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:
a matching given 'KnownNat' constraint; or
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.
| Package Version | Update ID | Released | Package Hub Version | Platforms | Subpackages |
|---|---|---|---|---|---|
| 0.3-bp150.1.3 info | GA Release | 2018-07-30 | 15 |
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