Jim Cromie wrote:
> with p5, Ive often written
>
> eval {} or carp "$@ blah";
>
> it seems to work,
....modulo any block that returns false :-(
> and it reads nicer (to my eye) than
>
> eval {}; if ($@) {}
>
> but I surmise that it works cuz the return-value from the block is non-zero,
> for successful eval, and 0 or undef when block dies, not cuz of magical
> treatment of $@.
No. C<eval> return the last evaluated value in the block, unless an
exception is thrown, in which case it returns C<undef>. The problem with
the C<eval {...} or whatever> approach is that there are situations in
which the block can evaluate successfully but still return C<undef>.
On failure, C<eval> sets C<$@>, so careful programmers test it separately.
Of course, you *can* do that in a single statment if you want:
eval {} or @! and carp "$@ blah";
> I gather that ';' is unneeded in p6,
Err...no.
> and given that $! is the 'exception'al topicalizer,
Only inside an explicit CATCH block.
> is this construct no longer reliant on the last value in the eval block ?
In Perl 6 C<eval BLOCK> becomes C<try BLOCK> and you'll still be able to write:
try { ... } // carp $!;
but that will trip up if the final value of the C<try> block is C<undef>.
What you want is:
try {
...
CATCH { carp $! }
}
> put another way, does the 'topicalizer' reflect the exit condition of
> the closure ?
Only in a CATCH block.
Damian
