goyacc: provide -p flag to set prefix for names.

This should allow multiple goyacc grammars to be
compiled into the same binary. There's a chance it
Fixes #1562.

R=rsc, r2
CC=golang-dev
https://golang.org/cl/4256044

src/cmd/goyacc/Makefile

@@ -11,7 +11,7 @@ GOFILES=\
 include ../../Make.cmd
 
 units: goyacc units.y
-	./goyacc units.y
+	./goyacc -p units_ units.y
 	$(GC) y.go
 	$(LD) -o units y.$O
 

src/cmd/goyacc/doc.go

@@ -17,7 +17,8 @@ Yacc adepts 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.
+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:
@@ -31,8 +32,14 @@ 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
+Code inside the parser may refer to the variable yylex,
 which holds the yyLexer passed to Parse.
 
+The "-p prefix" flag to goyacc sets the prefix, by default yy, that
+begins the names of symbols, including types, the parser, and the
+lexer, generated and referenced by goyacc's generated code.  Setting
+it to distinct values allows multiple grammars to be used in a
+single binary.
+
 */
 package documentation

src/cmd/goyacc/units.y

@@ -6,6 +6,9 @@
 // Distributed under the terms of the Lucent Public License Version 1.02
 // See http://plan9.bell-labs.com/plan9/license.html
 
+// Generate parser with prefix "units_":
+//	goyacc -p "units_"
+
 %{
 
 // units.y
@@ -215,7 +218,7 @@ expr0:
 
 type UnitsLex int
 
-func (UnitsLex) Lex(yylval *yySymType) int {
+func (UnitsLex) Lex(yylval *units_SymType) int {
 	var c, i int
 
 	c = peekrune
@@ -319,7 +322,7 @@ func main() {
 			continue
 		}
 		peekrune = ':'
-		yyParse(UnitsLex(0))
+		units_Parse(UnitsLex(0))
 	}
 
 	/*
@@ -340,7 +343,7 @@ func main() {
 		}
 		peekrune = '?'
 		nerrors = 0
-		yyParse(UnitsLex(0))
+		units_Parse(UnitsLex(0))
 		if nerrors != 0 {
 			continue
 		}