I have some problems with enabling debugging output. I have broken the compiler in such a way that for some programs I'm getting compiler panic when using some of the flags (-ddump-simpl, -fhpc): Main.h :: GHC.Types.Float -> GHC.Base.String [GblId, Arity=1, Str=DmdType] Main.h =ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20130422 for x86_64-unknown-linux): Impossible case alternative I would like to get output from the assertions and warnings placed in the code, for example in this function in simplCore/Simplify.lhs (this is the source of my error message): missingAlt :: SimplEnv -> Id -> [InAlt] -> SimplCont -> SimplM (SimplEnv, OutExpr) missingAlt env case_bndr _ cont = WARN( True, ptext (sLit "missingAlt") <+> ppr case_bndr ) return (env, mkImpossibleExpr (contResultType cont)) I recompiled GHC with the -DDEBUG option, but when I add -debug flag during program compilation I see no output from WARN directive. Are there any additional options I need to enable? Janek P.S. My build.mk has these lines: BuildFlavour = quick ifeq "$(BuildFlavour)" "quick" SRC_HC_OPTS = -H64m -O0 -fasm GhcStage1HcOpts = -O -fasm -Werror -Rghc-timing -DDEBUG GhcStage2HcOpts = -O0 -fasm -Werror -Rghc-timing -DDEBUG GhcLibHcOpts = -O -fasm SplitObjs = NO HADDOCK_DOCS = NO BUILD_DOCBOOK_HTML = NO BUILD_DOCBOOK_PS = NO BUILD_DOCBOOK_PDF = NO endif