[Caml-list] Call for collaboration on the future of camlp4

[oleg@okmij.org]

Hongbo Zhang wrote:
  > Meta-ocaml is orthogonal to camlp4 as well, but I did not see any hope
  > that it will be pushed into ocaml compiler,
  > since the main purpose of meta-ocaml is to do some run-time
  > optimization, without a native jit compiler support, It does
  > not make sense.

I believe you might be short-changing MetaOCaml. First of all, why
MetaOCaml needs JIT? It is already possible in MetaOCaml to generate
code at run-time, to compile it and link-in. The new code is generated
by the OCaml compiler itself, and works as if it were part of the
original code. Such run-time optimization can indeed be useful (e.g.,
profile-based optimization). I don't see why we need JIT if we already
have the original compiler itself.

However viewing MetaOCaml as a run-time optimizer misses a
lot. MetaOCaml is a code generator with certain assurances of
correctness -- it generates code that one would not write by hand. The
recent example of generating code for stencil computations in
high-performance computing

	http://okmij.org/ftp/meta-programming/HPC.html#stencil

was quite illustrative: MetaOCaml has generated code for edge
cases that human really did not want to write (and did not actually
write). Edge cases are really tedious and really difficult to get
right; automation is of great help. The generated code can be
printed-out and used in a project as any other code. MetaOCaml can be
used to generate libraries of specialized high-performance code.

  > Personally, I prefer common lisp's macros to scheme. It's painful
  > to play with racket's macros as well

Well, it is painful for some people to use typed languages
too. Untyped languages offer so much freedom, some think. What is
often forgotten is that the benefit of the type system is not in what
code you can write, but what code you cannot. Likewise, a syntax
extension should be evaluated not only on what it allows but also on
what it prevents.


As I general remark: it is not clear why so much fixation on
camlp4. Other people have tried extensible syntaxes. For example:

	- Felix
	- Notation of Coq
	- Stratego
	http://strategoxt.org/
In particular, see
	http://strategoxt.org/Sdf/SdfLanguage

Stratego could do program transformations in concrete syntax. Maybe
that would be a better approach? Maybe Stratego would satisfy all our
needs?