WG15 Defect Report Ref: 9945-2-93
Topic: yacc

This is an approved interpretation of 9945-2:1993.


Last update: 1997-05-20



	Topic:			yacc
	Relevant Sections:	A.

Defect Report:
	Date: Tue, 20 Dec 1994 14:09:54 -0800
	From: seizo@jurassic-50.Eng.Sun.COM (Seizo Sakurai)

A request for interpretation

A) The specific designation of the standard
	ISO/IEC 9945-2:1993
B) The specific subsection being questioned
	A.	yacc Code File
		Line 690-691
C) The applicable conditions for the case in questions
	The applicable condition is when yacc input
	file has the programs section. Please see Appendix 1
	attached to this note.
D) A suggested correction, if applicable
	Remove Line 690-691
E) Reson for the suggested correction
	1) There are quite many yacc input files assuming that
	   the program section is copied before yyparse().
	   If the program section needs to be copied after
	   yyparse(), then many of already written yacc input
	   files need to be modified.
	2) The line 936-941 says that
		"It is unspecified whether the program section
		 precedes or follows the semantic actions in the
		 output file; therefore, if the application
		 contains any macro definitions and declarations
		 intended to apply the code in the semantic actions,
		 it shall place them within %{ ... %} in the
		 declaration section."
	    The above says that "it is unspecified whether the
	    program section precedes or follows the semantic actions
	    in the output file;". Most of yacc implementation
	    places its semantic actions in yyparse() and the document
	    also mentions it. (Line 685-686) Therefore, there should be
	    no problem removing line 690-691.

Appendix 1: An example
	This yacc input file is a little example about the problem.

	From this input, yacc will generate a parser. The parser
	calls hello_world() when non-terminal sound is recognized.
	The parser also calls print_str() when ding is recognized.

		 * Declaration
		#include <stdio.h>
		char *hello_world(char *);
		%token DING
		%token DONG
		%token DELL
		sound:	ding DONG DELL
				hello_world("sound recognized\n");
		ding:	DING
				print_str("ding recognized\n");
		char *
		print_str(char *s)
			return (s);

	Yacc's output will have the following format. (This is y.tab.c by default.)

		1) Declaration section
			The beginning of y.tab.c is a copy of
			the input portion surrounded by %{ and %}.
			In the above example, 
				#include <stdio.h>
				char *hello_world(char *)
			are copied.
		2) Then bunch of #defines and variables which will be used by yacc
		   generated code comes.

		*3) Then user defined code will be copied.
		   In this above example, 
			char *
			print_str(char *s)
				return (s);
		4) Then tables generated by yacc comes in.
		5) Then finally the parser generated by yacc comes.
			This is yyparse() and in the example above,
			the generated parser will call print_str() and

	The spec says *3) part should be copied after 5).
		If *3) part is copied after yyparse(), then the C compiler later
		will complain that print_str() is implicitly declared as int type,
		but later it is redeclared as char *.

	So the spec says, that the functions that the parser uses should be
	declared at the declaration section.
		 * Declaration
		#include <stdio.h>
		char *hello_world(char *);
		char *print_str(char *);

	Quite many existing yacc input are written like ding.y expecting that
	print_str() does not need to be declared at the declaration section.
	(Because user codes are copied before yyparse().)

WG15 response for 9945-2:1993

First note that in B) the relevent section is A., not A.

The standard states behavior for the yacc code file, and conforming
implementations must conform to this.  However, concerns have been raised
about this which are being referred to the sponsor.

Forwarded to Interpretations group: 10 Jan 95
Response received: Feb 10 1995
Proposed Resoln forwarded: 13th Feb 1995
Finalised: March 28th 1995