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perlman:B::Deparse

by root (Scribe)
on Dec 23, 1999 at 00:50 UTC ( #1158=perlfunc: print w/ replies, xml ) Need Help??

B::Deparse

See the current Perl documentation for B::Deparse.

Here is our local, out-dated (pre-5.6) version:


B::Deparse - Perl compiler backend to produce perl code



perl -MO=Deparse[,-uPACKAGE][,-p][,-l][,-sLETTERS] prog.pl



B::Deparse is a backend module for the Perl compiler that generates perl source code, based on the internal compiled structure that perl itself creates after parsing a program. The output of B::Deparse won't be exactly the same as the original source, since perl doesn't keep track of comments or whitespace, and there isn't a one-to-one correspondence between perl's syntactical constructions and their compiled form, but it will often be close. When you use the -p option, the output also includes parentheses even when they are not required by precedence, which can make it easy to see if perl is parsing your expressions the way you intended.

Please note that this module is mainly new and untested code and is still under development, so it may change in the future.


OPTIONS

As with all compiler backend options, these must follow directly after the '-MO=Deparse', separated by a comma but not any white space.

-p

Print extra parentheses. Without this option, B::Deparse includes parentheses in its output only when they are needed, based on the structure of your program. With -p, it uses parentheses (almost) whenever they would be legal. This can be useful if you are used to LISP, or if you want to see how perl parses your input. If you say

    if ($var & 0x7f == 65) {print "Gimme an A!"} 
    print ($which ? $a : $b), "\n";
    $name = $ENV{USER} or "Bob";

B::Deparse,-p will print

    if (($var & 0)) {
        print('Gimme an A!')
    };
    (print(($which ? $a : $b)), '???');
    (($name = $ENV{'USER'}) or '???')

which probably isn't what you intended (the '???' is a sign that perl optimized away a constant value).

-uPACKAGE

Normally, B::Deparse deparses the main code of a program, all the subs called by the main program (and all the subs called by them, recursively), and any other subs in the main:: package. To include subs in other packages that aren't called directly, such as AUTOLOAD, DESTROY, other subs called automatically by perl, and methods, which aren't resolved to subs until runtime, use the -u option. The argument to -u is the name of a package, and should follow directly after the 'u'. Multiple -u options may be given, separated by commas. Note that unlike some other backends, B::Deparse doesn't (yet) try to guess automatically when -u is needed -- you must invoke it yourself.

-l

Add '#line' declarations to the output based on the line and file locations of the original code.

-sLETTERS

Tweak the style of B::Deparse's output. At the moment, only one style option is implemented:
C

Cuddle elsif, else, and continue blocks. For example, print

    if (...) {
         ...
    } else {
         ...
    }

instead of

    if (...) {
         ...
    }
    else {
         ...
    }

The default is not to cuddle.


BUGS

See the 'to do' list at the beginning of the module file.


AUTHOR

Stephen McCamant <alias@mcs.com>, based on an earlier version by Malcolm Beattie <mbeattie@sable.ox.ac.uk>


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