On 3 Aug 2013, at 21:03, Jason Dagit wrote:
> Another con of using parsec that I forgot to mention in my previous
> email is that with Parsec you need to be explicit about backtracking
> (use of try). Reasoning about the correct places to put try is not
> always easy and parsec doesn't help you with the task. In my
> experience, this is the main bug that people run into when using
> parsec.
Although the original question did not mention parsec explicitly, I find it
disappointing that many people immediately think of it as the epitome of
monadic combinator parsing. The power of good marketing, eh? There are so
many other good parsing libraries out there. Parsec happened to cure some
known space-leaks in rival libraries about the time of its release (2000 or
so), but the main reason it is popular is simply because it was distributed
alongside ghc for a long time.
Curiously enough, the complaint you make about parsec is exactly the same as
the observation that drove the development of my own set of combinators -
polyparse. But the concept of commitment to a partial parse (to prevent
backtracking) was already present somewhat in Röjemo's applicative parsers way
back in 1994. He had both `ap` and `apCut` (the naming of "cut" borrowed from
Prolog I suppose). Space performance and the elimination of space leaks was
totally his focus: he mentions being able to recompile the compiler itself in
just 3Mb of RAM.
Regards,
Malcolm
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