[m-rev.] for review: arrays and the debugger

[Zoltan Somogyi]

I wrote:
> library/std_util.m:
> 	Add a new predicate, limited_deconstruct, which usually does what
> 	deconstruct does, but fails (and does not allocate any memory) if
> 	the arity of the supplied term is beyond a given limit.

On 16-Jun-2001, Fergus Henderson <fjh at cs.mu.OZ.AU> wrote:
> Why not just use functor/3 to test the arity,
> and then call deconstruct/4 or not depending on the arity returned by
> fnuctor/3?

Performance. Doing that would require interpreting the RTTI structures twice.
For discriminated union types, one of the most common data structures, that is
reasonably expensive. The extremely small risk of bumping into the limit is not
worth it.

One of Henry Spencer's proverbs puts it this way: "carrying a net before you
in case you trip is usually wasted effort".

Zoltan.
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