typerep-map introduces TMap and TypeRepMap — data structures like Map, but where types serve as keys, and values have the types specified in the corresponding key spots.

For the more details on the implementation see the following blog post:

• typerep-map step by step

Usage example

ghci> import Data.TMap
ghci> tm = insert True $ one (42 :: Int)
ghci> size tm
2
ghci> res = lookup tm
ghci> res :: Maybe Int
Just 42
ghci> res :: Maybe Bool
Just True
ghci> res :: Maybe String
Nothing
ghci> lookup (insert "hello" tm) :: Maybe String
Just "hello"
ghci> member @Int tm
True
ghci> tm' = delete @Int tm
ghci> member @Int tm'
False

Benchmarks

Tables below contain comparision with DMap TypeRep of ten lookup operations on structure with size 10^4:

ghc-8.2.2	ghc-8.4.3