O(3p) Perl Programmers Reference Guide O(3p)NAMEO - Generic interface to Perl Compiler backends
SYNOPSIS
perl -MO=[-q,]Backend[,OPTIONS] foo.pl
DESCRIPTION
This is the module that is used as a frontend to the Perl
Compiler.
If you pass the "-q" option to the module, then the STDOUT
filehandle will be redirected into the variable
$O::BEGIN_output during compilation. This has the effect
that any output printed to STDOUT by BEGIN blocks or use'd
modules will be stored in this variable rather than printed.
It's useful with those backends which produce output them-
selves ("Deparse", "Concise" etc), so that their output is
not confused with that generated by the code being compiled.
The "-qq" option behaves like "-q", except that it also
closes STDERR after deparsing has finished. This suppresses
the "Syntax OK" message normally produced by perl.
CONVENTIONS
Most compiler backends use the following conventions:
OPTIONS consists of a comma-separated list of words (no
white-space). The "-v" option usually puts the backend into
verbose mode. The "-ofile" option generates output to file
instead of stdout. The "-D" option followed by various
letters turns on various internal debugging flags. See the
documentation for the desired backend (named "B::Backend"
for the example above) to find out about that backend.
IMPLEMENTATION
This section is only necessary for those who want to write a
compiler backend module that can be used via this module.
The command-line mentioned in the SYNOPSIS section
corresponds to the Perl code
use O ("Backend", OPTIONS);
The "import" function which that calls loads in the
appropriate "B::Backend" module and calls the "compile"
function in that package, passing it OPTIONS. That function
is expected to return a sub reference which we'll call CALL-
BACK. Next, the "compile-only" flag is switched on
(equivalent to the command-line option "-c") and a CHECK
block is registered which calls CALLBACK. Thus the main Perl
program mentioned on the command-line is read in, parsed and
compiled into internal syntax tree form. Since the "-c" flag
is set, the program does not start running (excepting BEGIN
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blocks of course) but the CALLBACK function registered by
the compiler backend is called.
In summary, a compiler backend module should be called
"B::Foo" for some foo and live in the appropriate directory
for that name. It should define a function called "compile".
When the user types
perl -MO=Foo,OPTIONS foo.pl
that function is called and is passed those OPTIONS (split
on commas). It should return a sub ref to the main compila-
tion function. After the user's program is loaded and
parsed, that returned sub ref is invoked which can then go
ahead and do the compilation, usually by making use of the
"B" module's functionality.
BUGS
The "-q" and "-qq" options don't work correctly if perl
isn't compiled with PerlIO support : STDOUT will be closed
instead of being redirected to $O::BEGIN_output.
AUTHOR
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
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