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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:

Usage example🔗

ghci> import Data.TMap

ghci> tm = insert True $ one (42 :: Int)

ghci> size tm

ghci> res = lookup tm

ghci> res :: Maybe Int
Just 42

ghci> res :: Maybe Bool
Just True

ghci> res :: Maybe String

ghci> lookup (insert "hello" tm) :: Maybe String
Just "hello"

ghci> member @Int tm

ghci> tm' = delete @Int tm

ghci> member @Int tm'


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 ghc-8.8.3 ghc-8.10.1
DMap TypeRep 517.5 ns 779.9 ns 1.559 μs 1.786 μs
typerep-map 205.3 ns 187.2 ns 190.1 ns 169.1 ns
ghc-8.2.2 ghc-8.4.3
DMap 8.2.2 DMap 8.4.3
TMap 8.2.2 TMap 8.4.3