Re: [Caml-list] polymorphic method.

[blue storm <bluestorm.dylc@gmail.com>]

On Thu, Sep 10, 2009 at 9:14 PM, Guillaume Yziquel
<guillaume.yziquel@citycable.ch> wrote:
> I'm not really familiar with syntax extensions. Can this 'polymorphic'
> keyword be implemented with a syntax extension?

No, it can't. If you're talking about camlp4 syntax extensions,
they're converted to regular OCaml programs at camlp4-time, wich is
*before* the compiler see the program. It thus can't access any type
information : you can have syntax extensions that send type
information to the typer, but not the other way around : only purely
syntaxic transformations are expressible.
With a camlp4 extension, you could inspect the (syntaxically explicit)
parameters of you method, and (syntaxically) generate a polymorphic
type for each one : "polymorphic method foo bar baz = ..." would be
translated into "method foo : 'a 'b . 'a -> 'b -> 'c = fun (bar : 'a)
(baz : 'b) -> ...".
This is probably not what you want. You could further enrich your
extension with a "param" keyword that would not generate polymorphic
types for some of the parameters "method foo bar (param baz) = ..", or
have the "poly" keyword be parameter-specific "method foo (poly bar)
baz = ...", but my general advice is not to try to much to do
type-level transformation by syntaxic transformations : they tend to
get flawed in ways you don't expect, and this is just not the right
tool for the job.