replacing guile with haskell?

[Alastair Reid]

> 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is an out of date version of this document but gives a reasonable overview.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