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  • Glasgow Haskell CompilerGlasgow Haskell Compiler
  • GHCGHC
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  • #12785
Closed
Open
Issue created Oct 30, 2016 by Gabor Greif@ggreif💬Developer

GHC panic, `tcTyVarDetails` is missing a case

Compiling the attached module I get

$ ghc --interactive Tree.hs 
GHCi, version 8.1.20161030: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Tree             ( Tree.hs, interpreted )

Tree.hs:28:63: error:ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20161030 for x86_64-apple-darwin):
	tcTyVarDetails
  cobox0_a1eK :: (m_a1ej[sk:2] :: Peano)
                 ~#
                 ('S n_a1eJ[ssk:3] :: Peano)
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in ghc:Outputable
        pprPanic, called at compiler/basicTypes/Var.hs:457:22 in ghc:Var

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

When switching the call to SBranchX in line 29 to a call to SBranch the program compiles. So I suspect that the problem is rooted in the extra constraint attached to constructor SBranchX.

Trac metadata
Trac field Value
Version 8.1
Type Bug
TypeOfFailure OtherFailure
Priority normal
Resolution Unresolved
Component Compiler
Test case
Differential revisions
BlockedBy
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Blocking
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Operating system
Architecture
Edited Mar 10, 2019 by Gabor Greif
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