dependent-map

This library defines a dependently-typed finite map type. It is derived from Data.Map.Map in the containers package, but rather than (conceptually) storing pairs indexed by the first component, it stores DSums (from the dependent-sum package) indexed by tag. For example

{-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE TypeFamilies #-} module Example where import Data.Constraint.Extras.TH (deriveArgDict) import Data.Dependent.Map (DMap, fromList, singleton, union, unionWithKey) import Data.Dependent.Sum ((==>)) import Data.Functor.Identity (Identity(..)) import Data.GADT.Compare.TH (deriveGCompare, deriveGEq) import Data.GADT.Show.TH (deriveGShow) data Tag a where StringKey :: Tag String IntKey :: Tag Int DoubleKey :: Tag Double deriveGEq ''Tag deriveGCompare ''Tag deriveGShow ''Tag deriveArgDict ''Tag x :: DMap Tag Identity x = fromList [DoubleKey ==> pi, StringKey ==> "hello there"] y :: DMap Tag Identity y = singleton IntKey (Identity 42) z :: DMap Tag Identity z = y `union` fromList [DoubleKey ==> -1.1415926535897931] addFoo :: Tag v -> Identity v -> Identity v -> Identity v addFoo IntKey (Identity x) (Identity y) = Identity $ x + y addFoo DoubleKey (Identity x) (Identity y) = Identity $ x + y addFoo _ x _ = x main :: IO () main = mapM_ print [ x, y, z , unionWithKey addFoo x z ]