|LL1 grammar conversion Algorithms email@example.com (1997-02-11)|
|Re: LL1 grammar conversion Algorithms firstname.lastname@example.org (John Lilley) (1997-02-16)|
|Re: LL1 grammar conversion Algorithms email@example.com (Scott Stanchfield) (1997-02-16)|
|From:||John Lilley <firstname.lastname@example.org>|
|Date:||16 Feb 1997 22:25:10 -0500|
|Organization:||Nerds for Hire, Inc.|
> Does anyone know of any implementation of an algorithm which will
> convert an LALR grammar to LL1.
> Particularly elimination of common prefix and left recursion ( as in
> Fischer and LeBlanc's "Crafting a Compiler in C )
> [It's not possible in general...
I should also add that LALR grammars that were automatically converted
to LL can be totally unreadable. Some of the issues are:
1) LL grammar tools like PCCTS have repition constructs like ()* and
()+ which remove much recursion found in LALR grammars. An automatic
tool will probably ignore that feature.
2) It is often better to backtrack in an LL grammar than to
left-factor for particularly awful cases. The automatic tool may find
that the common prefix is quite long and generate a perfectly awful
and grotesquely verbose LL grammar as a result.
3) There are some differences between actions embedded in an LL
grammar and those in an LR grammar, so the automatic conversion may
make incorrect action placement.
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