ghc-typelits-knownnat

Derive KnownNat constraints from other KnownNat constraints

http://clash-lang.org/

Version on this page:0.1.1
LTS Haskell 24.18:0.7.13
Stackage Nightly 2025-11-04:0.8.2
Latest on Hackage:0.8.2

See all snapshots ghc-typelits-knownnat appears in

BSD-2-Clause licensed by Christiaan Baaij
Maintained by [email protected]
This version can be pinned in stack with:ghc-typelits-knownnat-0.1.1@sha256:62d4ae6fc19ad3f691c0b612dff7375d00d8ab6139ca2f90f85807938d79f799,3236

Module documentation for 0.1.1

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 only derive KnownNat constraints consisting of:

  • Type-level naturals
  • Type variables
  • Applications of the arithmetic expression: {+,*,^}.

i.e. it cannot derive a KnownNat (n-1) constraint from a KnownNat n constraint

To use the plugin, add the

OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver

Pragma to the header of your file.

Changes

Changelog for the ghc-typelits-knownnat package

0.1.1 August 11th 2016

  • Fixes bug: panic on a non-given KnownNat constraint variable

0.1 August 10th 2016

  • Initial release