Is it fine if the interface uses JNI? The jvm-bridge is an excellent tool if you can use JNI, but I don't know of anything that compiles Haskell to java bytecode. There was a post a few years ago about an experimental Java backend for GHC, but I haven't heard anything since, and the -J switch doesn't do anything in a recent GHC. The Mandarin people had a version of GHC back when they were targeting Java, but they've moved to .NET. Does anyone know of a project (or a CVS tag) for something that can compile Haskell to java bytecode? The jvm-bridge project includes tools for generating a Haskell interface to a java class, another for generating a monad that wraps the JVM initialization your program needs, using typeclasses to model the class hierearch and convert parameters. There is a function that will dynamically define a class with Haskell methods. I don't know how much support jvm-bridge provides if you want to define a class in Haskell and package it so you can use it from a normal java program. You would need to declare a class in java with native methods, and compile the haskell into a suitable library providing the native implementation. I don't remember any tools for doing this. I might have simply forgotten or overlooked a nice interface, or you might need to write the JNI code. If you are determined to go this way you could at least use the JNI binding JVM provides. Rather than doing that, it's probably simpler for your program to start in Haskell, even if all it does is define a class and invoke your main class (passing a factory object). I assume your haskell with need to call java at some point, if only to unpack a collection, so I'll pass along two things that confused me for a while. One thing to remember is that methods are defined in the class module for the first class that defined them. If you want to use a method that a class inherited from an ancestor you need to create and import the class module for that ancestor. The method will have a name like method_ancestor_args, but it calls the correct overridden method on whatever object you pass in a this (first argument). The other thing (this is more a Haskell issue) is that if you are writing a GUI program the main (Haskell) thread has to survive until the program is supposed to end, and it needs to be inside the "let java threads run" combinator. (sorry, I forgot the name and I'm away from my home machine). What are you trying to do? I'm thinking about porting a web testing application from python to haskell for parser combinators and monads (I'm using objects with a run method to control execution and thread through some state), but I don't know of any alternative to the HttpUnit library for testing webpages with javascript. I just need to call a bit of java in the middle of a Haskell program Tell us how your project works out. Brandon On 12 Aug 2003, Immanuel Litzroth wrote:
Calling Haskell from java was supposed to be supported by a tool called lambada, but all I can seen to find of that on the net is a paper. Does anyone have any pointers to more information/implementation. I specifically want to call Java->Haskell and not the other way around. thanks in advance Immanuel *************************************************************************** It makes me uncomfortable to see An English spinster of the middle class Describe the amorous effects of `brass', Reveal so frankly and with such sobriety The economic basis of society. W.H. Auden
-- Immanuel Litzroth Software Development Engineer Enfocus Software Kleindokkaai 3-5 B-9000 Gent Belgium Voice: +32 9 269 23 90 Fax : +32 9 269 16 91 Email: Immanuell@enfocus.be web : www.enfocus.be ***************************************************************************
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