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-- Check that pattern match failure in do-notation
-- is reflected by calling the monadic 'fail', not by a
-- runtime exception
{-# LANGUAGE NoMonadFailDesugaring #-}
import Control.Monad
import Data.Maybe
test :: (MonadPlus m) => [a] -> m Bool
test xs
= do
(_:_) <- return xs
-- Should fail here
return True
`mplus`
-- Failure in LH arg should trigger RH arg
do
return False
main :: IO ()
main
= do let x = fromJust (test [])
putStrLn (show x)
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