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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
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  • #7347
Closed
Open
Issue created Oct 19, 2012 by Simon Peyton Jones@simonpjDeveloper

Existential data constructors should not be promoted

Stefan Holdermans reports: I am almost sure this is a known issue, but I noticed some erroneous (?) interaction between datatype promotion and existential quantification. Consider the following program:

  {-# LANGUAGE DataKinds                 #-}
  {-# LANGUAGE ExistentialQuantification #-}
  {-# LANGUAGE GADTs                     #-}
  {-# LANGUAGE KindSignatures            #-}

  module Test where

  data K = forall a. T a  -- promotion gives 'T :: * -> K                          

  data G :: K -> * where
    D :: G (T [])         -- kind error!

I would expect the type checker to reject it, but GHC (version 7.6.1) compiles it happily

Trac metadata
Trac field Value
Version 7.6.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
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