Re: [Caml-list] (int * int) <> int*int ?

[Brian Hurt <bhurt@spnz.org>]

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On Thu, 23 Feb 2006, Frédéric Gava wrote:

>> # type t=A of int*int and  t'= B of (int*int);;
>> type t = A of int * int
>> and t' = B of (int * int)
>> See section 18.3.4 of the manual -- the distinction allows the runtime
>> representation of t to avoid a level of indirection.
>
> Thanks for your anwser but I am not convinced that is a good reason. If "t"
> is better why " t' " is not automatically tranform into "t" (it is easy, you
> just delete the global parens). ok (int->int)->int <> int->int->int or
> int*int*int<>int*(int*int) . Morever I think that int*int=(int*int)
> "everywhere" in ML...

This isn't correct- the same problem shows up in the difference between:
int*int*int and int*(int*int)- i.e. the difference between (1,2,3) and 
(1,(2,3)).  In the first case (in both examples) I have a three element 
tuple, in the second case I have a two element tuple whose second element 
is also a two element tuple (and thus I have the layer of indirection).

Also, sometimes I want one and sometimes I want the other.  I can often 
save copying information (and storing the duplicate information) if I can 
add the level of indirection- this is important if I'm copying the 
information a lot.  On the other hand, if the information isn't being 
duplicated a lot, then I can save memory by not having the extra level of 
indirection.

Brian