Has anyone seen this kind of error from GHC? dca9047d694f:concat-learn a594349$ stack build :lenna concat-learn-0.2.0.0: build (lib + exe) Preprocessing library concat-learn-0.2.0.0... [6 of 6] Compiling ConCat.Learn.CNN.Conv ( src/ConCat/Learn/CNN/Conv.hs, .stack-work/dist/x86_64-osx/Cabal-1.24.2.0/build/ConCat/Learn/CNN/Conv.o ) user error (Unexpected result from the SMT solver: Expected: success Result: (error "line 1515 column 22: unknown constant tn_1" ) ) -- While building custom Setup.hs for package concat-learn-0.2.0.0 using: /Users/a594349/.stack/setup-exe-cache/x86_64-osx/Cabal-simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2 --builddir=.stack-work/dist/x86_64-osx/Cabal-1.24.2.0 build lib:concat-learn exe:lenna --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 I started seeing it when I started trying to use the someNatVal function.