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+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+
+Yacc is a version of yacc for Go. It is run with the command
+	go tool yacc args...
+It is written in Go and generates parsers written in Go.
+
+It is largely transliterated from the Inferno version written in Limbo
+which in turn was largely transliterated from the Plan 9 version
+written in C and documented at
+
+	http://plan9.bell-labs.com/magic/man2html/1/yacc
+
+Adepts of the original yacc will have no trouble adapting to this
+form of the tool.
+
+The file units.y in this directory is a yacc grammar for a version of
+the Unix tool units, also written in Go and largely transliterated
+from the Plan 9 C version. It needs the flag "-p units_" (see
+below).
+
+The generated parser is reentrant. Parse expects to be given an
+argument that conforms to the following interface:
+
+	type yyLexer interface {
+		Lex(lval *yySymType) int
+		Error(e string)
+	}
+
+Lex should return the token identifier, and place other token
+information in lval (which replaces the usual yylval).
+Error is equivalent to yyerror in the original yacc.
+
+Code inside the parser may refer to the variable yylex,
+which holds the yyLexer passed to Parse.
+
+Multiple grammars compiled into a single program should be placed in
+distinct packages.  If that is impossible, the "-p prefix" flag to
+yacc sets the prefix, by default yy, that begins the names of
+symbols, including types, the parser, and the lexer, generated and
+referenced by yacc's generated code.  Setting it to distinct values
+allows multiple grammars to be placed in a single package.
+
+*/
+package documentation