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B::BUtils(3)	      User Contributed Perl Documentation	  B::BUtils(3)

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.

perl v5.14.1			  2011-06-20			  B::BUtils(3)
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