[//000000001]: # (grammar::aycock \- Aycock\-Horspool\-Earley parser generator for Tcl) [//000000002]: # (Generated from file 'aycock\.man' by tcllib/doctools with format 'markdown') [//000000003]: # (Copyright © 2006 by Kevin B\. Kenny ) [//000000004]: # (Redistribution permitted under the terms of the Open Publication License ) [//000000005]: # (grammar::aycock\(n\) 1\.0 tcllib "Aycock\-Horspool\-Earley parser generator for Tcl")
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# NAME grammar::aycock \- Aycock\-Horspool\-Earley parser generator for Tcl # Table Of Contents - [Table Of Contents](#toc) - [Synopsis](#synopsis) - [Description](#section1) - [PROCEDURES](#section2) - [OBJECT COMMAND](#section3) - [DESCRIPTION](#section4) - [EXAMPLE](#section5) - [KEYWORDS](#section6) - [Keywords](#keywords) - [Category](#category) - [Copyright](#copyright) # SYNOPSIS package require Tcl 8\.5 package require grammar::aycock ?1\.0? [__::aycock::parser__ *grammar* ?__\-verbose__?](#1) [*parserName* __parse__ *symList* *valList* ?*clientData*?](#2) [*parserName* __destroy__](#3) [*parserName* __terminals__](#4) [*parserName* __nonterminals__](#5) [*parserName* __save__](#6) # DESCRIPTION The __grammar::aycock__ package implements a parser generator for the class of parsers described in John Aycock and R\. Nigel Horspool\. Practical Earley Parsing\. *The Computer Journal,* *45*\(6\):620\-630, 2002\. [http://citeseerx\.ist\.psu\.edu/viewdoc/summary?doi=10\.1\.1\.12\.4254](http://citeseerx\.ist\.psu\.edu/viewdoc/summary?doi=10\.1\.1\.12\.4254) # PROCEDURES The __grammar::aycock__ package exports the single procedure: - __::aycock::parser__ *grammar* ?__\-verbose__? Generates a parser for the given *grammar*, and returns its name\. If the optional __\-verbose__ flag is given, dumps verbose information relating to the generated parser to the standard output\. The returned parser is an object that accepts commands as shown in [OBJECT COMMAND](#section3) below\. # OBJECT COMMAND - *parserName* __parse__ *symList* *valList* ?*clientData*? Invokes a parser returned from __::aycock::parser__\. *symList* is a list of grammar symbols representing the terminals in an input string, and *valList* is a list of their semantic values\. The result is the semantic value of the entire string when parsed\. - *parserName* __destroy__ Destroys a parser constructed by __::aycock::parser__\. - *parserName* __terminals__ Returns a list of terminal symbols that may be presented in the *symList* argument to the __parse__ object command\. - *parserName* __nonterminals__ Returns a list of nonterminal symbols that were defined in the parser's grammar\. - *parserName* __save__ Returns a Tcl script that will reconstruct the parser without needing all the mechanism of the parser generator at run time\. The reconstructed parser depends on a set of commands in the package __grammar::aycock::runtime__, which is also automatically loaded when the __grammar::aycock__ package is loaded\. # DESCRIPTION The __grammar::aycock::parser__ command accepts a grammar expressed as a Tcl list\. The list must be structured as the concatenation of a set of *rule*s\. Each *rule* comprises a variable number of elements in the list: - The name of the nonterminal symbol that the rule reduces\. - The literal string, __::=__ - Zero or more names of terminal or nonterminal symbols that comprise the right\-hand\-side of the rule\. - Finally, a Tcl script to execute when the rule is reduced\. Within the given script, a variable called __\___ contains a list of the semantic values of the symbols on the right\-hand side\. The value returned by the script is expected to be the semantic value of the left\-hand side\. If the *clientData* parameter was passed to the __parse__ method, it is available in a variable called __clientData__\. It is permissible for the script to be the empty string\. In this case, the semantic value of the rule will be the same as the semantic value of the first symbol on the right\-hand side\. If the right\-hand side is also empty, the semantic value will be the empty string\. Parsing is done with an Earley parser, which is not terribly efficient in speed or memory consumption, but which deals effectively with ambiguous grammars\. For this reason, the __grammar::aycock__ package is perhaps best adapted to natural\-language processing or the parsing of extraordinarily complex languages in which ambiguity can be tolerated\. # EXAMPLE The following code demonstrates a trivial desk calculator, admitting only __\+__, __\*__ and parentheses as its operators\. It also shows the format in which the lexical analyzer is expected to present terminal symbols to the parser\. set p [aycock::parser { start ::= E {} E ::= E + T {expr {[lindex $_ 0] + [lindex $_ 2]}} E ::= T {} T ::= T * F {expr {[lindex $_ 0] * [lindex $_ 2]}} T ::= F {} F ::= NUMBER {} F ::= ( E ) {lindex $_ 1} }] puts [$p parse {( NUMBER + NUMBER ) * ( NUMBER + NUMBER ) } {{} 2 {} 3 {} {} {} 7 {} 1 {}}] $p destroy The example, when run, prints __40__\. # KEYWORDS Aycock, Earley, Horspool, parser, compiler # KEYWORDS [ambiguous](\.\./\.\./\.\./\.\./index\.md\#ambiguous), [aycock](\.\./\.\./\.\./\.\./index\.md\#aycock), [earley](\.\./\.\./\.\./\.\./index\.md\#earley), [grammar](\.\./\.\./\.\./\.\./index\.md\#grammar), [horspool](\.\./\.\./\.\./\.\./index\.md\#horspool), [parser](\.\./\.\./\.\./\.\./index\.md\#parser), [parsing](\.\./\.\./\.\./\.\./index\.md\#parsing), [transducer](\.\./\.\./\.\./\.\./index\.md\#transducer) # CATEGORY Grammars and finite automata # COPYRIGHT Copyright © 2006 by Kevin B\. Kenny Redistribution permitted under the terms of the Open Publication License