ghc-typelits-knownnat

Version 0.1 revision 0 uploaded 2016-08-10T17:41:44.000Z 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

Components

• lib:ghc-typelits-knownnat
• test:test-ghc-typelits-knownat