Failure should be our teacher, not our undertaker. Failure is delay, not defeat. It is a temporary detour, not a dead end. Failure is something we can avoid only by saying nothing, doing nothing, and being nothing.
Denis Waitley
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleConstraints #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# OPTIONS_GHC -fplugin=Data.Constraint.Emerge.Plugin #-}
module Test where
import Data.Constraint.Emerge
showAnything :: forall c. Emerge (Show c) => c -> String
showAnything c =
case emerge @(Show c) of
Just Dict -> show c
Nothing -> "<<unshowable>>"
showBool = showAnything True -- "True"
showId = showAnything id -- "<<unshowable>>"constraints-emergewill generate type-equality dictionaries any types (even ones that aren't equal 😱 😱 😱)- It fails to provide
Emerge cdictionaries at runtime. - The generated error messages mention mangled type variables; it would be cool if they didn't.
If someone wants to pick it up from here, that’d be great!
Please reports bugs and missing features at the GitHub bugtracker. This is also where you can find the source code.
constraints-emerge was written by Sandy Maguire and is licensed under a
permissive MIT license.