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[Caml-list] Camlp4: generating printers of types
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Date: 2002-12-10 (17:38)
From: Daniel de Rauglaudre <daniel.de_rauglaudre@i...>
Subject: Re: [Caml-list] Camlp4: generating printers of types

On Tue, Dec 10, 2002 at 07:33:23AM -0800, Ken Rose wrote:

> and so on into gen_print_type.  Or do I not understand what $uid:x$
> does?

If x is a string <:expr< $uid:x$ >> produces "the uppercase identifier
named by the value of x". If x is "Foo", this produces the identifier
Foo. Notice that it works even if x does not contain an uppercase
identifier: OCaml with interpret it as a module name or as a
constructor name (depending on its position), whatever its value.

Sorry, for your Baz.Baz.t, you need your <:ctyp< $uid:m2$.$uid:m$.$lid:s$ >>
The better is to use an iterator, or use the recursion to treat the
general case.

> > In Revised syntax, they are like in normal syntax, but the parentheses
> > are compulsory.
> Here, I want to match 
> type t = int * int
> within gen_one_print_fun, to produce a printer instead of "failwith...".

In Normal syntax, you can write "int * int" but inside the predefined
quotations of AST, you have to use the Revised syntax. See the chapter
about it in the reference manual.

You must write it <:ctyp< (int * int) >>. And if tl is a list of ctyp,
you can obtain the type tuple of this list of types with:
    <:ctyp< ($list:tl$) >>

See the chapter about AST quotations.

> > This message of OCaml just means that there are syntactic restrictions
> > of the "let rec". In this case, you should produce either a "let" without
> > "rec" or, an eta extension: "let rec print_t x = print_int x".
> I'd suspected that, though I'm still curious as to why that's so. 

Damien Doligez answered you on that point; this is typing and
therefore not the work of Camlp4.

> Still, what I really want is a generally useful tool to produce these
> useful functions, without having to spend too much time right now
> learning camlp4.  It's for my regular work, where I'm building a
> compiler for a DSL.  I don't understand camlp4 well enough to know how
> to suppress the "rec", and I'm hoping to avoid learning, at least for a
> while.  It's a great tool, but I have only so much time.

Well, if you don't have time to look at it, I can help.

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