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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 we 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, 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

This is just a list of people who have submitted patches to the
module. To find someone to actually maintain this, please 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

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