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From: piet@cs.ruu.nl (Piet van Oostrum)
Newsgroups: comp.compilers
Subject: Re: Re. Is PASCAL LL/LR
Keywords: Pascal, parse, LL(1)
Message-ID: <4134@ruuinf.cs.ruu.nl>
Date: 29 Oct 90 14:47:25 GMT
References: <1990Oct26.213044.28243@Neon.Stanford.EDU>
Sender: compilers-sender@iecc.cambridge.ma.us
Reply-To: piet@cs.ruu.nl (Piet van Oostrum)
Organization: Dept of Computer Science, Utrecht University, The Netherlands
Lines: 25
Approved: compilers@esegue.segue.boston.ma.us
In-Reply-To: sankar@Neon.Stanford.EDU (Sriram Sankar)

>>>>> In article <1990Oct26.213044.28243@Neon.Stanford.EDU>, sankar@Neon.Stanford.EDU (Sriram Sankar) (SS) writes:

SS>   Since PASCAL has a rule that dangling else's associate with the
SS> innermost 'if', it seems obvious to me that PASCAL (at least wrt to the
SS> if statement) is LR.  If the dangling else was associated with the
SS> outermost 'if' you can still make the necessary S/R decisions, so I do
SS> think (not looked at it carefully enough though) that this too is LR.

It is even very easy to rewrite the grammar to be LR(1). Someone did that a
few postings ago. See also the dragon book [1], p. 175

The dragon book also states that it is impossible to change the
if-then-else grammar to an equivalent one that is LL(1) (page 192). I have
not seen a proof of this, so I accept this by faith.

[1] Aho, Sethi and Ullman, Compilers, Principles, Techniques and Tools,
Addison-Wesley.
-- 
Piet* van Oostrum, Dept of Computer Science, Utrecht University,
Padualaan 14, P.O. Box 80.089, 3508 TB Utrecht, The Netherlands.
Telephone: +31 30 531806   Uucp:   uunet!mcsun!ruuinf!piet
Telefax:   +31 30 513791   Internet:  piet@cs.ruu.nl   (*`Pete')
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