| Name : perl-Syntax-Keyword-Gather
| |
| Version : 1.003002
| Vendor : obs://build_opensuse_org/devel:languages:perl
|
| Release : lp155.1.1
| Date : 2023-07-20 19:07:54
|
| Group : Unspecified
| Source RPM : perl-Syntax-Keyword-Gather-1.003002-lp155.1.1.src.rpm
|
| Size : 0.03 MB
| |
| Packager : https://www_suse_com/
| |
| Summary : Implements the Perl 6 \'gather/take\' control structure in Perl 5
|
Description :
Perl 6 provides a new control structure -- \'gather\' -- that allows lists to
be constructed procedurally, without the need for a temporary variable.
Within the block/closure controlled by a \'gather\' any call to \'take\' pushes
that call\'s argument list to an implicitly created array. \'take\' returns
the number of elements it took. This module implements that control
structure.
At the end of the block\'s execution, the \'gather\' returns the list of
values stored in the array (in a list context) or a reference to the array
(in a scalar context).
For example, instead of writing:
print do {
my AATTwanted;
while (my $line = < >) {
push AATTwanted, $line if $line =~ /\\D/;
push AATTwanted, -$line if some_other_condition($line);
}
push AATTwanted, \'EOF\';
join q{, }, AATTwanted;
};
instead we can write:
print join q{, }, gather {
while (my $line = < >) {
take $line if $line =~ /\\D/;
take -$line if some_other_condition($line);
}
take \'EOF\';
}
and instead of:
my $text = do {
my $string;
while (< >) {
next if /^#|^\\s*$/;
last if /^__[DATA|END]__\
$/;
$string .= $_;
}
$string;
};
we could write:
my $text = join q{}, gather {
while (< >) {
next if /^#|^\\s*$/;
last if /^__[DATA|END]__\
$/;
take $_;
}
};
There is also a third function -- \'gathered\' -- which returns a reference
to the implicit array being gathered. This is useful for handling defaults:
my AATTodds = gather {
for AATTdata {
take $_ if $_ % 2;
take to_num($_) if /[one|three|five|nine]$/;
}
take (1,3,5,7,9) unless gathered;
}
Note that -- as the example above implies -- the \'gathered\' function
returns a special Perl 5 array reference that acts like a Perl 6 array
reference in boolean, numeric, and string contexts.
It\'s also handy for creating the implicit array by some process more
complex than by simple sequential pushing. For example, if we needed to
prepend a count of non-numeric items:
my AATTodds = gather {
for AATTdata {
take $_ if $_ %2;
take to_num($_) if /[one|three|five|seven|nine]$/;
}
unshift gathered, +grep(/[a-z]/i, AATTdata);
}
Conceptually \'gather\'/\'take\' is the generalized form from which both \'map\'
and \'grep\' derive. That is, we could implement those two functions as:
sub map (&AATT) {
my $coderef = shift;
my AATTlist = AATT{shift AATT_};
return gather {
take $coderef->($_) for (AATTlist)
};
}
sub grep (&AATT) {
my $coderef = shift;
my AATTlist = AATT{shift AATT_};
return gather {
do { take $_ if $coderef->($_) } for AATTlist
};
}
A \'gather\' is also a very handy way of short-circuiting the construction of
a list. For example, suppose we wanted to generate a single sorted list of
lines from two sorted files, but only up to the first line they have in
common. We could gather the lines like this:
my AATTmerged_diff = gather {
my $a = < $fh_a>
my $b = < $fh_b>
while (1) {
if ( defined $a && defined $b ) {
if ($a eq $b) { last } # Duplicate means end of list
elsif ($a lt $b) { take $a; $a = < $fh_a> }
else { take $b; $b = < $fh_b> }
}
elsif (defined $a) { take $a; $a = < $fh_a> }
elsif (defined $b) { take $b; $b = < $fh_b> }
else { last }
}
}
If you like it really short, you can also \'gather\'/\'take\' $_ magically:
my AATTnumbers_with_two = gather { for (1..20) { take if /2/ } }; #
AATTnumbers_with_two contains 2, 12, 20
Be aware that $_ in Perl5 is a global variable rather than the current
topic like in Perl6.
|
RPM found in directory: /packages/linux-pbone/ftp5.gwdg.de/pub/opensuse/repositories/devel:/languages:/perl:/CPAN-S/15.5/noarch |
