[Yhc] Yhc and plugins architecture

[Donald Bruce Stewart]

shackell:
> 
> On Sun, 2006-09-17 at 18:31 +0200, C??dric Paternotte wrote:
> > Hi,
> > 
> > I was wondering whether Yhc was able to provide dynamic loading of modules.
> > 
> > Let's say I'd wanted to do something like :
> > 
> > myFiboFunction <- loadModule "myPlugin.hbc" "myFiboFunction"
> > putStrlLn $ myFiboFunction 10
> > 
> > Is it possible to achieve this in the current state of Yhc ?
> > I know there's an API out there to load bytecodes at runtime but I'm
> > not sure it's meant to do that...
> 
> Hi Cedric, 
> 
> There is indeed a RuntimeAPI, though it's still in the process of being
> written so it's a bit low level. At somepoint we'll write a
> user-friendly library over the top but at present your example would be:
> 
> import YHC.Runtime.API
> 
> main = do
>     let typ = undefined :: Int -> Int
>     fibo <- loadFromModule "MyPlugin" "myFiboFunction" typ
>     putStrLn $ show $ fibo 10
>   
> loadFromModule :: String -> String -> a -> IO a
> loadFromModule mod obj typ = do
>     pluginModule <- moduleLoad mod
>     case pluginModule of 
>        Nothing -> error $ "couldn't load module '"++mod++"'"
>        Just m -> do
>          fiboNode <- moduleLookupNode m obj
> 	 case fiboNode of 
>            Nothing -> error $ "could not find '"++obj++
>                               "' in module '"++mod++"'"
>            Just n -> do
>              typRep <- getType typ
> 	     withNode n typRep $ \ fibo -> 
>               return fibo
> 
> Notice that it's necessary to give a dummy parameter of the correct type
> to keep the type system happy. Also be wary that the system currently
> doesn't check that the type is correct so doing:
> 
>    ...
>    let typ = undefined :: Float -> Char
>    ..
> 
> Will compile and even execute, but will prompty crash horribly. In
> future we'll add type checking so it'll give a sensible runtime error.
>   
> Hope that helps :-)

Hmm, from here it wouldn't be too hard I think to add 
    eval :: String -> IO a
would it?

eval s = do
    writeFile "tmp.hs" s
    yhc "-c" "tmp.hs" -- run the compiler, get a .o bytecode file (?)
    loadFromModule "tmp.o"  ..

or even a nicer interface might exist? Tom?

/me has visions of fast bytecode eval for lambdabot.

-- Don