Using GHC API with multiple targets

Andreas Klebinger klebinger.andreas at gmx.at
Mon Feb 6 12:53:36 UTC 2023


I think this is an ok forum for this kind of question. You could also
try the haskell mailing list but I'm not sure if you will get more
help tehre.

I recently played around with the ghc api and I found the `hint` package
to be quite helpful as an example on how to do various
things when using the ghc api to implement your own interpreter.

Have you tried setting verbose? Perhaps the include dir is relative to
the working directory. In that case setting:

                   , workingDirectory = Just targetDir
                   , importPaths      = [targetDir] ++ importPaths dynflags

would mean ghc will search in targetDir/targetDir for Lib/Lib2. Should
be easy to say for sure by enabling verbosity and looking at the output.

Am 06/02/2023 um 13:42 schrieb Eternal Recursion via ghc-devs:
> If this is the wrong forum for this question (which as I think about
> it, I suppose it is) then redirection to a more appropriate mailing
> list or forum (or any advice, really) would be appreciated. I just
> figured this would be the forum with the best understanding of how the
> GHC API works (and has changed over time), and my longer term goal is
> indeed to contribute to it after I get past my learning curve.
>
> Sincerely,
>
> Bob
>
> Sent with Proton Mail <https://proton.me/> secure email.
>
> ------- Original Message -------
> On Saturday, February 4th, 2023 at 4:04 PM, Eternal Recursion via
> ghc-devs <ghc-devs at haskell.org> wrote:
>
>> Hi Everyone!
>>
>> I'm new here, trying to learn the GHC API. using 944 with cabal 3.8.1.0.
>>
>> How do I correctly set a GHC Session's DynFlags (and/or other
>> properties) to ensure local libraries imported by the main target are
>> resolved properly at compile time?
>>
>> What flags need to be set so that GHC is able to load/analyze/compile
>> all relevant Libraries in a package?
>>
>> This is my current code:
>>
>> withPath :: FilePath -> IO ()
>> withPath target = do
>> let targetDir = takeDirectory target
>>   let targetFile = takeFileName target
>> listing <- listDirectory targetDir
>>   let imports = filter (\f -> takeExtension f == ".hs") listing
>>   print imports
>>   let moduleName = mkModuleName targetFile
>>   g <- defaultErrorHandler defaultFatalMessager defaultFlushOut
>>     $ runGhc (Just libdir) $ do
>> initGhcMonad (Just libdir)
>> dynflags <- getSessionDynFlags
>> setSessionDynFlags $ dynflags { ghcLink          = LinkInMemory
>>                           , ghcMode          = CompManager
>>                           , backend          = Interpreter
>>                           , mainModuleNameIs = moduleName
>>                           , workingDirectory = Just targetDir
>>                           , importPaths      = [targetDir] ++
>> importPaths dynflags
>>                           }
>> targets <- mapM (\t -> guessTarget t Nothing Nothing) imports
>> setTargets targets
>> setContext [ IIDecl $ simpleImportDecl (mkModuleName "Prelude") ]
>> load LoadAllTargets
>> liftIO . print . ppr =<< getTargets
>> getModuleGraph
>> putStrLn "Here we go!"
>>   print $ ppr $ mgModSummaries g
>> putStrLn "☝️ "
>>
>> However, when I run it (passing to example/app/Main.hs, in which
>> directory are Lib.hs and Lib2.hs, the latter being imported into
>> Main), I get:
>>
>> $cabal run cli -- example/app/Main.hs
>> Up to date
>> ["Main.hs","Lib.hs","Lib2.hs"]
>> [main:Main.hs, main:Lib.hs, main:Lib2.hs]
>> Here we go!
>> [ModSummary {
>>    ms_hs_hash = 23f9c4415bad851a1e36db9d813f34be
>>    ms_mod = Lib,
>>    unit = main
>>    ms_textual_imps = [(, Prelude)]
>>    ms_srcimps = []
>> },
>> ModSummary {
>>    ms_hs_hash = e1eccc23af49f3498a5a9566e63abefd
>>    ms_mod = Lib2,
>>    unit = main
>>    ms_textual_imps = [(, Prelude)]
>>    ms_srcimps = []
>> },
>> ModSummary {
>>    ms_hs_hash = 5f6751d7f0d5547a1bdf39af84f8c07f
>>    ms_mod = Main,
>>    unit = main
>>    ms_textual_imps = [(, Prelude), (, Lib2)]
>>    ms_srcimps = []
>> }]
>>>>
>> example/app/Main.hs:4:1: error:
>>    Could not find module ‘Lib2’
>>    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
>>  |
>> 4 |import qualified Lib2 as L2
>>  |^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> cli: example/app/Main.hs:4:1: error:
>>    Could not find module `Lib2'
>>    Use -v (or `:set -v` in ghci) to see a list of the files searched
>> for.
>>
>> ​What do I need to do differently to make this work?
>>
>> I have a local Cabal file I could use, but to know what I need out of
>> it, I need to understand the minimum required info to get this to
>> work. TIA!
>>
>> Sincerely,
>>
>> Bob
>>
>> Sent with Proton Mail <https://proton.me/> secure email.
>
>
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