Hi all, Could you offer some insight into newtypes at the STG level? Here’s the context:
1. I’m working on this interpreter for STG (https://github.com/chrisdone/prana) and I’m trying to generate a pristine AST where all names in it are resolved to something known to me. 2. I’ve compiled ghc-prim and integer-gmp without issue, and I’m compiling base and there remains one last frontier which is newtypes. These are the culprits pointed out if I compile base: chris@precision:~/Work/chrisdone/prana/ghc-8.4/libraries/base-4.11.1.0$ PRANA_INDEX=../prana.idx stack build --exec './Setup build --ghc-options=-O0' --file-watch Preprocessing library for base-4.11.1.0.. Building library for base-4.11.1.0.. [1 of 244] Compiling GHC.Base [2 of 244] Compiling GHC.IO [3 of 244] Compiling GHC.Real [4 of 244] Compiling Data.Semigroup.Internal ... [snip] ... [242 of 244] Compiling Data.Functor.Compose [243 of 244] Compiling Data.Fixed [244 of 244] Compiling Data.Complex Errors in Data.Foldable: Variable name not found: base:Data.Semigroup.Internal.All Variable name not found: base:Data.Semigroup.Internal.Any Errors in Foreign.Marshal.Pool: Variable name not found: base:Foreign.Marshal.Pool.Pool Errors in GHC.ExecutionStack.Internal: Variable name not found: base:GHC.ExecutionStack.Internal.StackTrace Errors in Data.Bifoldable: Variable name not found: base:Data.Semigroup.Internal.All Variable name not found: base:Data.Semigroup.Internal.Any Errors in System.Timeout: Variable name not found: base:System.Timeout.Timeout Errors in Data.Data: Variable name not found: base:Foreign.Ptr.WordPtr Variable name not found: base:Foreign.Ptr.IntPtr Variable name not found: base:Data.Semigroup.Internal.Any Variable name not found: base:Data.Semigroup.Internal.All I looked these up, and they all appear to be *uses* of a newtype. For example, in the Timeout function: http://hackage.haskell.org/package/base-4.12.0.0/docs/src/System.Timeout.html#timeout I printed out the full [StgTopBinding] list and got: let { sat_s27NC [Occ=Once] :: IO Timeout [LclId] = [] \u [] fmap $fFunctorIO Timeout newUnique; } in >>= $fMonadIO sat_s27NC sat_s27NT; Oddly (or not?), they’re used as values, not constructors. This error comes from this part of my code: StgSyn.StgApp occ arguments -> AppExpr <$> lookupSomeVarId occ <*> traverse fromStgGenArg arguments If it was used as a constructor, it’d appear in this position, where looking up the ID would produce a “Data constructor name not found” error: StgSyn.StgConApp dataCon arguments types -> ConAppExpr <$> lookupDataConId dataCon <*> traverse fromStgGenArg arguments <*> pure (map (const Type) types) My understanding of newtypes at this stage is hazy. It seems like: - They ought to be erased and replaced with coercions by now. If they’re not replaced, it’s because they’re in a not-quite-id position like fmap Timeout .... (Arguably these could be fixed in base with a Data.Coerce.coerce?) - However, the CoreTidy/PrepPgm processing modules don’t seem to have removed or replaced these, or introduced a binding that would do something. At this stage what would you recommend? At this point type-checking is done, and I only care about interpreting the code. So I suppose they could be id for all it matters to the interpreter? I imagine they aren’t actually supposed to allocate something here. And I’m certain that any pattern matching on a newtype is also erased away by this point. Cheers! Chris
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