[Haskell-beginners] alternative sourcegraph

I want to remove 'dead' code and unnecessary exports out of modules. I tried sourceGraph with sourceGraph tbGlasDll.hs and I got: Could not parse source file ./Toetsing.hs Could not parse source file ./TestGlas.hs Could not parse source file ./TBGlasDll.hs Could not parse source file ./Glas.hs Could not parse source file ./CalcGlas.hs Could not parse source file ./calc.hs Could not parse source file ./BelastingFactoren.hs sourceGraph: Map.findMin: empty map has no minimal element The files above compile without errors with ghc. Maybe it has to do with Template Haskell code? Is there an alternative to sourceGraph? Kees