libghc-ghc-typelits-knownnat-dev - 0.7.12-1+b1 main

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:
.
* Type variables, when there is a corresponding KnownNat constraint
.
* Type-level naturals
.
* Applications of the arithmetic expression: +,-,*,^
.
* Type functions, when there is either:
.
1. a matching given KnownNat constraint; or
.
2. a corresponding KnownNat 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.
.
This package provides a library for the Haskell programming language.
See http://www.haskell.org/ for more information on Haskell.