Re: how can i hold temporary values in a recursive function

Several ways:

Simple closure:

{
   my %state;
   sub recursive {
       my $arg = shift;
       ...
       if( ( $arg = $state{ $arg } ) == ... ) {
            return recursive( $arg );
       else {
            return 0
       }
   }
}
[download]

Closure via helper function:

sub rec_helper {
    my %state;
    my $recursive;
    $recursive = sub {
        my( $arg ) = shift;
        ...
        if( ( $arg = $state{ $arg ) ) == ... ) {
             return $recursive->( $arg );
        }
        else {
             return 0;
        }
    };
}
[download]

State passed through args (often via helper function ):

sub recursive {
    my( $state, $arg ) = @_;
    ...
    if( ( $arg = $state->{ $arg } ) == ... ) {
         return recursive( $state, $arg );
    }
    else {
         return 0;
    }
}

sub rec_helper{
    my $arg = shift;
    my %state;
    return recursive( \%state, $arg );
}
[download]

And many variations on those themes.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

RIP an inspiration; A true Folk's Guy

Comment on Re: how can i hold temporary values in a recursive function Select or Download Code

Replies are listed 'Best First'.
Re^2: how can i hold temporary values in a recursive function by ikegami (Patriarch) on Apr 18, 2010 at 21:04 UTC
#2 leaks memory every time you call `rec_helper`. The sub you create references $recursive which references the sub, so you have a memory cycle. The simplest solution is to avoid using a lexical to hold the reference to the sub. It even simplifies the code a little. `sub rec_helper { my %state; local *recursive = sub { my( $arg ) = shift; ... if( ( $arg = $state{ $arg ) ) == ... ) { return recursive( $arg ); } else { return 0; } }; }` [download]	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re^2: how can i hold temporary values in a recursive function
by ikegami (Patriarch) on Apr 18, 2010 at 21:04 UTC

rec_helper

sub rec_helper {
    my %state;
    local *recursive = sub {
        my( $arg ) = shift;
        ...
        if( ( $arg = $state{ $arg ) ) == ... ) {
             return recursive( $arg );
        }
        else {
             return 0;
        }
    };
}
[download]

[reply]
[d/l]
[select]