constraint-kinds Questions
3
I searched Hackage and couldn't find anything like the following but it seems to be fairly simple and useful. Is there a library that contains sort of data type?
data HList c where
(:-) :: c a =&...
Reaganreagen asked 12/9, 2017 at 1:27
1
Solved
I can write the following:
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE ConstraintKinds #-}
f :: Integral a => (forall b. N...
Sodom asked 7/5, 2017 at 2:55
1
Solved
What is a Constraint kind?
Why would someone use it (in practice)?
What is it good for?
Could you give a simple code example to illustrate the answers to the previous two questions?
Why is it...
Retaretable asked 9/7, 2015 at 12:13
2
Solved
If I inspect the kind of Maybe I get this:
λ> :k Maybe
Maybe :: * -> *
Now, if I inspect the kind of Monad I get this:
λ> :k Monad
Monad :: (* -> *) -> Constraint
What is Const...
Current asked 8/4, 2015 at 8:37
3
Apparently a bit absent-mindedly, I wrote something like the following:
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE TypeFamilies #-}
class Foo f where
type Bar f :: *
retbar :: Bar f -> IO...
Jelle asked 5/4, 2015 at 21:56
2
Solved
I'm trying to derive a Typeable instance for tupled constraints. See the following code:
{-# LANGUAGE ConstraintKinds, GADTs #-}
{-# LANGUAGE DataKinds, PolyKinds, AutoDeriveTypeable #-}
{-# LANG...
Chicanery asked 17/9, 2014 at 14:19
1
Solved
Headline: I would like to provide a default implementation for a class method parametrised over a constraint, which uses the default instance for that constraint.
Consider the following:
{-# LANG...
Daune asked 28/7, 2014 at 14:32
1
Solved
I want just
class Trivial t
instance Trivial t
This is of course useless in Haskell 98 since you can just omit the constraint; but with ConstraintKinds we can have explicitly required arguments ...
Bestialize asked 6/2, 2014 at 14:0
1
Solved
When I have a data type like the following in haskell:
data A ctx = A (forall a. ctx a => a -> a)
Then I can put functions that work on values of types of a given class into this datatype:...
Bustup asked 22/6, 2013 at 18:33
1
Solved
I want to implement a dynamic programming algorithm polymorphic in the score type; here's a simplified 1D version with no boundary conditions:
{-# LANGUAGE ConstraintKinds, FlexibleContexts, RankN...
Empress asked 9/3, 2013 at 14:37
1
Solved
We can use the extension ConstraintKinds to extend the functionality of the base type classes to allow constraints. For example, we can make an unboxed vector a functor:
class Functor f where
typ...
Ignatia asked 2/10, 2012 at 19:57
1
Solved
I'm getting an error that Constraint is not in scope, when I try to write a simple example,
{-# LANGUAGE UndecidableInstances,
MultiParamTypeClasses,
KindSignatures,
Rank2Types,
ConstraintKind...
Hamachi asked 26/2, 2012 at 4:31
1
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