On Fri, 11 May 2007, Malcolm Wallace wrote:
*Text.ParserCombinators.PolyLazy> runParser (exactly 4 (satisfy Char.isAlpha)) ("abc104"++undefined) ("*** Exception: Parse.satisfy: failed
This output is exactly correct. You asked for the first four characters provided that they were alphabetic, but in fact only the first three were alphabetic. Hence, 'satisfy' failed and threw an exception. If you ask for only the first three characters, then the parse succeeds:
The problem is obviously that a later wrong character can make the whole parse fail. Thus successful generated data is not returned until the whole input is parsed and checked. How can I suppress checking the whole input? How can I tell the parser that everything it parsed so far will not be invalidated by further input? How can I rewrite the above example that it returns ("abc*** Exception: Parse.satisfy: failed ? I wondered whether 'commit' helps, but it didn't. (I thought it would convert a global 'fail' to a local 'error'.) *Text.ParserCombinators.PolyLazy> runParser (exactly 4 (commit (satisfy Char.isAlpha))) ("abc104"++undefined) *** Exception: Parse.satisfy: failed