perlmeditation
iblech
<p>Having ported [http://svn.perl.org/perl6/pugs/trunk/modules/|20 Perl 5 CPAN modules] to [http://dev.perl.org/perl6|Perl 6] in the last few days, these are some things I noticed:</p>
<readmore>
<ul>
<li>Perl 6 is sexy! :)</li>
<li>Before you start porting a module, make sure you understand the class hierarchy of that module. It helps if you've actually used that module in Perl 5 :)</li>
<li>Port a module even if it depends on some other (not yet ported) modules -- the dependencies can be ported later on.</li>
<li>Often, the translation P5 → P6 is quite mechanic:
<ul>
<li><code>$array[idx]</code> →<br /> <code>@array[idx]</code></li>
<li><code>a ? b : c</code> →<br /> <code>a ?? b :: c</code></li>
<li><code>$self->method(...)</code> →<br /> <code>.method(...)</code></li>
<li><code>sub { my ($self, $a, $b) = @_; ... }</code> →<br /> <code>method($a, $b) { ... }</code></li>
<li><code>$x =~ s/.../.../g</code> →<br /> <code>$x ~~ s:g/.../.../</code></li>
<li><code>$self->{foo}</code> →<br /> <code>$.foo</code></li>
<li><code>$foo = "bar" unless defined $foo</code> →<br /> <code>$foo //= "bar" # (//) and (//=) will be in 5.9, too, IIRC</code></li>
<li><code>if($foo eq "a" or $foo eq "b" or $foo eq "c") {...}</code> →<br /> <code>if $foo eq "a"|"b"|"c" {...}</code></li>
<li><code>foreach my $foo (@baz) {...}</code> →<br /> <code>for @baz -> $foo {...}</code></li>
<li>Regular expressions:
<ul><li><code>[abc]</code> → <code><[abc]></code></li>
<li><code>[^abc]</code> → <code><-[abc]></code></li>
<li><code>(?:...)</code> → <code>[...]</code></li></ul></li></ul></li>
<li>Often, you can remove all that Perl 5 argument parsing and simply substitute it by a nice subroutine|method|whatever signature.</li>
<li>
<code>
# This Perl 5 exporting code...
require Exporter;
our @ISA = qw< Exporter >;
our @EXPORT = qw< foo >;
sub foo {...}
# ...becomes this in Perl 6:
sub foo(...) is export {...}
</code></li>
<li><code>return map {.4.} sort {.3.} grep {.2.} map {.1.}</code> →<br />
<code>map {.1.} ==> grep {.2.} ==> sort {.3.} ==> map {.4.} ==> return</code></li>
<li>Especially Perl 6's translation of Perl 5's getter/setter idiom is cool:<br />
<code>
# Perl 5
sub get_foo {
my $self = shift;
my $ret = $self->{foo};
return lc $ret; # always normalize
}
sub set_foo {
my ($self, $to) = @_;
$to =~ s/\s+$//; # strip whitespace at the end
$self->{foo} = $to;
}
# Perl 6:
has $:foo;
sub foo() is rw {
return new Proxy:
FETCH => { lc $:foo },
STORE => -> $to is copy {
$to ~~ s/\s+$//;
$:foo = $to;
};
}
# And then:
say $obj.foo;
$obj.foo = "...";
# Notice: Standard assignment syntax!
# Assignments should look line assingments, not like method calls
</code></li>
<li>If you trust the user to give correct data to accessors, you can also use:<br />
<code>
has $.foo is rw;
</code>
Alternatively, if you don't trust The Evil Users:<br />
<code>
subtype OddInt of Int where { $^n % 2 == 1 }
has OddInt $.foo is rw;
# And then:
$obj.foo = 12; # will die (at compile-time!)
</code>
</li>
</ul>
</readmore>
<p>You can find a perhaps more recent version of this document in the [http://svn.perl.org/perl6/pugs/trunk/modules/PORTING_HOWTO|Pugs SVN repository].</p>
<p>--Ingo</p>