On Wed, Dec 10, 2003 at 11:44:15PM -0500, Joe Gottman wrote:
: In Perl 6, how will it be possible to iterate through two arrays at the
: same time? According to Apocalypse 4, the syntax is
: for @a; @b -> $a; $b {
:
: According to the book "Perl 6 Essentials" the syntax is
: for zip(@a, @b) -> $a, $b {
:
: Which of these is right? (of course, this being Perl, both may be right).
The latter is righter.
: Whichever of these syntaxes is right, what happens when @a and @b are of
: different sizes? I can think of three possible behaviors, each with its
: potential drawbacks:
:
: 1) The loop executes min(+ @a, + @b) times, then finishes successfully.
: 2) The loop executes min(+ @a, + @b) times, then throws an exception
: because the arrays were not of the same size.
: 3) The loop executes max(+ @a, + @b) times. If @a has fewer elements
: than @b, then after @a's elements are exhausted $a is set to undef, and
: similarly if @b has fewer elements than @a.
3 is what happens. That has not changed from the Apocalypse.
: In cases 1) and 2), the problem is how to get the elements of the larger
: array that were never iterated over. Case 2) is probably better than case
: 1), because the exception that is thrown might contain information about
: which array was larger and which elements of it have yet to be examined. In
: case 3), the problem is differentiating between an undef returned because
: the arrays were of different sizes, and an undef returned because one of the
: arrays contained an undef.
In Perl 6, undef is not necessarily a unique value. It might well contain an
unthrown exception with all the information you want hidden in a property.
That being said, it's generally erroneous to rely on any undefined value
regardless of its origin.
Larry
