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{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE RoleAnnotations #-}
unit user where
signature Map where
type role Map nominal representational
data Map k a
class Key k
instance Key String
empty :: Map k a
lookup :: Key k => k -> Map k a -> Maybe a
insert :: Key k => k -> a -> Map k a -> Map k a
module User where
import Prelude hiding (lookup)
import Map
x = lookup "foo" (insert "foo" True empty)
unit ordmap where
module Map(module Data.Map, Key) where
import Data.Map
type Key = Ord
unit eqmap where
module Map where
import Prelude hiding (lookup)
import qualified Prelude
type role Map nominal representational
newtype Map k a = Assoc [(k, a)]
type Key = Eq
-- Ugh, need the type signatures, otherwise the quantifiers
-- are put in the wrong order. See #12441
empty :: Map k a
empty = Assoc []
lookup :: Eq k => k -> Map k a -> Maybe a
lookup k (Assoc xs) = Prelude.lookup k xs
-- Need to insert redundant constraint to make it work...
insert :: Eq k => k -> a -> Map k a -> Map k a
insert k v (Assoc xs) = Assoc ((k,v):xs)
unit main where
dependency user[Map=ordmap:Map] (User as User.Ord)
dependency user[Map=eqmap:Map] (User as User.Eq)
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