Use this tag for asking question related to Constraint Kind or/and ConstraintKinds GHC extension.
ConstraintKinds is an GHC Haskell extension. Also it is a type of kind.
Interesting Questions:
Questions tagged [constraint-kinds]
36 questions
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Conversion of distributive type families of constraints
Hypothesis: Type families which result in Constraints are always distributive over their representational parameters.
As an example, Fam x Eq `And` Fam x Show is equivalent to Fam x (Eq `And` Show) if Fam's second parameter has a representational…
yairchu
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Reducing satisfied constraints to ordinary types
I understand the following type family shouldn't and perhaps can't be implemented in GHC:
type family MatchesConstraint c a :: Bool where
MatchesConstraint c a is True if (c a)
MatchesConstraint c a is False otherwise
This is problematic…
Clinton
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How to abstract constraints in function with Rank-2 type?
The following snippet of code borrows from the Haskell wiki to carry around a typeclass dictionary along with an existential type:
{-# language ExistentialQuantification #-}
module Experiment1 where
data Showable = forall x. Show x => Showable…
Rehno Lindeque
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Resolving super-class constraints in a static form
I want to write a typeclass for types that have a static pointer to a dictionary that can discharge the super class constraints. In this contrived example the super-constraint is Typeable, since modern GHC versions automatically provides the…
cdk
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Haskell: interaction between ConstraintKinds, and TypeSynonymInstances
I'm getting an unexpected error when trying to compile a small Haskell file with GHC 8.6.1 when using ConstraintKinds and TypeSynonymInstances.
I'd like to make a class that takes a class as a parameter, and I'd like to use an alias when writing an…
Fried Brice
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Higher kinded type on typeclass?
To find out, if a type is a higher kinded type ghci provide:
Prelude> :k Maybe
Maybe :: * -> *
And tried on typeclass like:
Prelude> :k Functor
Functor :: (* -> *) -> Constraint
Why can I ask for higher kinded type on typeclass? What does…
softshipper
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