On Tue, Nov 20, 2012 at 7:53 AM, Mathijs Kwik <mathijs@bluescreen303.nl> wrote:

KC <kc1956@gmail.com> writes:

> Instead of Haskell running on the JVM is there a way for Haskell to
> call a JVM language (or generate bytecode) to access the Java class
> libraries when needed?

I once did a small test to get this working.
It's not that hard, but needs some work. It's fine for exposing a few
functions though.

Basically it's a 2-step process, eased by using a makefile or similar
helper.

You have to compile your haskell code into a shared object (.so on
linux, .dll on windows), which includes the haskell runtime (rts).

This library can be called from c.
A small pitfall is that you first need to do a call to initialize the
haskell runtime, and when you're done using it, close it.
This is most easily just tied to your c/java program's main
initialization functions.

Java is able to load/use these shared libraries through JNI.
Of course you lose your platform-independance, so if you want your java
application to work on multiple platforms / OSses, you need to build
shared objects for all of them.

Last but not least:
You have to export the haskell functions you want through FFI.
Also, make sure they use raw data types such as CString, as that what C
and java will give you and expect back.

So basically you go Haskell FFI <-> C <-> Java JNI

I'm sorry I cannot give you any links or code, because I'm in a bit of a
hurry. But google and the ghc docs are your friend.

Mathijs

>
> Or
>
> Is there a way for a JVM language or bytecode to call Haskell when needed?

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