Hi Dan, On Friday 04 Mar 2011 21:59:12 Daniel Peebles wrote:

I'm adding Ed to the conversation as he's very interested in this topic, too.

I do apologise - I was meant to post the previous email back to haskell-cafe but by mistake it went only to you. I hope you do not mind that I am taking the discussion back to the cafe. I attach my email so that other readers of the cafe can see it.

The experts were right about it being impossible to work with GHC's GMP – until recently. "foreign import c" calls are indeed going to call GC when you don't want it, but when they split integer-gmp out of GHC's own RTS, Duncan Coutts (one of those experts) added the "foreign import prim" construct so that he could do exactly what you want, and operate on GMP integers with GHC-allocated memory without worrying about temporary storage blowing up while you aren't looking.

So in general, I'd lean more towards replacing all your ccall bindings to MPFR with cmm bindings. It does require some GHC internals knowledge but is fairly mechanical, and would solve all the problems, without requiring a rewrite of GMP (that would be slower anyway).

Ed is actually going to get started on a fairly simple binding to a subset of MPFR for one of his projects, using the CMM approach based on the structure of my natural-gmp package (https://github.com/pumpkin/natural-gmp, which is itself based heavily on integer-gmp, but reworked to work fine from cabal rather than depending on GHC's build process). Once he is done with that, you might want to refer to his implementation to make your more complete MPFR binding work with integer-gmp (and thus make no speed sacrifices).

If this is the best approach, I would welcome help with this as I will not have much time to work on it until the summer due to teaching commitments and the need to publish work done earlier.

I would also like a gmp-compatible replacement, but it's going to necessarily be slower and would prefer to be able to have fast computations over floating-point numbers AND integers/naturals.

Eek, I made a mistake, I apologise again - the proposal I was quoting in the announcement is not what I had in mind. I was meant to refer to a mention by igloo at the very end of http://hackage.haskell.org/trac/ghc/ticket/311 which is a very different proposal from the one I linked to and the one you seem to refer to here. I was not at all thinking of writing a gmp compatible replacement. I was thinking of taking gmp sources and mechanically modify the exported names and modify integer-gmp to use those modified names. Thus there would be no difference in the speed of Integer as it would still use an exact clone of the original gmp in exactly the same way as now but not interfere with what the usual gmp code does via other libraries. Please correct me if I this approach is not feasible or if there is some advantage in using cmm over this proposal that I am missing. Michal -- |o| Michal Konecny |o| http://www-users.aston.ac.uk/~konecnym/ |o| office: (+42) (0)121 204 3462 |o| PGP key http://www-users.aston.ac.uk/~konecnym/ki.aston