B::Utils - Helper functions for op tree manipulation

  use B::Utils;

These functions make it easier to manipulate the op tree.

Returns a hash of all of the starting ops or root ops of optrees, keyed to subroutine name; the optree for main program is simply keyed to CW__MAIN__. Note: Certain dangerous stashes are not scanned for subroutines: the list of such stashes can be found in CW@B::Utils::bad_stashes. Feel free to examine and/or modify this to suit your needs. The intention is that a simple program which uses no modules other than CWB and CWB::Utils would show no addition symbols. This does not return the details of ops in anonymous subroutines compiled at compile time. For instance, given

    $a = sub { ... };

    $op->first if $op->can('first');

walkoptree_simple($op, \&callback, [$data])

The CWB module provides various functions to walk the op tree, but they're all rather difficult to use, requiring you to inject methods into the CWB::OP class. This is a very simple op tree walker with more expected semantics. The &callback is called at each op with the op itself passed in as the first argument and any additional CW$data as the second. All the CWwalk functions set CW$B::Utils::file and CW$B::Utils::line to the appropriate values of file and line number in the program being examined. Since only COPs contain this information it may be unavailable in the first few callback calls.

walkoptree_filtered($op, \&filter, \&callback, [$data])

This is much the same as CWwalkoptree_simple, but will only call the callback if the CWfilter returns true. The CWfilter is passed the op in question as a parameter; the CWopgrep function is fantastic for building your own filters.

walkallops_simple(\&callback, [$data])

This combines CWwalkoptree_simple with CWall_roots and CWanon_subs to examine every op in the program. CW$B::Utils::sub is set to the subroutine name if you're in a subroutine, CW__MAIN__ if you're in the main program and CW__ANON__ if you're in an anonymous subroutine.

walkallops_filtered(\&filter, \&callback, [$data])

Same as above, but filtered.

carp(@args)

croak(@args)

Warn and die, respectively, from the perspective of the position of the op in the program. Sounds complicated, but it's exactly the kind of error reporting you expect when you're grovelling through an op tree. Returns the ops which meet the given conditions. The conditions should be specified like this:

    @barewords = opgrep(
                        { name => "const", private => OPpCONST_BARE },
                        @ops
                       );

You can specify alternation by giving an arrayref of values:

    @svs = opgrep ( { name => ["padsv", "gvsv"] }, @ops)

And you can specify inversion by making the first element of the arrayref a !. (Hint: if you want to say anything, say not nothing: CW["!"]) You may also specify the conditions to be matched in nearby ops.

    walkallops_filtered(
        sub { opgrep( {name => "exec", 
                       next => {
                                 name    => "nextstate",
                                 sibling => { name => [qw(! exit warn die)] }
                               }
                      }, @_)},
        sub { 
              carp("Statement unlikely to be reached"); 
              carp("\t(Maybe you meant system() when you said exec()?)\n");
        }
    )

Get that? Here are the things that can be tested:

        name targ type seq flags private pmflags pmpermflags
        first other last sibling next pmreplroot pmreplstart pmnext

None by default.

Simon Cozens, CWsimon@cpan.org

I need to add more Fun Things, and possibly clean up some parts where the (previous/parent) algorithm has catastrophic cases, but it's more important to get this out right now than get it right.

B, B::Generate.