Re: [Caml-list] Newbie comment on constructor syntax

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> However the following works:
>> # type x  = X of (int * int);;
>> type x = X of (int * int)
>> # let c = (1, 2) in X c;;
>> - : x = X (1, 2)

> With multiple constructors per type at least, this has a different
> in-memory representation: two objects (the constructed value and a
> tuple which the value references).

Of course, SML (being the less pragmatic brother) does not have this
"wart" and treats "X of int * int" the same as "X of (int * int)".

But this indeed comes at the cost of a less efficient representation.
You can try to "optimize" this away, but it becomes tricky when you
start using functors where type "t" is a parameter and you have
a constructor "X of t".

IOW, there were good pragmatic reasons to introduce this "wart".
This said I think Haskell shows that using a curried constructor
nicely circumvents the problem (of course it comes at the cost of not
being able to do the equivalent of "X of t", but that doesn't seem to
be much of a problem in practice, especially for Haskell where there
are no functors anyway).


        Stefan