At 04:17 21/10/03 -0400, ajb@spamcop.net wrote:
I think I might have mentioned this previously, but here's an interesting implementation of Knuth-Morris-Pratt substring searching (which is indeed a "little language") which illustrates something or other:
Nice. Do you know if anyone has done anything like this for regular expressions? I'm thinking in particular that a function that turned a regular expression into a Parsec parser function could be useful, as in: regexp.compile :: String -> GenParser Char st [String] where GenParser is defined by the Parsec library [1], and the parsed result is a list of substrings corresponding to the (...) parts of the regexp (if matched, of course). (The parser result type might warrant some refinement.) #g -- [1] http://www.cs.uu.nl/~daan/parsec.html ParsecPrim.hs defines GenParser thus: [[ ----------------------------------------------------------- -- Parser definition. -- GenParser tok st a: -- General parser for tokens of type "tok", -- a user state "st" and a result type "a" ----------------------------------------------------------- type Parser a = GenParser Char () a newtype GenParser tok st a = Parser (State tok st -> Consumed (Reply tok st a)) runP (Parser p) = p data Consumed a = Consumed a --input is consumed | Empty !a --no input is consumed data Reply tok st a = Ok !a !(State tok st) ParseError --parsing succeeded with "a" | Error ParseError --parsing failed data State tok st = State { stateInput :: ![tok] , statePos :: !SourcePos , stateUser :: !st } ]] ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact