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Date: Tue, 7 Nov 2000 14:28:30 +0100
To: Chris Hecker <checker@d6.com>
Cc: caml-list@inria.fr
Subject: Re: fixed length arrays as types
Message-ID: <20001107142830.B30034@lambda.u-strasbg.fr>
References: <4.3.2.7.2.20001104165041.00b3e370@shell16.ba.best.com>
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In-Reply-To: <4.3.2.7.2.20001104165041.00b3e370@shell16.ba.best.com>; from checker@d6.com on Sat, Nov 04, 2000 at 07:06:35PM -0800
From: Sven LUTHER <luther@dpt-info.u-strasbg.fr>
Sender: weis@pauillac.inria.fr

On Sat, Nov 04, 2000 at 07:06:35PM -0800, Chris Hecker wrote:
> 
> Is there any way to do this:
> 
> type vector3 = [| float; float; float |];
> 
> Basically, I want an array of a given length to be a given type, so I can use the type system to check add_vector3 rather than throwing if the arrays don't match.  I know I can make records {x:float, y:float} but I'd like it to be parameterizable at compile time.
> 
> Something like this C++:
> 
> template <int unsigned N> class vector { float a[N]; };
> vector<3> add( vector<3> v1, vector<3> v2 );
> 
> vector<3> v3 = add(vector<3>(),vector<3>());    // works
> vector<3> v4 = add(vector<5>(),vector<3>());    // type error (note v<5>
> 
> I guess the higher level question is whether scalar constants can be part of the type signature like they can be in C++.  Or, the related but different question is whether there's a way to differentiate between "float a[]" (or "float *a"), the variable length array type, and "float a[3]", a fixed length array type, which C++ doesn't do, but it lets you wrap the ideas in template classes which do allow you to represent this to the type system.

Try using lists, 

Friendly,

Sven Luther