The type-level-sets package


This package provides type-level sets (no duplicates, sorted to provide a normal form) via 'Set' and type-level finite maps via 'Map', with value-level counterparts.

Described in the paper "Embedding effect systems in Haskell" by Dominic Orchard and Tomas Petricek <> (Haskell Symposium, 2014). This version now uses Quicksort to normalise the representation.

Here is a brief example for finite maps:

@ import Data.Type.Map

type instance Combine Int Int = Int instance Combinable Int Int where combine x y = x + y

foo :: Map '["x" :-> Int, "z" :-> Bool, "w" :-> Int] foo = Ext (Var :: (Var "x")) 2 $ Ext (Var :: (Var "z")) True $ Ext (Var :: (Var "w")) 5 $ Empty

bar :: Map '["y" :-> Int, "w" :-> Int] bar = Ext (Var :: (Var "y")) 3 $ Ext (Var :: (Var "w")) 1 $ Empty

foobar = foo `union` bar


The 'Map' type for 'foobar' here shows the normalised form (sorted with no duplicates). The type signatures is commented out as it can be infered. Running the example we get:

@ > >>> foobar > w :-> 6, x :-> 2, y :-> 3, z :-> True @

Thus, we see that the values for \"w\" are added together.

For sets, here is an example:

@ import GHC.TypeLits import Data.Type.Set type instance Cmp (Natural n) (Natural m) = CmpNat n m

data Natural (a :: Nat) where Z :: Natural 0 S :: Natural n -> Natural (n + 1)

foo = asSet $ Ext (S Z) (Ext (S (S (S Z))) (Ext Z Empty))

bar = asSet $ Ext (S (S Z)) (Ext (S Z) (Ext (S Z) Empty))

foobar = foo `union` bar

@ Note the types here are all inferred.


Versions0.5, 0.6, 0.6.1, 0.7,,
Dependenciesbase (<5), ghc-prim [details]
Copyright2013-16 University of Cambridge
AuthorDominic Orchard
MaintainerDominic Orchard
CategoryType System, Data Structures
Source repositoryhead: git clone
UploadedSun Sep 4 20:46:02 UTC 2016 by DominicOrchard




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