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The following program triggers a bug in 8.2.2 and 8.5.20171215.

-- Checks that the ordering constraint on the groupWith function is respected
{-# OPTIONS_GHC -XMonadComprehensions -XTransformListComp #-}
module ShouldFail where
import GHC.Exts (groupWith)
data Unorderable = Gnorf | Pinky | Brain
foo = [ ()
      | Gnorf <- [Gnorf, Brain]
      , then group by x using groupWith
      ]

Reproduce:

ghc bug.hs

Output:

` [1 of 1] Compiling ShouldFail ( bug.hs, bug.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.5.20171215 for x86_64-unknown-linux): tcSyntaxOp "noSyntaxExpr" Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcExpr.hs:1436:31 in ghc:TcExpr

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

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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