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  1. {-# LANGUAGE MonadComprehensions #-}
  2. import Control.Applicative
  3.  
  4. foo x = ["0"| x == 0] 
  5.     <|> ["1"| x == 1] 
  6.     <|> ["bus number " ++ show x | x >= 100, x < 200] :: Maybe String
  7.  
  8. main = mapM_ print $ [foo 0, foo 1, foo 50, foo 150, foo 300]
Success #stdin #stdout 0s 5692KB
comments (?)
stdin
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Standard input is empty
stdout
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Just "0"
Just "1"
Nothing
Just "bus number 150"
Nothing
https://ideone.com/1acYMl
language:
Haskell (ghc 8.4.4)
created:
11 years ago
visibility:
public

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