How does your favorite language handle deep recursion? [closed]

Answer 1

There is a way to improve upon the Perl code, to make it use a constant size stack. You do this by using a special form of goto.

sub f{
  if( $_[0] < $_[1] ){

    # return f( $_[0]+1, $_[1] );

    @_ = ( $_[0]+1, $_[1] );
    goto &f;

  } else {
    return $_[0]
  }
}

When first called it will allocate space on the stack. Then it will change its arguments, and restart the subroutine, without adding anything more to the stack. It will therefore pretend that it never called its self, changing it into an iterative process.

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You could also use the Sub::Call::Recur module. Which makes the code easier to understand, and shorter.

use Sub::Call::Recur;
sub f{
  recur( $_[0]+1, $_[1] ) if $_[0] < $_[1];
  return $_[0];
}