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Questions - data-kinds

What does the `forall a -> b` syntax mean?

In GHCi, the kind of FUN is displayed like this: λ> :k FUN FUN :: forall (n :: Multiplicity) -> * -> * -> * At first, I thought this was a roundabout way of saying FUN :: Multiplicity -&g...
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fluffyyboii

haskell

types

existential-type

data-kinds

forall

Votes: 0

Answers: 1

Latest Answer

forall a -> _ is used when the result type depends on an explicit argument. -- type NonDep :: Type -> Type; argument is explicit data NonDep (x :: Type) :: Type -- type ImpDep :: forall a. Maybe...
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HTNW

Converting between variants of a data type

Suppose I want to create two variations of a data type, one that has a certain constructor and one that does not have it, otherwise they are identical. I came up with this: {-# LANGUAGE KindSignatures...
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n. m. will see y'all on Reddit

haskell

gadt

data-kinds

Votes: 0

Answers: 0

Reify arbitrary data-kind to a (compile-time known) value

I want to be able to write something like: reify (Proxy @True)) == True; reify (Proxy @(Just 5)) == Just 5; Is it possible by a blanket implementation? I got as far as class Reify (a :: k) where re...
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MorJ

haskell

ghc

data-kinds

derivingvia

Votes: 0

Answers: 1

Latest Answer

I would be remiss if I didn't note that the best solution at the moment is still the singletons package, which provides the demote function to do what you want (see example at the end). However, that...
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K. A. Buhr

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