Created
March 22, 2019 21:55
-
-
Save i-am-tom/d7ca4ebcb212cfb39d24e4b415d4614b to your computer and use it in GitHub Desktop.
Apply your function parameters in any order, for no reason other than that you can.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
{-# lAnGuAgE DataKinds #-} | |
{-# LaNgUaGe FlexibleInstances #-} | |
{-# lAnGuAgE FunctionalDependencies #-} | |
{-# LaNgUaGe KindSignatures #-} | |
{-# lAnGuAgE TypeFamilies #-} | |
{-# LaNgUaGe TypeOperators #-} | |
{-# lAnGuAgE UndecidableInstances #-} | |
module Commit where | |
import Data.Kind (Constraint, Type) | |
import GHC.TypeLits (TypeError, ErrorMessage (..)) | |
class Commit (f :: Type) (x :: Type) (g :: Type) | |
| f x -> g where | |
commit_ :: f -> x -> g | |
instance Commit (x -> k) x k where | |
commit_ = ($) | |
instance {-# iNcOhErEnT #-} Commit f x g | |
=> Commit (k -> f) x (k -> g) where | |
commit_ f x = \k -> commit_ (f k) x | |
type family (f :: Type) `Contains` (x :: Type) :: Constraint where | |
(x -> _) `Contains` x = () | |
(_ -> k) `Contains` x = k `Contains` x | |
_ `Contains` x = TypeError ('Text "This isn't one of my arguments!") | |
($$) :: (f `Contains` x, Commit f x g) => f -> x -> g | |
($$) = commit_ | |
infix 0 $$ | |
good :: (String -> Int -> Bool) -> (String -> Bool) | |
good f = f $$ (3 :: Int) | |
-- • This isn't one of my arguments! | |
-- • In the expression: f $$ [True] | |
-- In an equation for 'bad': bad f = f $$ [True] | |
-- bad :: (String -> Int -> Bool) -> _ | |
-- bad f = f $$ [True] |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment