Re: PERFORM token (was RE: gnubol: Hacks needed to parse COBOL

[Michael McKernan <mck@tivoli.mv.com>]

>>>>> "Bill" == William M Klein <wmklein@ix.netcom.com>
>>>>> wrote the following on Thu, 2 Dec 1999 16:25:49 -0600

      <snip>

  >> I think that with a single look-ahead you can determine whether
  >> the word that follows the PERFORM is a reserved word such as
  >> UNTIL or VARYING, a verb, or a user defined word, that must be a
  >> procedure name.  Then you can either verify a previously
  >> tabulated name and issue errors, or tabulate the first-used name
  >> as a referenced procedure, and leave further error reporting to
  >> the semantic phase.
  >> 
  >> 

  Bill> The statement about a user-defined word following PERFORM
  Bill> being a procedure-name is not correct.

  Bill> Either Perform paragraph-name *> out-of-line PERFORM

  Bill>         or

  Bill>    Perform data-name TIMES *> in-line perform

  Bill> is valid


This is a good candidate for semantic classification of ref's but
bear in mind that a procedure ref, when it is a forward reference,
will not be available in the symbol table at the time it's needed.  A
lookup failure would have to be interpreted as a procedure name.

I am generally in favor of reference classification, but a purely
syntactic grammar for PERFORM is feasible with lookahead for one
case.  This is a pccts grammar with lookahead for "times_phrase".

perform_stmt
	: PERFORM
		(( times_phrase )?  times_phrase perform_body
		| { test_phrase }
			( UNTIL condition perform_body
			| ( varying_phrase )+ perform_body
			)
		| perform_body
		| procedure_ref
			{ times_phrase 
			| { test_phrase }
				( UNTIL condition
				| ( varying_phrase )+
				)
			}
		)
	;

times_phrase
	: ( INTEGER | identifier ) TIMES
	;

test_phrase
	: {WITH} TEST ( BEFORE | AFTER ) 
	;

varying_phrase
	: VARYING identifier 
	  FROM (identifier | INTEGER)
	  BY (identifier | INTEGER) 
	  UNTIL condition
	;

perform_body
	: ( statement )+ END_PERFORM
	;

	...

procedure_ref
	: PROC_NAME { OF_IN PROC_NAME }
	;







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