Re: Bottom-up versus Top-down

Mark K. Gardner <mkgardne@cs.uiuc.edu> (or perhaps our moderator) wrote:
>[I did not witness the events first-hand, but it appears that LALR
>grew strength from languages, like C, that were difficult if not
>impossible to cast as LL grammars, while LL took root in the Pascal
>languages...


This is actually somewhat amusing, because the first C compiler in fact
used a top-down parser, and one of the early implementors of a bottom-up
C parser (Steve Johnson) complained in print that the language was designed
for top-down and was awkward to parse bottom-up!


Speaking as someone who has written a top-down parser for full ANSI C,
it's a little messy in spots, and there are a couple of places where you
need to cheat with a bit of extra lookahead, but it's neither impossible
nor immensely difficult. Annoying, yes, but entirely feasible.
--
| Henry Spencer
| henry@zoo.toronto.edu
[Hey, the Ritchie C compiler wasn't entirely top down. It did expressions
bottom up with a little operator precedence grammar. -John]




--

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