Difference between revisions of "Implicit parameters"

Latest revision as of 22:55, 12 June 2021

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]))

@@ Line 1: / Line 1: @@
+{{GHCUsersGuide|exts/implicit_parameters||an Implicit Parameters section}}
-The GHC manual on implicit parameters: [https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#implicit-parameters].
 Working example:
@@ Line 7: / Line 7: @@
  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]]