The symbols must be exported from the main program... I think you can pass the linker an option to force it to export symbols. Keean. Fraser Wilson wrote:
Hi there,
I would like to use evaluate arbitrary expressions in the context of a mixed-language (Ada, Haskell and about twelve lines of C glue) applications. Is it possible to use dynload from hs-plugins to load a module that references symbols in the loading program?
For example, the application contains a Haskell module that looks a bit like this:
module TestKeys.NamedObject where tt :: Int tt = 2
I want the application to be able to offer the following sort of interaction:
haskell> tt 2 haskell>
But what actually happens is this:
haskell> tt test_haskell3: /tmp/MDnum15633.o: unknown symbol `TestKeysziNamedObject_tt_closure' test_haskell3: user error (resolveObjs failed with <<False>>)
Compiling Haskell code in advance works (i.e. if I create and compile a module that evalutes tt and link it in, everything runs fine).
This is how I try to evaluate the expression:
evaluate :: String -> IO () evaluate "" = return () evaluate e = do writeFile "temp.hs" fileContents status <- makeWith "LeanderStub.hs" "temp.hs" ["-c"] case status of MakeSuccess code path -> loadAndEval path MakeFailure error -> print error where fileContents = "module Temp where\n\ \ result = " ++ e ++ "\n"
loadAndEval :: FilePath -> IO () loadAndEval path = do mv <- dynload path [] [] "result" case mv of LoadFailure msg -> print msg LoadSuccess _ v -> putStrLn v
LeanderStub.hs is a module containing the necessary imports for the expression to evaluate in the right context.
I was hoping that passing "-c" to makeWith would create an object file whose missing dependencies would be resolved when it was loaded into an application which contained them. Is this a dumb expectation? The alternative -- linking to the entire application for each expression evaluated -- seems a bit over the top, and I can't see how state would be maintained.
I originally used unsafeEval_, but this has the same problem.
I can't help but think that this must have been done before. Any advice? If you know Guile, then the equivalent of gh_repl is what I'm really after.
cheers, Fraser.
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