Re: advice needed re: parsing C decl syntax

> ... Doing [automatic error recovery] in a procedural recursive-descent
> parser requires passing recovery sets to each parsing procedure...
> This slows the parser (even when parsing a syntactically correct program),
> and increases the stack space requirements...


On the contrary, doing automatic error recovery in recursive descent does
not require this, although one particular error-recovery algorithm may.
(I would add that if you are implementing the usually-sparse recovery sets
as bitmaps and passing them by value, as one might all-too-easily do in
Pascal, it's not surprising that the result is slow and bulky.) Building
automatic error recovery into a recursive-descent parser is not difficult
or inefficient if you think hard and do it right; I speak from experience
with a C parser, not exactly a favorable case. While I tend to agree that
table-driven parsers are likely to be a lot smaller and possibly somewhat
faster, the *practical* differences in error recovery are not significant.


(Why was I doing recursive-descent parsing if I think table-driven is
better, you ask? Partly because of some of the nice practical conveniences
of recursive descent, partly because the particular project was supposed to
be highly portable and hence I didn't want to be dependent on a big parser
generator that I couldn't export freely. I tinkered with hand-generated
tables for a bit, and I think that approach could have been made to work
acceptably, but it was taking too long to get all the details right.)


Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,decvax,pyramid}!utzoo!henry

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