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  • #13700

Closed
Open
Opened May 15, 2017 by Icelandjack@IcelandjackReporter

GHCi command listing possible type class instances

This is a reminder ticket,

I want to be able to list possible instances,

>>> :insts Product
(Functor     f, Functor     g) => Functor     (Product f g)
(Applicative f, Applicative g) => Applicative (Product f g)
...

>>> :insts Product Identity
Functor     g => Functor     (Product Identity g)
Applicative g => Applicative (Product Identity g)
Monad       g => Monad       (Product Identity g)
MonadFix    g => MonadFix    (Product Identity g)
MonadZip    g => MonadZip    (Product Identity g)
...

>>> :insts Product Identity Identity
Functor     (Product Identity Identity)
Applicative (Product Identity Identity)
Monad       (Product Identity Identity)
MonadFix    (Product Identity Identity)
MonadZip    (Product Identity Identity)

Would be so useful for GeneralizedNewtypeDeriving

newtype Pair a = P (Product Identity Identity a)
  deriving (Functor, Applicative, Monad, MonadFix, MonadZip, ...)

-- pattern (:#) :: a -> a -> Pair a 
-- pattern a1 :# a2 = P (Identity a1 `Pair` Identity a2)
Trac metadata
Trac field Value
Version 8.0.1
Type FeatureRequest
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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Reference: ghc/ghc#13700