NAME

Acme::Pythonic - Python whitespace conventions for Perl

SYNOPSIS

 use Acme::Pythonic; # this semicolon yet needed

 sub exp_mod:
     use integer
     my ($i, $j, $n) = @_
     my $r = 1
     while $j:
         if $j % 2:
             $r = ($i*$r) % $n
         $j >>= 1
         $i = ($i**2) % $n
     return $r

DESCRIPTION

Acme::Pythonic is a source filter that brings Python whitespace conventions to Perl.

This module is thought for those who embrace contradictions. A humble aid for walkers of the Whitespace Matters Way in their pursuit of highest realization, only attained with SuperPython.

DETAILS

Labels

This is the Acme::Pythonic version of the example in perlsyn:

    OUTER: for my $wid in @ary1:
        INNER: for my $jet in @ary2:
            next OUTER if $wid > $jet
            $wid += $jet

Labeled blocks work as well:

    my $k = 7
    FOO:
        --$k
        last FOO if $k < 0
        redo FOO

Note that if we put a label in the line before in a control structure indentation matters. This would be a non-equivalent reformat of the example above:

    OUTER:
        for my $wid in @ary1:               # NOT WHAT WE WANT
            INNER:
            for my $jet in @ary2:           # GOOD, ALIGNED
                next OUTER if $wid > $jet
                $wid += $jet

Since the first for is indented with respect to OUTER: we get a labeled block containing a for loop, instead of a labeled for.

Labels can be composed just of upper-case letters. That was decided so that list operators can be chained:

    my @st = map:
        $_->[0]
    sort:
        $a->[1] <=> $b->[1]
    map:
        [$_, $foo{$_}]
    keys %foo

and &-prototyped subroutines can be used like this:

    sub mygrep (&@):
        my $code = shift
        my @result
        foreach @_:
            push @result, $_ if &$code
        return @result

    @array = mygrep:
        my $aux = $_
        $aux *= 3
        $aux += 1
        $aux % 2
    reverse 0..5

Nevertheless support for this has to be improved, see LIMITATIONS.

do/while-like constructs

Acme::Pythonic tries to detect loop modifiers after a do BLOCK. Thus

    do:
        do_something()
        do_something_else()
    while $condition

is seen as a do/while, whereas

    do:
        do_something()
        do_something_else()
    while $condition:
        handle_some_stuff()

is not.

New Keywords

pass

To be able to have an empty block we provide pass:

    sub abstract_method:
        pass

in

This works:

    foreach my $foo @array:
        do_something_with $foo

However in is supported in case you find the following more readable

    foreach my $foo in @array:
        do_something_with $foo

This keyword can be used if there's no variable to its left too, which means we are dealing with $_ as usual:

    foreach in @array:
        s/foo/bar/

but can't be used when the loop acts as a modifier:

    print foreach in @array # ERROR

Continuation lines

As in Python, you can break a logical line in several physical lines using a backslash at the end:

    my $total = total_products() + \
                total_delivery() + \
                total_taxes()

and in that case the indentation of those additional lines is irrelevant.

Unlike Python, we ignore backslashes that end a line in a comment:

    my $a = 1  # this comment ends in a backslash, no problem \

There's no technical reason for this, only it does not belong to the whitespace conventions we are trying to mimick.

Ending commas

If a line ends in a comma or arrow (=>) it is conceptually joined with the following:

    my %authors = (Perl   => "Larry Wall",
                   Python => "Guido van Rossum")

As in Python, comments can be intermixed there:

    my %hello = (Catalan => 'Hola',  # my mother tongue
                 English => 'Hello)

LIMITATIONS

Keywords followed by code in the same line are not supported. This would be valid in Python:

    if $n % 2: $n = 3*$n + 1
    else: $n /= 2

but it does not work in Acme::Pythonic. The reason for this is that it would be hard to identify the colon that closes the expression without parsing Perl, consider for instance:

    if keys %foo::bar ? keys %main:: : keys %foo::: print "foo\n"

On the other hand, to use a subroutine with prototype (&) you need to add the trailing semicolon in its own line by now:

    sub foo (&):
        pass

    foo:
        pass
    ;

That's a pity, improving this is in the TODO list.

DEBUG

You can pass a debug flag to Acme::Pythonic like this:

    use Acme::Pythonic debug => 1;

In debug mode the module prints to standard output the code it has generated and substitutes everything with a dummy 1;, so nothing gets executed. This way the resulting source can be inspected.

The module tries to generate human readable code following perlstyle. Blank lines and comments are preserved.

This happens before Filter::Simple undoes the blanking out of PODs, strings, and regexps. Thus, those parts will be seen as $;s in a row ($; is \034 by default.)

BUGS

This module uses a regexp approach and the superb help of Filter::Simple. The regexp part of this means it is broken from the start, though I've tried hard to make it as robust as I could. Bug reports will be very welcome, just drop me a line!

THANKS

Damian Conway gave his full blessing if I wanted to write a module like this based on his unpublished Language::Pythonesque. The code that handles indentation is inspired by his.

Also, Dr. Conway is the author of Filter::Simple, which aids a lot blanking out PODs, strings, etc. so you can munge the source with certain confidence. Without Filter::Simple this module would be infinitely more broken.

SEE ALSO

perlfilter, Filter::Simple, SuperPython.

AUTHOR

Xavier Noria (FXN), <fxn@cpan.org>

COPYRIGHT AND LICENSE

Copyright (C) 2004 by Xavier Noria

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.2 or, at your option, any later version of Perl 5 you may have available.

cpanm Acme::Pythonic

perl -MCPAN -e shell
install Acme::Pythonic