[Haskell-beginners] Passing data between programs.

[MAN]

I've had this problem for a while now, and it's about time I recognize I
need help :P
I've written a few programs in Haskell that excel at numeric and/or
complex computations; I love the efficiency of the language. I do not
love, however, writing GUIs for this pieces of software.
Perhaps it's the echoes of bad times past when trying to install gtk2hs,
or that I know I can crank up some decent UIs in other languages faster.
Whatever the reason, I've been thinking of writing the GUI for my
programs as an extension of the program itself, possibly in another
language.
Assuming the GUI is written in, say, Python, and want to pass data to
the underlying Haskell program, how to send it? I'd like to avoid
touching the disk, but I don't have enough experience to answer my own
questions:
- command line arguments? what if data is large?
- client GUI, server Haskell program, and unix sockets? is there a
simpler way?

Any insights, comments, or experience shared will be greatly
appreciated. Thanks.