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  1. {-# LANGUAGE FlexibleInstances #-}
  2. {-# LANGUAGE OverlappingInstances #-}
  3.  
  4. class IsList a where
  5.   isList :: a -> Bool
  6.  
  7. instance IsList a where
  8.   isList x = False
  9.  
  10. instance IsList [a] where
  11.   isList x = True
  12.  
  13. isList2 :: (IsList a) => a -> Bool
  14. isList2 = isList
  15.  
  16. main = do
  17.   print (isList (42 :: Int))
  18.   print (isList [42 :: Int])
  19.   print (isList2 (42 :: Int))
  20.   print (isList2 [42 :: Int])
  21.  
Success #stdin #stdout 0s 5720KB
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stdin
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Standard input is empty
stdout
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False
True
False
True
https://ideone.com/rLbJiH
language:
Haskell (ghc 8.4.4)
created:
11 years ago
visibility:
secret

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