ghc-typelits-knownnat: Derive KnownNat constraints from other KnownNat constraints

This is a package candidate release! Here you can preview how this package release will appear once published to the main package index (which can be accomplished via the 'maintain' link below). Please note that once a package has been published to the main package index it cannot be undone! Please consult the package uploading documentation for more information.

[maintain] [Publish]

Warnings:

A type checker plugin for GHC that can derive "complex" KnownNat constraints from other simple/variable KnownNat constraints. i.e. without this plugin, you must have both a KnownNat n and a KnownNat (n+2) constraint in the type signature of the following function:

f :: forall n . (KnownNat n, KnownNat (n+2)) => Proxy n -> Integer
f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))

Using the plugin you can omit the KnownNat (n+2) constraint:

f :: forall n . KnownNat n => Proxy n -> Integer
f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))

The plugin can derive KnownNat constraints for types consisting of:

  1. a matching given KnownNat constraint; or

  2. a corresponding KnownNat<N> instance for the type function

To use the plugin, add the

OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver

Pragma to the header of your file.


[Skip to Readme]

Properties

Versions 0.1, 0.1.1, 0.2, 0.2.1, 0.2.2, 0.2.3, 0.2.4, 0.3, 0.3.1, 0.4, 0.4.1, 0.4.2, 0.5, 0.5.1, 0.6, 0.7, 0.7.1, 0.7.2, 0.7.3, 0.7.4, 0.7.5, 0.7.5, 0.7.6
Change log CHANGELOG.md
Dependencies base (>=4.9 && <5), ghc (>=8.0.1 && <9.2), ghc-prim (>=0.4.0.0 && <0.8), ghc-tcplugins-extra (>=0.3.1), ghc-typelits-natnormalise (>=0.7.1 && <0.8), integer-gmp (>=0.5.1.0), template-haskell (>=2.11.0.0 && <2.18), transformers (>=0.5.2.0 && <0.6) [details]
License BSD-2-Clause
Copyright Copyright © 2016 , University of Twente, 2017-2018, QBayLogic B.V., 2017 , Google Inc.
Author Christiaan Baaij
Maintainer christiaan.baaij@gmail.com
Category Type System
Home page http://clash-lang.org/
Source repo head: git clone https://github.com/clash-lang/ghc-typelits-knownnat.git
Uploaded by ChristiaanBaaij at 2021-02-10T10:04:57Z

Modules

[Index]

Manual Flags

NameDescriptionDefault
deverror

Enables `-Werror` for development mode and TravisCI

Disabled
Automatic Flags
NameDescriptionDefault

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info

Downloads

Maintainer's Corner

For package maintainers and hackage trustees


Readme for ghc-typelits-knownnat-0.7.5

[back to package description]

ghc-typelits-knownnat

Build Status Hackage Hackage Dependencies

A type checker plugin for GHC that can derive "complex" KnownNat constraints from other simple/variable KnownNat constraints. i.e. without this plugin, you must have both a KnownNat n and a KnownNat (n+2) constraint in the type signature of the following function:

f :: forall n . (KnownNat n, KnownNat (n+2)) => Proxy n -> Integer
f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))

Using the plugin you can omit the KnownNat (n+2) constraint:

f :: forall n . KnownNat n => Proxy n -> Integer
f _ = natVal (Proxy :: Proxy n) + natVal (Proxy :: Proxy (n+2))

The plugin can derive KnownNat constraints for types consisting of:

To elaborate the latter points, given the type family Min:

type family Min (a :: Nat) (b :: Nat) :: Nat where
  Min 0 b = 0
  Min a b = If (a <=? b) a b

the plugin can derive a KnownNat (Min x y + 1) constraint given only a KnownNat (Min x y) constraint:

g :: forall x y . (KnownNat (Min x y)) => Proxy x -> Proxy y -> Integer
g _ _ = natVal (Proxy :: Proxy (Min x y + 1))

And, given the type family Max:

type family Max (a :: Nat) (b :: Nat) :: Nat where
  Max 0 b = b
  Max a b = If (a <=? b) b a

and corresponding KnownNat2 instance:

instance (KnownNat a, KnownNat b) => KnownNat2 "TestFunctions.Max" a b where
  natSing2 = let x = natVal (Proxy @a)
                 y = natVal (Proxy @b)
                 z = max x y
             in  SNatKn z
  {-# INLINE natSing2 #-}

the plugin can derive a KnownNat (Max x y + 1) constraint given only a KnownNat x and KnownNat y constraint:

h :: forall x y . (KnownNat x, KnownNat y) => Proxy x -> Proxy y -> Integer
h _ _ = natVal (Proxy :: Proxy (Max x y + 1))

To use the plugin, add the

OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver

Pragma to the header of your file.