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https://github.com/golang/go
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71 lines
2.4 KiB
Go
71 lines
2.4 KiB
Go
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/*
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Goyacc is a version of yacc for Go.
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It is written in Go and generates parsers written in Go.
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Usage:
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goyacc args...
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It is largely transliterated from the Inferno version written in Limbo
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which in turn was largely transliterated from the Plan 9 version
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written in C and documented at
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https://9p.io/magic/man2html/1/yacc
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Adepts of the original yacc will have no trouble adapting to this
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form of the tool.
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The directory $GOPATH/src/golang.org/x/tools/cmd/goyacc/testdata/expr
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is a yacc program for a very simple expression parser. See expr.y and
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main.go in that directory for examples of how to write and build
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goyacc programs.
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The generated parser is reentrant. The parsing function yyParse expects
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to be given an argument that conforms to the following interface:
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type yyLexer interface {
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Lex(lval *yySymType) int
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Error(e string)
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}
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Lex should return the token identifier, and place other token
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information in lval (which replaces the usual yylval).
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Error is equivalent to yyerror in the original yacc.
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Code inside the grammar actions may refer to the variable yylex,
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which holds the yyLexer passed to yyParse.
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Clients that need to understand more about the parser state can
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create the parser separately from invoking it. The function yyNewParser
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returns a yyParser conforming to the following interface:
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type yyParser interface {
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Parse(yyLex) int
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Lookahead() int
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}
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Parse runs the parser; the top-level call yyParse(yylex) is equivalent
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to yyNewParser().Parse(yylex).
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Lookahead can be called during grammar actions to read (but not consume)
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the value of the current lookahead token, as returned by yylex.Lex.
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If there is no current lookahead token (because the parser has not called Lex
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or has consumed the token returned by the most recent call to Lex),
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Lookahead returns -1. Calling Lookahead is equivalent to reading
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yychar from within in a grammar action.
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Multiple grammars compiled into a single program should be placed in
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distinct packages. If that is impossible, the "-p prefix" flag to
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goyacc sets the prefix, by default yy, that begins the names of
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symbols, including types, the parser, and the lexer, generated and
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referenced by yacc's generated code. Setting it to distinct values
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allows multiple grammars to be placed in a single package.
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*/
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package main
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