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[Caml-list] Constructors as functions and tuples in constructors
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Date: 2003-10-09 (12:44)
From: Andreas Rossberg <rossberg@p...>
Subject: Re: [Caml-list] Constructors as functions and tuples in constructors
Dan Grossman wrote:
> (1) A pattern-match would have the potential of allocating memory, which 
> some may judge poorly.  But the compiler could warn about this.

Good point, but I don't think anybody would really care.

> (2) This transformation does require the type A carries is transparent. 
>  So we still couldn't relax the "other" restriction that a signature 
> cannot hide an unparenthesized t1 * t2 variant.

Of course, no change there.

> (3) It's not clear how far this trivial transformation should be 
> generalized.  For example, given
>   type t = A of int * int * int * int
> which of these should we allow
>   A(1,2,3,4)
>   A((1,2,3,4))
>   A((1,2),(3,4))
>   A(1,(2,3),4)
>   ...

Not sure what your getting at. OCaml makes otherwise redundant 
parentheses around constructor argument types significant. That is a 
hack to allow for a more efficient representation. The idea is to make 
that hack as transparent as possible.

But that aim of course is unrelated to changing the meaning of the 
multifix type operator * itself. So the first two of your examples 
should certainly be legal (and they are already), while the others 
should not, no more than

   ((1,2),(3,4)) : int * int * int * int  (* eek! *)
   (1,(2,3),4) : int * int * int * int   (* ouch! *)

- Andreas

Andreas Rossberg,

"Computer games don't affect kids; I mean if Pac Man affected us
  as kids, we would all be running around in darkened rooms, munching
  magic pills, and listening to repetitive electronic music."
  - Kristian Wilson, Nintendo Inc.

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