I have no problem with a helper function having more arguments.
sub fact {
my ($n) = @_;
local *_fact = sub {
my ($n, $prod) = @_;
return $prod if $n == 0;
return _fact($n-1, $n*$prod);
};
return _fact($n, 1);
}
fact($n);
In this case, you could even fake it as follows:
sub fact {
my ($n, $prod) = @_;
$prod ||= 1;
return $prod if $n == 0;
return _fact($n-1, $n*$prod);
}
fact($n);
But since Perl doesn't do tail recursion optimisation, and since sub calls are relatively slow, you're better off with:
sub fact {
my ($n) = @_;
my $prod = 1;
$prod *= $n-- while $n > 0;
return $prod;
}
fact($n);
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