ccc-2019.hs

ccc-2019.hs

-- Compilation : ghc ccc2019.hs -o regex
-- Usage : ./regex "a*b" "aaab"

import System.Environment
import System.Exit
main :: IO ()

        

eq a b  | a == '.' = True 
        | otherwise = a == b
match (a:'*':xa) (b:xb) | eq a b = match (a:'*':xa) xb 
                        | otherwise = match xa (b:xb)

match (a:'*':xa) [] = match xa []

match (a:xa) (b:xb) | eq a b = match xa xb
                    | otherwise = False

match [] [] = True
match _ _   = False

-- Ext return code to be pipe-able on bash
exit True = exitWith ExitSuccess
exit False = exitWith (ExitFailure 1)

main = do 
        args <- getArgs
        let result = match (head args) (last args)
        print result
        exit result