B::Generate(3) User Contributed Perl Documentation B::Generate(3)NAME
B::Generate - Create your own op trees.
SYNOPSIS
use B::Generate;
# Do nothing, slowly.
CHECK {
my $null = new B::OP("null",0);
my $enter = new B::OP("enter",0);
my $cop = new B::COP(0, "hiya", 0);
my $leave = new B::LISTOP("leave", 0, $enter, $null);
$leave->children(3);
$enter->sibling($cop);
$enter->next($cop);
$cop->sibling($null);
$null->next($leave);
$cop->next($leave);
# Tell Perl where to find our tree.
B::main_root($leave);
B::main_start($enter);
}
WARNING
This module will create segmentation faults if you don't know how to
use it properly. Further warning: sometimes I don't know how to use it
properly.
There are lots of other methods and utility functions, but they are not
documented here. This is deliberate, rather than just through laziness.
You are expected to have read the Perl and XS sources to this module
before attempting to do anything with it.
Patches welcome.
DESCRIPTION
The "B" module allows you to examine the Perl op tree at runtime, in
Perl space; it's the basis of the Perl compiler. But what it doesn't
let you do is manipulate that op tree: it won't let you create new ops,
or modify old ones. Now you can.
Well, if you're intimately familiar with Perl's internals, you can.
"B::Generate" turns "B"'s accessor methods into get-set methods.
Hence, instead of merely saying
$op2 = $op->next;
you can now say
$op->next($op2);
to set the next op in the chain. It also adds constructor methods to
create new ops. This is where it gets really hairy.
new B::OP ( type, flags )
new B::UNOP ( type, flags, first )
new B::BINOP ( type, flags, first, last )
new B::LOGOP ( type, flags, first, other )
new B::LISTOP ( type, flags, first, last )
new B::SVOP ( type, flags, sv )
new B::COP ( flags, name, first )
In all of the above constructors, "type" is either a numeric value
representing the op type (62 is the addition operator in certain perl
versions, for instance) or the name of the op. ("add")
Incidentally, if you know about custom ops and have registed them
properly with the interpreter, you can create custom ops by name: "new
B::OP("mycustomop",0)", or whatever.
"first", "last" and "other" are ops to be attached to the current op;
these should be "B::OP" objects. If you haven't created the ops yet,
don't worry; give a false value, and fill them in later:
$x = new B::UNOP("negate", 0, undef);
# ... create some more ops ...
$x->first($y);
In addition, one may create a new "nextstate" operator with
newstate B::op ( flags, label, op)
in the same manner as "B::COP::new" - this will also, however, add the
"lineseq" op.
Finally, you can set the main root and the starting op by passing ops
to the "B::main_root" and "B::main_start" functions.
This module can obviously be used for all sorts of fun and
optimizational purposes. One example will be in conjuction with source
filters; have your source filter parse an input file in a foreign
language, create an op tree for it and get Perl to execute it. Then
email me and tell me how you did it. And why.
OTHER METHODS
B::SVOP->sv()
Returns the SV value instead of the "B::SV" object. For instance:
$b_sv = $svop->sv;
if ($b_sv->sv == 3) {
print "SVOP's SV has an IV of 3\n"
}
But to set the SV you need a proper B::SV object.
$op->dump
Runs "Perl_op_dump" on an op; this is roughly equivalent to
"B::Debug", but not quite.
$b_sv->dump
Runs "Perl_sv_dump" on an SV; this is exactly equivalent to
"Devel::Peek::dump($b_sv->sv)"
$b_op->linklist
Sets the "op_next" pointers in the tree in correct execution order,
overwriting the old "next" pointers. You need to do this once you've
created an op tree for execution, unless you've carefully threaded
it together yourself.
$b_op->scope
Create a surrounding scope for the b_op, "parenthesize" it.
Creates on OPf_PARENS (alerady parenthesized by the parser) a full
lineseq, enter, b_op, leave sequence.
Otherwise just scope, b_op.
B::SVOP->new_svrv ( type, flags, sv )
Similar to B::SVOP->new ( type, flags, sv ), it just creates a new
SVOP with an attached sv as SvRV to the given sv.
$cv->NEW_with_start (root, start)
Clone the "cv" with new root and start ops. Note that contrary to
"cv_clone", the PADLIST and pad index is kept, but the index might
point to a different lexical, because the PADLIST indices will be
different. See t/new_cv.t.
Warning: "$cv-"NEW_with_start> is disabled on some strict platforms,
like MSWin32. See CPAN RT#28912.
$b_op->targ ( [ targ] )
Get or set the PADOFFSET.
EXPORT
None.
AUTHOR
Simon Cozens, "simon@cpan.org"
MAINTAINERS
Currently maintained by Reini Urban.
This is just a list of people who have submitted patches to the module.
You may also try contacting perl5-porters.
Josh Jore, Michael Schwern, Jim Cromie, Scott Walters, Reini Urban,
Anton Berezin, Dmitry Karasik.
Maintainership permissions do have: Artur Bergman, Chia-liang Kao,
Anton Berezin, Jim Cromie, Joshua ben Jore, Michael G Schwern, Matt S
Trout, Reini Urban, Scott Walters.
LICENSE
This module is available under the same licences as perl, the Artistic
license and the GPL.
SEE ALSO
B, perlguts, op.c, perloptree with B::C
perl v5.14.2 2012-03-07 B::Generate(3)
