Re: Bottom-up versus Top-down (Torben AEgidius Mogensen)
12 Dec 1997 14:44:09 -0500

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Re: Bottom-up versus Top-down (1997-12-05)
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Re: Bottom-up versus Top-down (Henry Spencer) (1997-12-07)
Re: Bottom-up versus Top-down (1997-12-07)
Re: Bottom-up versus Top-down (Jeff Jenness) (1997-12-10)
Re: Bottom-up versus Top-down (Scott Stanchfield) (1997-12-10)
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From: (Torben AEgidius Mogensen)
Newsgroups: comp.compilers
Date: 12 Dec 1997 14:44:09 -0500
Organization: Department of Computer Science, U of Copenhagen
References: 97-11-123 97-11-155 97-11-178 97-12-024 97-12-055 97-12-073
Keywords: parse

"Scott Stanchfield" <> writes:

>For some info on converting grammar from LALR to LL, see


As I see it, a major advantage of LR over LL is the ability to use
operator precedence rules instead of using a non-ambiguous grammar.
Though precedence-annotated grammars can be rewritten to a
non-ambiguous grammar and left-recursion can be eliminated from this,
the size of the resulting grammar can be very large if you have both
prefix, infix and postfix operators. In addition to increasing the
size of the grammar, the disambiguating rewrites also slow down the
parsing by requiring more derivation steps.

That said, LR tables are often larger than LL tables, and the same is
true for explicitly written recursive descent/ascent. This doesn't
seem to be a problem until you get extremely large grammars, though.

Torben Mogensen (

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