The type-level-sets package

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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,,,,,
Change logNone available
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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