discard superfluous weights if it is too much,
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fill insufficient weights with default weight if it is too less.
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This behavior means following definitions are equal
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demo{1,3} 30% 40% 100%
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demo{1,3} 30% 40% 100% 50%
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demo{1,3} 30% 40%
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This behavior will cause a little confusion when defining an alternation
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demo{1,3} 30% 40% 100% 50% | show 20%
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is interpreted as
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(demo{1,3} 30% 40% 100%) 100% | show 20%
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not
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(demo{1,3} 30% 40% 100%) 50% | show 20%
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to get an expected definition, please use parentheses.
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Known LIMITATION of current implement
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Due to the well known point alias problem, current Parser will be effectively
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crashed if the definition looks like
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$a = demo;
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$b = $a;
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$c = $a;
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or
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$a = demo;
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$b = $a $a;
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or
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$a = demo;
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$b = $b $a;
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The crash will occur at delete operation in destructor or other memory release code.
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Several plans are on hard to fix the problem. Use a smart point with reference count,
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or use a central memory management solution. But now, it works well with collation
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monkey test, which is the only user for WBNF.
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*/
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#ifndef _WBNF
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#define _WBNF
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#include "unicode/utypes.h"
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const int DEFAULT_WEIGHT = 100;
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const int PSEUDO_INFINIT = 200;
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class LanguageGenerator_impl;
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class LanguageGenerator{
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LanguageGenerator_impl * lang_gen;
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public:
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enum PARSE_RESULT {OK, BNF_DEF_WRONG, INCOMPLETE, NO_TOP_NODE};
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LanguageGenerator();
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~LanguageGenerator();
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PARSE_RESULT parseBNF(const char *const bnf_definition /*in*/, const char *const top_node/*in*/, UBool debug=FALSE);
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const char *next(); /* Return a null-terminated c-string. The buffer is owned by callee. */
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};
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void TestWbnf(void);
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#endif /* _WBNF */
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