Hi,

 

I have the following to .hs files:

 

1. MyLib.hs:
   
   module MyLib where
   …
   
   
2. Test.hs:
   
   {-# LANGUAGE PackageImports  #-}
   module Test where
   import “my-pkg” MyLib
   …

 

I would like to parse/typecheck/load MyLib.hs into some Unit “my-unit”, then add that to the package “my-pkg”, and then typecheck Test.hs, all in-proc using the GHC API, without putting any other files on disk. How do I do that?

 

What I tried is loading MyLib.hs after setting the homeUnitId in the DynFlags to “my-unit”, then editing the packageNameMap in the unitState of the DynFlags to may “my-pkg” to “my-unit”:

setHomeUnit :: (GhcMonad m) => UnitId -> m ()

setHomeUnit unitId = do

    dflags <- getSessionDynFlags

    modifySession $ \h -> h{ hsc_dflags = dflags{ homeUnitId = unitId } }

 

registerUnit :: (GhcMonad m) => PackageName -> UnitId -> m ()

registerUnit pkg unitId = modifySession $ \h -> h{ hsc_dflags = addUnit $ hsc_dflags h }

  where

    addUnit dflags = dflags

        { unitState = let us = unitState dflags in us

            { packageNameMap = M.insert pkg (Indefinite unitId Nothing) $ packageNameMap us

            }

        }

 

pipeline = do

        setHomeUnit myUnit

        loadModule =<< typecheckModule =<< parseModule =<< modSumarryFor “MyLib”

        registerUnit myPkg myUnit

 

        setHomeUnit mainUnitId

        typecheckModule =<< parseModule =<< modSumarryFor “Test”

 

 

Alas, this doesn’t work: the import of `MyLib` from `my-pkg` fails with:

 

input/linking/Test.hs:5:1: error:

    Could not find module ‘MyLib’

    It is not a module in the current program, or in any known package.

 

TBH I’m not very surprised that it didn’t work – that registerUnit function is doing some pretty deep surgery on the unitState that probably breaks several invariants. Still, I wasn’t able to find a better way – all the functions in GHC.Unit.State seem to be for querying only.

 

Thanks,

            Gergo