NAME

       B::Utils - Helper functions for op tree manipulation

SYNOPSIS

         use B::Utils;

DESCRIPTION

       These functions make it easier to manipulate the op tree.

FUNCTIONS

       "all_starts"
       "all_roots"
          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 "__MAIN__".

          Note: Certain "dangerous" stashes are not scanned for subroutines: the list of such
          stashes can be found in @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 "B" and "B::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 { ... };

          the subroutine will not appear in the hash. This is just as well, since they're
          anonymous... If you want to get at them, use...

       "anon_subs()"
          This returns an array of hash references. Each element has the keys "start" and "root".
          These are the starting and root ops of all of the anonymous subroutines in the program.

       "$op->oldname"
          Returns the name of the op, even if it is currently optimized to null.  This helps you
          understand the stucture of the op tree.

       "$op->kids"
          Returns an array of all this op's non-null children, in order.

       "$op->first"
       "$op->last"
       "$op->other"
          Normally if you call first, last or other on anything which is not an UNOP, BINOP or
          LOGOP respectivly it will die.  This leads to lots of code like:

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

          B::Utils provides every op with first, last and other methods which will simply return
          nothing if it isn't relevent.

       "$op->parent"
          Returns the parent node in the op tree, if possible. Currently "possible" means "if the
          tree has already been optimized"; that is, if we're during a "CHECK" block. (and hence,
          if we have valid "next" pointers.)

          In the future, it may be possible to search for the parent before we have the "next"
          pointers in place, but it'll take me a while to figure out how to do that.

       "$op->previous"
          Like "$op->next", but not quite.

       walkoptree_simple($op, \&callback, [$data])
          The "B" module provides various functions to walk the op tree, but they're all rather
          difficult to use, requiring you to inject methods into the "B::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 $data as the second.

          All the "walk" functions set $B::Utils::file and $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 "walkoptree_simple", but will only call the callback if the
          "filter" returns true. The "filter" is passed the op in question as a parameter; the
          "opgrep" function is fantastic for building your own filters.

       walkallops_simple(\&callback, [$data])
          This combines "walkoptree_simple" with "all_roots" and "anon_subs" to examine every op
          in the program. $B::Utils::sub is set to the subroutine name if you're in a subroutine,
          "__MAIN__" if you're in the main program and "__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.

       opgrep(\%conditions, @ops)
          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": "["!"]")

          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

   EXPORT
       None by default.

AUTHOR

       Simon Cozens, "simon@cpan.org"

TODO

       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.

SEE ALSO

       B, B::Generate.