git.iko.soy/typerep-map
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typerep-map/src/Data/TypeRep/Map.hs
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1{-# LANGUAGE ExplicitForAll #-}
2{-# LANGUAGE ScopedTypeVariables #-}
4module Data.TypeRep.Map
5 ( TypeRepMap (..)
6 , empty
7 , insert
8 , lookup
9 , size
10 , dbgShowTree
11 ) where
13import Prelude hiding (lookup)
15import Data.Proxy (Proxy (..))
16import Data.Typeable (TypeRep, Typeable, typeOf, typeRep)
17import GHC.Base (Any)
18import Unsafe.Coerce (unsafeCoerce)
20import qualified Data.Map.Lazy as LMap
22-- | Map-like data structure with types served as the keys.
23newtype TypeRepMap = TypeRepMap
24 { unMap :: LMap.Map TypeRep Any
25 }
27-- | Empty structure.
28empty :: TypeRepMap
29empty = TypeRepMap mempty
31-- | Inserts the value with its type as a key.
32insert :: Typeable a => a -> TypeRepMap -> TypeRepMap
33insert val = TypeRepMap . LMap.insert (typeOf val) (unsafeCoerce val) . unMap
35-- | Looks up the value at the type.
36-- >>> let x = lookup $ insert (11 :: Int) empty
37-- >>> x :: Maybe Int
38-- Just 11
39-- >>> x :: Maybe ()
40-- Nothing
41lookup :: forall a . Typeable a => TypeRepMap -> Maybe a
42lookup = fmap unsafeCoerce . LMap.lookup (typeRep (Proxy :: Proxy a)) . unMap
44size :: TypeRepMap -> Int
45size = LMap.size . unMap
47dbgShowTree :: TypeRepMap -> String
48dbgShowTree = LMap.showTreeWith (\k _ -> show k) False True . unMap