VisibleTypeApplication and AllowAmbiguousTypes

Joachim Breitner mail at
Mon Mar 21 23:05:20 UTC 2016

Hi Richard,

along with this or some other change it seems you broke the test suite
when run with DEBUG:

T2478.hs:1:41: warning:
    -XDatatypeContexts is deprecated: It was widely considered a misfeature, and has been removed from the Haskell language.
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.1.20160321 for x86_64-unknown-linux):
	ASSERT failed!
  CallStack (from HasCallStack):
  assertPprPanic, called at compiler/typecheck/TcType.hs:931:47 in ghc:TcType

Please report this as a GHC bug:

*** unexpected failure for T2478(normal)

at least according to travis:


Joachim “nomeata” Breitner
  mail at joachim-breitner.de
  XMPP: nomeata at • OpenPGP-Key: 0xF0FBF51F
  Debian Developer: nomeata at

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