if-instance: Branch on whether a constraint is satisfied
This library provides a mechanism that can be used to branch on whether a constraint is satisfied (not limited to typeclass instances).
Usage example:
{-# OPTIONS_GHC -fplugin=IfSat.Plugin #-} module MyModule where import Data.Constraint.If ( IfSat(ifSat) ) hypot :: forall a. ( Floating a, IfSat (FMA a) ) => a -> a -> a hypot = ifSat @(FMA a) withFMA withoutFMA where withFMA :: FMA a => a -> a -> a withFMA x y = let h = sqrt $ fma x x (y * y) h² = h * h x² = x * x u = fma (-y) y (h² - x²) + fma h h (-h²) - fma x x (-x²) in h - u / ( 2 * h ) withoutFMA :: a -> a -> a withoutFMA x y = sqrt ( x * x + y * y )
Here we select between two ways of computing the hypotenuse function based on whether we have access to the fused multiply-add operation
fma :: FMA a => a -> a -> a -> a
which computes \ x y z -> ( x * y ) + z
in a single instruction,
providing stronger guarantees about precision of the result.
A call of the form hypot @MyNumberType
will either use the robust withFMA
function when an FMA MyNumberType
instance is available, or will fallback
to the simple withoutFMA
implementation when no such instance can be found.
library if-instance
library if-instance:if-instance-example
Downloads
- if-instance-0.5.2.0.tar.gz [browse] (Cabal source package)
- Package description (as included in the package)
Maintainer's Corner
For package maintainers and hackage trustees
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Versions [RSS] | 0.1.0.0, 0.2.0.0, 0.2.1.0, 0.2.1.1, 0.3.0.0, 0.3.1.0, 0.4.0.0, 0.5.0.0, 0.5.1.0, 0.5.2.0 (info) |
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Change log | changelog.md |
Dependencies | base (>=4.15.0 && <4.22), ghc (>=9.0 && <9.14), ghc-tcplugin-api (>=0.13 && <0.15), if-instance [details] |
License | BSD-3-Clause |
Copyright | 2021 Sam Derbyshire |
Author | Sam Derbyshire |
Maintainer | Sam Derbyshire |
Category | Type System, Plugin |
Home page | https://github.com/sheaf/if-instance |
Uploaded | by sheaf at 2024-11-29T12:37:47Z |
Distributions | |
Downloads | 765 total (39 in the last 30 days) |
Rating | (no votes yet) [estimated by Bayesian average] |
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Status | Docs available [build log] Last success reported on 2024-11-29 [all 1 reports] |