The type-level-sets package

[Tags:bsd3, library]

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.


Versions 0.5, 0.6, 0.6.1, 0.7,
Dependencies base (<5), ghc-prim [details]
License BSD3
Copyright 2013-16 University of Cambridge
Author Dominic Orchard
Maintainer Dominic Orchard
Category Type System, Data Structures
Source repository head: git clone
Uploaded Sun Sep 4 20:57:51 UTC 2016 by DominicOrchard
Distributions NixOS:
Downloads 821 total (45 in the last 30 days)
0 []
Status Docs available [build log]
Last success reported on 2016-09-04 [all 1 reports]
Hackage Matrix CI




Maintainer's Corner

For package maintainers and hackage trustees