[antlr-interest] left recursion removal

[Jim Idle]

With the example this time:


ifStatement
	: IF e=expression
		(
			  t=THEN
			  	(
			  	  		// Single line IF
statement as the last token was not a NL
			  	  		//
			  	  		s1=statements
((ELSE)=>ELSE s2=statements)?

						-> {$s2.tree == null}?
^(IFLINE $e ^(THEN $s1))
						->
^(IFLINE $e ^(THEN $s1) ^(ELSE $s2*))

			  	  | (NL|COLON)+

			  	  	// We discovered a NL token, hence
we process
			  	    // a block If here as it has to be a
block when the line with
			  	    // the IF on it has a NL before the
first statement.
			  	    //
			  	    ib=ifBlock

			  	    	-> ^(IF $e $ib)
			  	)

			| (NL|COLON)+

			  // We did not see a THEN clause, but it is
optional on block IF statements
			  // (which is a bit silly, but a left over from
VB 1 I suspect. Hence we process
			  // a block If here.
			  //
			  ib=ifBlock

			  		-> ^(IF $e $ib)
		)
	;

ifBlock
	: 		tb=block

	  		(eib+=elseIfStatement)*

	 		(
	 			  ec=elseClause		// Else Clause
handles END IF
				| END IF
			)

		->	^(THEN $tb?) $eib* $ec?
	;

elseClause
	: 	ELSE^ 	(
					  (NL!|COLON!)+ block END! IF!
					| statement
				)
	;


elseIfStatement
	: ELSEIF e=expression THEN? (NL|COLON)+ b=block

		-> ^(ELSEIF $e $b?)
	;

Where 'block' is one or more statements (might need zero or more for
powerbuilder).

Jim

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Sébastien Kirche
> Sent: Wednesday, July 06, 2011 4:28 PM
> To: John B. Brodie
> Cc: antlr-interest
> Subject: Re: [antlr-interest] left recursion removal
>
> Le 7 juillet 2011 00:14, John B. Brodie <jbb at acm.org> a écrit :
> > Greetings!
> >
> > [...]
> >
> > unable to reproduce.
> >
> > given your admittedly partial grammar, i tried to construct a
> complete
> > example by adding the missing elements and creating an AST (so i
> could
> > know the resultant parse).
> >
> > my test rig is attached.
> >
> > it runs without error when Tool'd, compiled, and executed from the
> > command-line (FWIW i use Ubunto 11.04 Linux running Sun Java 6 and
> the
> > Antlr version from the antlr-3.4-complete.jar file).
> >
> > Please try to post the *smallest* yet *complete* example of your
> > problem.
>
> Sorry for not having posted a more complete code before, I though that
> should have been enough...
>
> I have worked further on my grammar, with trying to define more
> precisely what an expression should be, with operator precedence. This
> made me rewrite the singleStatement by moving the funCall  rule to the
> primary rule. But my problem about the if-then-else construct is not
> gone.
>
> I have stripped down my grammar, keeping only the expression and
> subsequent rules, removed all that define loops, switches, etc.
> Given that simplified grammar, the following script should pass the
> parsing, but it can't yet :
>
> ---------------------------------------
> string s1, s2
>
> if s1='42' then s2='421'
>
> if s2='421' then
> 	string s3
> 	s3='123'
> else
> 	string s4
> 	s4='666'
> end if
>
> ---------------------------------------
>
> Also, to Jim Idle : the language I would be able to parse is
> Powerbuilder. You can see it as a sort of basic, while it accepts
> syntax like i++ or s += 'foo' He has also the ability to accept inline
> sql statements... I tried to play on the EndOfLine delimiter to handle
> the two if-then-else syntaxes but without success.
>
> --
> Sébastien Kirche