As near as I can tell, no built-in function listed in index-functions has a prototype (just checked) and some of these behave more normally with regards to return. For instance, both map and sort are on that list. Neither map nor sort have defined prototypes, but sort treats the return inside the block as if it were returning from a subroutine, just like my custom sub foo above.

# no compile problems here!

my @x = sort { return $a <=> $b; } (3, 2, 1);
print "sorted: (@x)\n";

#prints:  sorted (1, 2, 3)
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Best, beth

Update: Struck out incorrect portion of post - forgot to include "CORE::" in the function name, as pointed out by Anonymous Monk below.

..has a prototype (just checked)

perl -le"printf qq~%10s %s \n~, $_, prototype(qq!CORE::$_!) for @ARGV"
+ abs int push pop map grep sort stat
       abs ;$
       int ;$
      push \@@
       pop ;\@
       map
      grep
      sort
      stat *
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I did not use the "CORE::" prefix when I tested. I too get your results when I do.

In any case the main point still holds: both map and sort according to your machine (and mine) have an undefined prototype. The fact of an undefined prototype does not provide an explanation of the different behavior. I only wish it were that simple. But thanks, anyway, for your help.

Best, beth