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Custom lexer in Camlp4
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Date: 2008-06-24 (15:16)
From: Richard Jones <rich@a...>
Subject: Re: [Caml-list] Custom lexer in Camlp4
On Tue, Jun 24, 2008 at 03:30:23PM +0100, Jeremy Yallop wrote:
> Ok, I've built a slightly modified clone of PreCast.  What's the best 
> way to persuade Camlp4 to use it?  The original PreCast seems fairly 
> hardwired, e.g. in the Register module.

If you get an answer to this, please post it.  I would love to be able
to add new integer literals to the language (0UL and so on).

On a related note I had a crazy brainwave that we could use camlp4 to
use 'ordinary' operators in an overloaded context.  Something like:

  INT64 (2L * n / 3L)

The INT64(expr) macro would inspect the AST of expr and change + ->
Int64.add etc.  Of course one can do this using the pa_openin macro
and a module which overrides (+) etc, but maybe this is better?  I was
going to try modifying parts of virt-df to use this syntax to see if
it would be beneficial.

After writing virt-df which uses mixed int64, int32, int and int63[*]
types I'm starting to come around to Jon's opinion that some limited
overloading or type classes or whatever would be worthwhile.


[*] int63 is my own type: It turns into an efficient int on 64 bit
platforms, and is emulated on (now rare) 32 bit platforms.  It is
necessary for virt-df because we want ints which can comfortably hold
the size (in bytes / sectors / blocks / etc) of a block device.  You
don't really need a 64 bit int for this, but you do need something
which is bigger than 32 bits.

Richard Jones
Red Hat