jhc0033:
I don't know Haskell very well, but even I can tell, looking at, for example, the N-body benchmark, that the Haskell code is probably not type-safe, and the tricks used in it would not be usable in a larger program (see below).
The task is essentially a pure computation: take a list of bodies having mass, position and velocity; apply Newton laws at discrete intervals for a large number of times; return new positions and velocities.
I could write a C++ procedure that performs this task and have some piece of mind regarding its type correctness, exception safety and functional purity: side effects would be local to the procedure, arguments passed as const or by value, the result returned by value, no type casts or new/delete operators used.
On the other hand, the Haskell code makes assumptions about the size of double-precision floats (obviously not type-safe). Further, the simulation is not a pure function.
It is often argued that one only needs these dirty tricks in the most time-consuming functions. However, if using imperative programming in these "inner loop" procedures places them in IO monad, the "outer loops" (the rest of the program - procedures that call it) will have to go there as well. This makes me doubt the Haskell approach to functional programming.
If anyone has a version of the N-body benchmark, where the simulation is a type-safe pure function, I would very much like to see and time it.
n-body requires updating a global array of double values to be competitive performance-wise, though we haven't really nailed this benchmark yet. The current entry should be considered an older approach to raw performance -- typically we can get good (or better) results in using the ST monad. To improve safety, it should run in the ST monad. A version using ST is here, http://haskell.org/haskellwiki/Shootout/Nbody However, the current fastest program should really be cross-ported to run in ST, for best results. (Similar to the nsieve-bits program): http://shootout.alioth.debian.org/gp4/benchmark.php?test=nsievebits&lang=ghc&id=0 I suspect the optimisations that weren't happening, that forced nbody to use Foreign.Ptr in the first place are likely obsolete now -- GHC 6.8.2 should do a good job with STUArray Double, in careful hands. Also worth looking at is the other purely functional entry, in Clean, http://shootout.alioth.debian.org/gp4/benchmark.php?test=nbody&lang=clean&id=0 translation to Haskell should be fairly straightforward. -- Don