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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
  • Issues
  • #15289
Closed
Open
Issue created Jun 18, 2018 by Remi@trac-Remi

isUnliftedType GHC panic on pattern with True :: Maybe

{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Oops where

pattern What = True :: Maybe

Fails on 8.4.3 with:

ghc: panic! (the 'impossible' happened)
  (GHC version 8.4.3 for x86_64-unknown-linux):
	isUnliftedType
  (Maybe |> {co_a1Dg3}) :: TYPE t_a1Dg9[tau:1]
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
        pprPanic, called at compiler/types/Type.hs:1939:10 in ghc:Type

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

I'm currently cloning from git, and will try to get around to check it with HEAD over the next days. BTW, it's not a show-stopper for me.

Trac metadata
Trac field Value
Version 8.4.3
Type Bug
TypeOfFailure OtherFailure
Priority low
Resolution Unresolved
Component Compiler (Type checker)
Test case
Differential revisions
BlockedBy
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Blocking
CC
Operating system
Architecture aarch64
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