Parsers are easy to write (was: Re: Backtracking yacc)

andrewd@cs.adelaide.edu.au (Andrew Dunstan) writes:
>There are other reasons - LL parsers are easy to hand craft, making them
>good for teaching purposes (yes, I know we all use calculators, but we
>also have to know how to do arithmetic without them.) They can also be
>very fast.


All deterministic Context Free Grammars (and many of the non-deterministic
ones too) are easy to craft by hand.


In fact, I challenge anyone to find me one that I cannot craft a parser
for by hand in a short time ("short" meaning: less time than it takes to
write and debug an equivalent YACC source). Something like C is okay,
though it's not deterministic. But C's syntax is too easy, the operative
word here is Challenge.


Any takers?
[Don't forget to make sure that your hand-written parser diagnoses all invalid
input, as a yacc parser does. My experience is that the biggest wins from
using yacc are the automatic diagnosis of ambiguous grammars and the extreme
ease of adding little tweaks later on. -John]
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