If you want a better experience with metaprogramming, I definitely
recommend MetaOCaml (http://www.metaocaml.org). Unlike Template
Haskell, it is fully typed; TH only types the result of the generation,
not the generator itself [though SimonPJ assures me they are working on
that too].
Gabriel Dos Reis wrote:
(On performance side, last month, a colleague of mine and I did some
experiments by writing a small Computer Algebra library in Haskell 98
and Generic Haskell. Disappointingly, there is a slowdown factor
between 7 and 10 when going from Haskell to Generic Haskell. We don't
know yet which part can be credited to the maturity of the compiler
and which part is inherent to the approach. Anyway, it was an
interesting experience).
Is this experiment available? I would be quite interested in looking at
the details.
<ShamelessPlugWarning>
Getting efficiency from meta-programs seems to be quite difficult, and
even more so in a typeful system. Enough has been said about C++
template programming to assure everyone that a) it is hard, and b) it's
not *really* typed. But it *is* possible to get both genericity and
efficiency. As a side effect, one can also get much better code
organization as well! See the paper
"Multi-stage programming with functors and monads: eliminating
abstraction overhead from generic code" by Carette & Kiselyov
(paper, code, tests, etc at http://www.cas.mcmaster.ca/~carette/metamonads/)
published at GPCE05 (http://dx.doi.org/10.1007/11561347_18)
as well as http://metaocaml.org/examples/gausselim/
which contains all the extras for an earlier paper published (later!) in
Science of Computer Programming
(http://dx.doi.org/10.1016/j.scico.2005.10.012).
You will see, especially in the GPCE05 work, code organization which is
explicitly influenced by Axiom/Aldor. The principal reason that this
work was done in MetaOCaml was that a) the type system is completely
described (and proven to 'work') in published papers and b) the compiler
sources are open [which was needed, not just nice-to-have].
Our basic thesis is that, given the right infrastructure, you can
structure code like it ought to be structured (which is already what
Axiom/Aldor strives for) and, without relying on the cleverness of
compiler writers, get optimal efficiency. For linear algebra, this
works. In separate work, it was shown that this works for FFT as well.
We are currently extending the work to handle (numeric) solving of LODEs.
</ShamelessPlugWarning>
Jacques
PS: MetaOCaml has no introspection features at _all_, by design. No
'has' of anything like it. That makes things extra-challenging, yet
still feasible, which was not clear at all when the work was begun.
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