Paquet : libghc-ghc-typelits-knownnat-doc (0.7.7-1)

Derive KnownNat constraints from other KnownNat constraints; documentation

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<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.

This package provides the documentation for a library for the Haskell programming language. See http://www.haskell.org/ for more information on Haskell.

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