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  1. {-# LANGUAGE FlexibleInstances, TypeFamilies, IncoherentInstances #-}
  2.  
  3. class Foo a where
  4.    foo :: a
  5.  
  6. instance a ~ Int => Foo (String -> a) where
  7.    foo = length
  8.  
  9. instance a ~ String => Foo a where
  10.    foo = "world"
  11.  
  12. main = do
  13.   print $ foo "hello"
  14.   print $ foo
Success #stdin #stdout 0s 4592KB
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Standard input is empty
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5
"world"
https://ideone.com/MrJjMi
language:
Haskell (ghc 8.4.4)
created:
10 years ago
visibility:
public

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