I'm wondering what the possibilities are for replacing the use of guile with a haskell interpereter? I'd like to be able to embed a haskell interpereter (presumably hugs) withing my program, so that the input file could be a haskell program.
Do you want to embed Haskell code or to embed a Haskell interpreter? Embedding Haskell code is supported by the ffi specification and, in particular, by GHC which will give good performance and trustworthy numeric results.
Currently, my best (and only) idea is to make the input file a script with #!/usr/bin/env runhugs at the top (and compiling an interface module with ffihugs).
You might get a little more value out of the Hugs server interface which lets you unload and reload modules, etc. See hugs98/docs/server.{html,tex}. The documentation on http://www.reid-consulting-uk.ltd.uk/alastair/publications/hugs-server/ server.ps.gz is an out of date version of this document but gives a reasonable overview. Googling for "hugs server" will find you various articles about using this API.
There are a couple of issues with this. The first is that I've heard that hugs isn't intended for numerical work (which is what I'm doing). I'm not sure if this will be a problem, since hugs won't be doing any of the real work anyways.
It's hard to comment on this. Hugs numeric routines are a lot better than when the original "don't use" advice was written - but people do complain every now and then.
The other is that according to the man page, it seems that hugs only supports ffi on x86, powerpc and sparc, which seems likely to be a show stopper. Since I'll need to run the code on supercomputers, I won't always have a choice of architectures, and at least support for POWER (maybe comes free with powerpc?) would be necesary--IBM SP machines are quite nice. In this regard, ghc seems worse than hugs (the thought of bootstrapping ghc on a supercomputer gives me the shivers), and nhc98 last time I looked didn't support 64 bit platforms.
It's only calling Haskell functions from C which is non-portable. Unfortunately, I'd guess that's the bit you need! Porting Hugs' ffi to a new platform is pretty easy for someone with assembly code experience since you only have to write one function - albeit a tricky one. Less if ghc has already been ported to that platform since we can steal code from them :-) The code involved is the function 'mkThunk' in hugs98/ src/builtin.c GHC is available for powerpcs so it's probably just the operating system that will cause trouble. I would guess that nhc is easy to port to 64 bit machines since (at least some) C compilers provide flags to compile for 32-bits. But I could easily be wrong... [Note: both GHC and NHC will need pretty much the same assembly code magic that Hugs needs.] -- Alastair Reid www.haskell-consulting.com