Re: [Caml-list] ocaml and named constants

[Luc Maranget <Luc.Maranget@inria.fr>]

> 
> On Tue, 29 May 2001, Luc Maranget wrote:
> > > 
> > > 	Is there any semantic reason why
> > > one cannot use variables, or even expressions? Apart from
> > > the obvious syntactic problem.
> > 
> > Not that obvious, I think this would make pattern-matching look
> > like even more complicated.
> > It is good to stress on the fact that
> > in match .. with p ->, p is a pattern
> >   1. Some value ``whith holes''
> >   2. Something we programmer and compiler know without any computation.
> 
> I read a paper on an SML extension to handle this named constant problem,
> here at ftp://ftp.research.bell-labs.com/dist/smlnj/papers/92-tr-aitken.ps
> Anyone know why this or some similar approach hasn't caught on? The CamlP4 
> approach isn't too bad, but this seems important enough to be in the core 
> language. 
> 
> This is certainly on my "wish list" for future enhancements, since there
> are so many cases where named constants are useful and the current
> workarounds are a bit ugly. 
> 
> -- Brian
> 
> 
I got the reference and the idea (I think).

These are the so-called ``macros (that work!)''
They give you
  1- Mandatory optimizations (aka inlining)
  2- A different syntax for function and constructor application
     both in patterns.

Stuff for making all that cross module boundaries (allowing data
abstraction and pattern-matching to cohabit) looks a bit
complicated and may not be what you want.

But I have another remark
as far a ``manifest constants'' are the issue, Polymorphic
variants
(http://caml.inria.fr/ocaml/htmlman/manual003.html)
seem to do the job.

After all, provided you do not care much about the actual value of Foo)
you can write :

match x with
| `Foo -> ...
| `Bar -> ...
| _    -> ...

In place of

const Foo = 0
const Bar = 1

match x with
| Foo -> ...
| Bar -> ...
| _   -> ...



--Luc
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