Difference between revisions of "Implicit parameters"

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m (Fix link to GHC doc)
Line 7: Line 7:
 
import Data.List (sortBy)
 
import Data.List (sortBy)
 
 
sort :: (?cmp :: a -> a -> Ordering) => [a] -> [a]
+
sortBy' :: (?cmp :: a -> a -> Ordering) => [a] -> [a]
sort = sortBy ?cmp
+
sortBy' = sortBy ?cmp
  +
  +
sort :: Ord a => [a] -> [a]
  +
sort = let ?cmp = compare in sortBy'
 
 
main = let ?cmp = compare in putStrLn (show (sort [3,1,2]))
+
main = putStrLn (show (sort [3,1,2]))
   
 
[[Category:Language extensions]]
 
[[Category:Language extensions]]

Revision as of 14:19, 9 July 2016

The GHC manual on implicit parameters: [1].

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]))