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use warnings;
use List::Util;
my $reduced = List::Util::reduce { $a + $b } 1, 2, 3, 4;
print "$reduced\n";

Name "main::a" used only once: possible typo at mytest.pl line 3.
Name "main::b" used only once: possible typo at mytest.pl line 3.
10

use warnings;
my @sorted = sort { $a <=> $b } 1, 2, 3, 4;
print "@sorted\n";

1 2 3 4

STATIC void
S_simplify_sort(pTHX_ OP *o)
...
    GvMULTI_on(gv_fetchpvs("a", GV_ADD|GV_NOTQUAL, SVt_PV));
    GvMULTI_on(gv_fetchpvs("b", GV_ADD|GV_NOTQUAL, SVt_PV));
    ...

void
reduce(block,...)
...
    agv = gv_fetchpv("a", GV_ADD, SVt_PV);
    bgv = gv_fetchpv("b", GV_ADD, SVt_PV);
    ...

agv = gv_fetchpv("a", GV_ADD, SVt_PV);
GvMULTI_on(agv); /* No apparent effect. */

agv = gv_fetchpv("a", GV_ADD|GV_ADDMULTI, SVt_PV); /* Nope */
agv = gv_fetchpv("a", GV_ADDMULTI, SVt_PV); /* *sigh* No. */