Difference between revisions of "Implicit parameters"

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{{GHCUsersGuide|exts/implicit_parameters||an Implicit Parameters section}}
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The GHC manual on implicit parameters: [http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#implicit-parameters].
  
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Working example:
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{-# LANGUAGE ImplicitParams #-}
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import Data.List (sortBy)
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sortBy' :: (?cmp :: a -> a -> Ordering) => [a] -> [a]
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sortBy' = sortBy ?cmp
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sort :: Ord a => [a] -> [a]
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sort = let ?cmp = compare in sortBy'
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main = putStrLn (show (sort [3,1,2]))
   
 
[[Category:Language extensions]]
  
[[Category:Language extensions]]

Latest revision as of 22:55, 12 June 2021

The GHC Users Guide has an Implicit Parameters section.

Working example: 

{-# LANGUAGE ImplicitParams #-}

import Data.List (sortBy)

sortBy' :: (?cmp :: a -> a -> Ordering) => [a] -> [a]
sortBy' = sortBy ?cmp

sort :: Ord a => [a] -> [a]
sort = let ?cmp = compare in sortBy'

main = putStrLn (show (sort [3,1,2]))
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