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[Caml-list] Camlp4: generating printers of types
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Date: 2002-12-10 (02:02)
From: Ken Rose <kenarose@e...>
Subject: Re: [Caml-list] Camlp4: generating printers of types
Daniel de Rauglaudre wrote:
> Hi everybody,
> In Camlp4 tutorial (current version), I added a section explaining how
> to make a syntax extension which, when loaded, automatically generates
> printers of all your types:
> For example, if your input file contains:
>     type colour = Red | Green | Blue
> this will be interpreted like this:
>     type colour = Red | Green | Blue
>     let print_colour =
>       function
>         Red -> print_string "Red"
>       | Green -> print_string "Green"
>       | Blue -> print_string "Blue"

I've been working on extending this to more general types, which I
suppose would be easy for someone who's had some practice with camlp4. 
I'm running into 2 problems, and anticipating a third one.

1. Is there a clean way to handle (sum) types with constructors with
multiple module qualifications?  I hacked the example to deal with, but it doesn't seem to extend automatically to Foo.Bar.baz.  As
I understand it, I'd need a new pattern for each additional uid.

2. How are tuples represented in camlp4's syntax?  This is so I can
match them when analyzing a type.

3. This is the big one.  When working on a type like:

type t = int

with the obvious extention to Daniel's code, the preprocessor produces

type t = int let rec print_t = print_int

Which the compiler rejects with "This kind of expression is not allowed
as right-hand side of `let rec'"  I haven't been able to figure out a
way to sneak it past, either.  What's going on here?  Why can't I rename


 - ken
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