[m-dev.] for review: tuples [1]

[Simon Taylor]

> On Wed, Aug 02, 2000 at 12:00:38PM +1000, Fergus Henderson wrote:
> > One possibility would be to add list-like features for tuples.
> > The type `{ T1 | T2 }' could denote a tuple type whose first
> > element has type T1 and whose remainder has type T2 (which must
> > be a tuple type).
> 
> Hang on.  If you're going to do that, wouldn't you be a lot better off using
> the defn:
> 
> 	:- type (T1,T2) ---> (T1,T2)
> 
> This has several advantages over the {...} notation:
> 
>     1)  No need to introduce Fergus' {T1 | T2} notation:  (T1,T2) covers it
> 
>     2)  Much more orthodox notation mathematically (Using parentheses for
> 	tuples is only a little less common than angle brackets; they're
> 	certainly a *lot* more orthodox than braces).

Not using parentheses was a deliberate decision so that unary tuples work
when passed to a predicate which takes a polymorphic argument which is
expected to be a tuple of any arity. If unary tuples don't work, then the
arity needs to be passed separately so that the unary case can be handled
as a special case.

>     3)  Doesn't take away the orthodox notation for sets.  It would be nice to
>         reserve braces for sets at some later time.

I can't see this being useful. list_to_set([1, 2, 3]) is not that
much worse than {1, 2, 3}.
 
Simon.
--------------------------------------------------------------------------
mercury-developers mailing list
Post messages to:       mercury-developers at cs.mu.oz.au
Administrative Queries: owner-mercury-developers at cs.mu.oz.au
Subscriptions:          mercury-developers-request at cs.mu.oz.au
--------------------------------------------------------------------------