[mercury-users] maybe(T)

[Fergus Henderson]

On 20-Oct-2002, Michael Day <mikeday at yeslogic.com> wrote:
> 
> :- type maybe(T)
> 	--->	yes(T)
> 	;	no.
> 
> On the C backends, is this type implemented by using a pointer to T to
> represent yes(T) and NULL to represent no?
> If not, is it implemented using an equally efficient strategy?

Yes.  Well, close enough anyway.  We use a pointer to T to represent
yes(T) and we use a pointer with value "1" to represent no.

For the MLDS back-ends, if you use the right compilation options then
we do in fact use exactly the representation that you describe, but
currently this is not the default.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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