#14591: HEAD panic: tcSyntaxOp "noSyntaxExpr" -------------------------------------+------------------------------------- Reporter: tianxiaogu | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Linux Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following program triggers a bug in 8.2.2 and 8.5.20171215. {{{#!hs -- 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}}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14591 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler