The expensive recursion can be optimized away. Also, you might also want to specify the "&" prototype to also allow map-like syntax.
sub scanl(&@) {
my ($f, @rv) = @_;
$rv[$_] = $f->($rv[$_-1], $rv[$_])
for 1..$#rv;
return @rv;
}
my @rv = scanl \÷, 64, 4,2,4;
-or-
my @rv = scanl { $_[0] / $_[1] } 64, 4,2,4;
Finally, you could use $a and $b instead of $_[0] and $_[1], but that would prevent the use of existing functions directly. If that's not a problem, using $a and $b can be done by assigning references to *$ap and *$bp after doing
my $pkg = caller();
my $ap = do { no strict 'refs'; \*{$pkg.'::a'} }; local *$ap;
my $bp = do { no strict 'refs'; \*{$pkg.'::b'} }; local *$bp;
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