On Fri, 2008-07-04 at 13:31 -0700, Badea Daniel wrote:
I'm trying to parse a large file looking for instructions on each line and for a section end marker but Parsec's manyTill function causes stack overflow, as you can see in the following example (I'm using ghci 6.8.3):
parse (many anyChar) "" ['a'|x<-[1..1024*64]]
It almost immediately starts printing "aaaaaaaaaaa...." and runs to completion.
parse (manyTill anyChar eof) "" ['a'|x<-[1..1024*1024]] *** Exception: stack overflow
I guess this happens because manyTill recursively accumulates output from the first parser and returns only when it hits the 'end' parser. Is it possible to write a version of 'manyTill' that works like 'many' returning output from 'anyChar' as soon as it advances through the list of tokens?
No, manyTill doesn't know whether it is going to return anything at all until its second argument succeeds. I can make manyTill not stack overflow, but it will never immediately start returning results. For the particular case above you can use getInput and setInput to get a result that does what you want. parseRest = do rest <- getInput setInput [] return rest That should probably update the position as well though it's not so crucial in the likely use-cases of such a function.