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  • #13603

Closed
Open
Opened Apr 22, 2017 by Icelandjack@IcelandjackReporter

Can't resolve levity polymorphic superclass

This works

{-# Language PolyKinds, TypeInType #-}

import GHC.Exts (TYPE, RuntimeRep)

class        A (a :: TYPE rep)
class A a => B (a :: TYPE rep)

instance A b => A (a -> (b :: TYPE rep))
instance B b => B (a -> b)

but the moment you add (b :: TYPE rep) to the last line it stops working

-- t3I7.hs:9:10-40: error: …
--     • Could not deduce (A b)
--         arising from the superclasses of an instance declaration
--       from the context: B b
--         bound by the instance declaration at /tmp/t3I7.hs:9:10-40
--     • In the instance declaration for ‘B (a -> b)’
-- Compilation failed.

{-# Language PolyKinds, TypeInType #-}

import GHC.Exts (TYPE, RuntimeRep)

class        A (a :: TYPE rep)
class A a => B (a :: TYPE rep)

instance A b => A (a -> (b :: TYPE rep))
instance B b => B (a -> (b :: TYPE rep))
Trac metadata
Trac field Value
Version 8.0.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
Assignee
Assign to
8.2.1
Milestone
8.2.1 (Past due)
Assign milestone
Time tracking
None
Due date
None
Reference: ghc/ghc#13603