On Thu, Feb 16, 2006 at 11:28:08PM +0000, Malcolm Wallace wrote:
Essentially, rather than having an indication of success/failure in the type system, using the Maybe or Either types, you are asking to return the typed value itself, with no wrapper, but perhaps some hidden bottoms buried inside. One could certainly define such a parsing set-up, but there are no standard ones I know of. The attraction of lazy parsing is obvious, but there is a cost in terms of safety.
Yeah, I have thought about the best way to do this before, something like all combinators by default being irrefutable meaning they always succeed perhaps placing bottoms in the structure, with a specific 'try' like in parsec that will let you try a path and backtrack locally. I was thinking something like a continuation based error monad where the error continuation was 'bottom' unless overridden locally, but I never could get the types to work out quite right. perhaps rank-n types or following the process outlined in the parallel parsing combinators paper will afford a better result. John -- John Meacham - ⑆repetae.net⑆john⑈