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Combining Import and Source-Filter to implement Syntactic Macro mechanism

by LanX (Sage)
on Feb 19, 2019 at 19:21 UTC ( #1230195=perlquestion: print w/replies, xml ) Need Help??

LanX has asked for the wisdom of the Perl Monks concerning the following question:

Hi

I have the idea to use a combination of use and source filter as safe syntactic macro mechanism like in LISP.

(well a poor mans version but still better than the alternatives which try to parse Perl)

The following code injects the new code at compile time into the line after the use statement.

My problem is that statements in the same line following the use are skipped, before the insert starts.

Any idea if this can be fixed?

Probably by manipulating the DATA filehandle reading the source?

Sample code implements an inlined SWAP of two variables.

>> cat exp/t_inject.pl use lib '../lib'; my ($x,$y); BEGIN {($x,$y)=(0,42)} use Filter::Inject $x,$y; warn "after same line"; warn "+1 line"; warn "+2 line"; warn "$x $y";

Output shows variables have been swapped, but inlining happens after the lines end (not the statements end, see mark)

$ perl t_inject.pl IMPORT(Filter::Inject 0 42) at ../lib/Filter/Inject.pm line 46. after same line at t_inject.pl line 6. <--- --- START MACRO swap at t_inject.pl line 9. --- END MACRO swap at t_inject.pl line 14. +1 line at t_inject.pl line 7. +2 line at t_inject.pl line 8. 42 0 at t_inject.pl line 9.

(please note, while the inject sub is only hardcode to simplify the demonstration, the full scale version creates pseudo modules with own macros on the fly, which can be called as use swap $x,$y )

please ignore the Module-starter boilerplate

>> cat lib/Filter/Inject.pm package Filter::Inject; use 5.006; use strict; use warnings FATAL => 'all'; =head1 NAME Filter::Inject - The great new Filter::Inject! =head1 VERSION Version 0.02 =cut our $VERSION = '0.02'; =head1 SYNOPSIS Quick summary of what the module does. Perhaps a little code snippet. use Filter::Inject; my $foo = Filter::Inject->new(); ... =head1 EXPORT A list of functions that can be exported. You can delete this section if you don't export anything, such as for a purely object-oriented mod +ule. =cut package Filter::Inject ; use Filter::Util::Call ; sub import { warn "IMPORT(@_)"; my $package = shift; my $inject = inject(@_); # adjust line number to disguise injection my ($file,$line) = (caller)[1,2]; $line++; $inject .= qq{\n# line $line "$file"\n}; filter_add( sub { my $status = filter_read_exact(1); if ( $status > 0) { $_= $inject .";".$_; filter_del(); } $status ; } ) } sub inject { local $"=','; package swap; our $args = \@_; return q{ { warn "--- START MACRO swap"; package swap; our $args; my $tmp = $args->[0]; $args->[0] = $args->[1]; $args->[1] = $tmp; warn "--- END MACRO swap"; } } } 1 ; =head1 AUTHOR Rolf Michael Langsdorf, C<< <lanxperl at gmail.com> >> =head1 BUGS Please report any bugs or feature requests to C<bug-filter-inject at r +t.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue= +Filter-Inject>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes. =head1 SUPPORT You can find documentation for this module with the perldoc command. perldoc Filter::Inject You can also look for information at: =over 4 =item * RT: CPAN's request tracker (report bugs here) L<http://rt.cpan.org/NoAuth/Bugs.html?Dist=Filter-Inject> =item * AnnoCPAN: Annotated CPAN documentation L<http://annocpan.org/dist/Filter-Inject> =item * CPAN Ratings L<http://cpanratings.perl.org/d/Filter-Inject> =item * Search CPAN L<http://search.cpan.org/dist/Filter-Inject/> =back =head1 ACKNOWLEDGEMENTS =head1 LICENSE AND COPYRIGHT Copyright 2018 Rolf Michael Langsdorf. This program is free software; you can redistribute it and/or modify i +t under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at: L<http://www.perlfoundation.org/artistic_license_2_0> Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License. By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license. If your Modified Version has been derived from a Modified Version made by someone other than you, you are nevertheless required to ensure tha +t your Modified Version complies with the requirements of this license. This license does not grant you the right to use any trademark, servic +e mark, tradename, or logo of the Copyright Holder. This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import an +d otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by t +he Package. If you institute patent litigation (including a cross-claim o +r counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed. Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDE +R AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES +. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE +, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. =cut 1; # End of Filter::Inject

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

Replies are listed 'Best First'.
Re: Combining Import and Source-Filter to implement Syntactic Macro mechanism
by choroba (Archbishop) on Feb 19, 2019 at 21:04 UTC
    Very nice!

    Have you tried switching to PPI or PPR? They might solve the same line problem.

    map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
      The idea of syntactic macros is to avoid any parsing.

      This makes them so useful.

      Introducing an external parser for Perl would effectively reduce the approach to the same level of reliability like classic source filters.

      I'd rather live with that limitation.

      Edit

      Fwiw: I already tried combining this approach with Keyword::Simple, but this is hindered by an internal bug.

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

        Hey LanX,

        Sounds like you want to avoid a Perl parser within Perl here, but honestly, PPI is pretty well the only thing that can parse Perl as closely as perl itself.

        What's your true objective here? If we're avoiding certain things, what things are acceptable?

        Perhaps your end objective isn't clear. Could you elaborate?

Re: Combining Import and Source-Filter to implement Syntactic Macro mechanism
by BrowserUk (Patriarch) on Feb 19, 2019 at 23:38 UTC

    I'm not set up to test the idea; but would wrapping a bare block or BEGIN block around the use force perl to see the rest of the insert?


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      If you mean that, then no:
      {use Filter::Inject $x,$y;} print "after same line (x=$x, y=$y)\n"; print "new line: x=$x, $y\n";
      BEGIN {use Filter::Inject $x,$y;} print "after same line (x=$x, y=$y)\ +n"; print "new line: x=$x, $y\n";

      or even that:

      BEGIN {use Filter::Inject $x,$y;};;; print "after same line (x=$x, y=$ +y)\n"; print "new line: x=$x, $y\n";
      Not sure what you mean.

      Example?

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

Re: Combining Import and Source-Filter to implement Syntactic Macro mechanism
by bliako (Monsignor) on Feb 20, 2019 at 01:10 UTC

    Maybe a look at https://metacpan.org/source/RURBAN/Filter-1.59/Call/Call.xs can be helpful? If one gets passed all those cryptic macros. One can start by clarifying where that points:

    out_ptr = SvPVX(my_sv) + BUF_OFFSET(my_sv) ;

    and also: ninstr(out_ptr, out_ptr + n, nl, nl + 1)) which is looking for a needle = nl = "\n0" in the big haystack=out_ptr according to perlapi

      Unfortunately reading the source code is more of a guessing game for me.

      But I'm pretty sure that's just the way it is, the registered filter will only kick in for the next line. (Which could lead to weird bugs, if the same line statement spans multiple lines)

      I was hoping to discuss it with Reini at the German Perl Workshop, but he's still missing among the attendants yet.

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

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