Re: Re. Is PASCAL LL/LR (Piet van Oostrum)
29 Oct 90 14:47:25 GMT

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Re. Is PASCAL LL/LR sankar@Neon.Stanford.EDU (1990-10-26)
Re: Re. Is PASCAL LL/LR (1990-10-29)
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Newsgroups: comp.compilers
From: (Piet van Oostrum)
In-Reply-To: sankar@Neon.Stanford.EDU (Sriram Sankar)
Keywords: Pascal, parse, LL(1)
Organization: Dept of Computer Science, Utrecht University, The Netherlands
References: <1990Oct26.213044.28243@Neon.Stanford.EDU>
Date: 29 Oct 90 14:47:25 GMT

>>>>> 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,
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: (*`Pete')

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