I asked this just b/c I want to do matrix calculation in perl. I found under some conditions a recursion is more effective.
Thanks everybody. On 2017/3/29 23:31, Chas. Owens wrote:
On Tue, Mar 28, 2017 at 9:27 PM PYH <p...@vodafonemail.de <mailto:p...@vodafonemail.de>> wrote: Hi, what's the better way to write a recursion in perl's class? sub my_recursion { my $self = shift; .... if (...) { $self->my_recursion; } } this one? Define better. In general that is the right form (assuming there is some side effect to calling my_recursion that will cause the if statement to be false). If your function is tail recursive and it has the potential to be deeply nested, then you can take advantage of a quirk of goto to make it faster and use less memory: #!/usr/bin/perl use strict; use warnings; { package A; sub new { bless {}, shift } sub recur { my ($self, $n) = @_; return "recur done" if $n <= 0; return $self->recur($n - 1); } sub tail_recur { my ($self, $n) = @_; return "tail_recur done" if $n <= 0; @_ = ($self, $n - 1); goto &tail_recur; } } my $o = A->new; print $o->recur(1_000_000), "\n"; print $o->tail_recur(1_000_000), "\n"; NOTE: this only works if the code is tail recursive. That is, the recursive function does nothing but return the next call's return value. It works by replacing the function with itself rather than pushing another copy of the function on the stack.
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