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The latest version of ghc-typelits-knownnat is 0.7.12-0.

ghc-typelits-knownnat

Version 0.1.1 revision 0 uploaded by ChristiaanBaaij.

Package meta

Synopsis
Derive KnownNat constraints from other KnownNat constraints
Description

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.

Author
Christiaan Baaij
Bug reports
n/a
Category
Type System
Copyright
Copyright © 2016 University of Twente
Homepage
http://clash-lang.org/
Maintainer
christiaan.baaij@gmail.com
Package URL
n/a
Stability
n/a

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