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Octocat-spinner-32 Generate.xs
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README
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
    Malcolm Beattie's "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::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, 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 purposes. The
    best one 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_sv->sv
       Returns a real SV instead of a "B::SV". For instance:

           $b_sv = $svop->sv;
           if ($b_sv->sv == 3) {
               print "SVOP's SV has an IV of 3\n"
           }

       You can't use this to set the SV. That would be scary.

    $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.

    $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 MSWin32, see CPAN
       RT#28912.

    $b_op->targ ( [ targ] )
       Get or set the PADOFFSET.

       Warning: Setting the targ with "$op-"targ> is disabled on MSWin32,
       see CPAN RT#28912.

  EXPORT
    None.

AUTHOR
    Simon Cozens, "simon@cpan.org" (Who else?)

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

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