[Haskell-cafe] Talking to Java from Haskell?

Jason Dagit dagit at codersbase.com
Thu Jul 8 21:58:56 EDT 2010

On Thu, Jul 8, 2010 at 6:35 PM, Daniel Cook <danielkcook at gmail.com> wrote:

> Hi,
> Someone has written a large Java library (QuickFIX/J) which speaks a
> gnarled, ugly protocol (FIX).  There don't appear to be any FIX
> protocol libraries in Hackage.  I need my Haskell program to talk to a
> 3rd-party system that only speaks FIX.
> Should I:
> a) Reimplement the protocol directly Haskell?  (This appears to be
> non-trivial)
> b) Wrap the Java library with some code to use a lightweight message
> queue (zeromq) to send messages to my Haskell program?  (This would
> require essentially re-implementing an abstracted subset of the the
> protocol into 0MQ messages)
> c) Find a way for Haskell to interact directly with Java? (the various
> JNI bridges seem very unmaintained...)

Are you referring to projects like these?
* lambdaVM: http://www.cs.rit.edu/~bja8464/lambdavm/

* EclipseFP uses (or used, I'm not sure) a bridge between Java/Haskell.

I doubt these approaches are very mature for general purpose work.  They
probably work well for the author's original purpose, but perhaps you'd run
into low level bugs using them yourself.  I assume they use Java's JNI and
connect that to Haskell FFI.  I don't know why this would be a necessarily
hard problem.  Haskell's FFI is very nice for talking to C, but perhaps
Java's JNI is not as friendly.

I would probably start by writing a JNI wrapper around QuickFIX to expose it
to C and C-like languages.  Then I would write a Haskell FFI binding to that
library.  In this way, C will become your glue language as odd as that may

As a longer term solution, having a combinator library for FIX in Haskell
sounds really nice.  I don't need it personally, but it just seems like the
way to go.  The drawback here is that you will have to duplicate a lot of
effort to keep your implementation in sync with the de facto implementation.
 On the other hand, depending on the nature of the technical hurdles your
Haskell implementation may be significantly easier to maintain and could
possibly end up serving as a concise, correct, reference implementation when
the FIX specification changes.

It's also possible that some Haskell compiler, such as YHC, would serve well
here.  Maybe it's easier to modify that in the way lambdaVM is a
modification to GHC.  If I recall correctly, YHC had a backend for
JavaScript at one point.  That makes me think it has a very hackable

Another possibility that tends to work very well is to use Haskell to define
a domain specific language.  Your DSL could generate Java source that uses
QuickFIX directly.  You get the strength of using the de facto tool chain
for your production binaries, the power of Haskell for language design, and
the expressive power that comes from having a domain specific language.
 This solution is also cheaper than it might sound.  You start with
combinators that build up Java expressions and go from there.

It's hard for me to say which is best without knowing more about the
programs you'll be writing.

Sounds like an interesting project!

Good luck,
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