Hello, I am looking at how GHC generates STG and I am finding with a very simple piece of Haskell my usage of the API is not generating as much STG as I see when using -dump-stg option. In particular it isn't generating a binding for the nullary constructor LNull (I hope that's the correct terminology) The code is module Ex2 where data List a = LCon a (List a) | LNull -- deriving Show main :: List Int main = LCon 1 LNull Using the API I get [sat_s1pdQ = NO_CCS GHC.Base.I#! [1]; Ex2.main = NO_CCS Ex2.LCon! [sat_s1pdQ Ex2.LNull]; main = \u srt:SRT:[(s1pdS, Ex2.main)] [] Ex2.main;] with -ddump-stg I get a_r5Y = NO_CCS GHC.Base.I#! [1]; SRT(a_r5Y): [] Ex2.main = NO_CCS Ex2.LCon! [a_r5Y Ex2.LNull]; SRT(Ex2.main): [] Ex2.LCon = \r [eta_s67 eta_s68] Ex2.LCon [eta_s67 eta_s68]; SRT(Ex2.LCon): [] Ex2.LNull = NO_CCS Ex2.LNull! []; <---- This is missing SRT(Ex2.LNull): [] (in particular the Ex2.LNull is missing from the API STG) My thrown together API code is session <- GHC.newSession $ Just path (dflags,_) <- GHC.getSessionDynFlags session >>= Packages.initPackages GHC.setSessionDynFlags session dflags {GHC.hscTarget=GHC.HscAsm} core <- GHC.compileToCore session fp case core of Just core' -> do core'' <- corePrepPgm dflags core' [] stg <- coreToStg (PackageConfig.stringToPackageId "Ex2") core'' putStrLn $ (show $ (ppr stg) defaultDumpStyle) Nothing -> return () Mark