Just another example of a conversion (using the boilerplate recipe). I'm posting mostly so it will be here to refer back to if I revisit the topic. It's interestingly different from the other examples, and the recipe still works well (although I get a curious
Use of uninitialized value in array element warning if I don't turn those warnings off (which I do, below)).
What I'm generating is permutations, like Algorithm::Loops NextPermute.
#!perl
use strict;
use warnings;
sub no_repeat_combos {
return [@_] unless @_ > 1;
# Find the first occurrence of each unique element
my %seen;
defined($seen{$_[$_]}) or $seen{$_[$_]} = $_ for 0..$#_;
# For each unique element, stick it on the front of each
# of the no-repeat-combos of the rest
map {
my $first_pos = $_;
my @rest = @_[ grep {$first_pos != $_} 0..$#_ ];
map [$_[$first_pos], @$_], no_repeat_combos(@rest);
} (sort {$a <=> $b} values %seen);
}
sub nrc_iter {
# Base cases get assigned to an array, which the iterator shifts t
+hrough
my @base_case = ([@_]);
return sub{ shift @base_case } unless @_ > 1;
# Find the first occurrence of each unique element
my %seen;
defined($seen{$_[$_]}) or $seen{$_[$_]} = $_ for 0..$#_;
# For each unique element, stick it on the front of each
# of the no-repeat-combos of the rest
my @arg_list = @_;
my @sub_iter =
map {
my $first_pos = $_;
my @rest = @_[ grep {$first_pos != $_} 0..$#_ ];
sub {
my $recurse = nrc_iter(@rest);
my $set;
no warnings 'uninitialized';
sub { ($set = $recurse->()) ? [$arg_list[$first_pos], @$set]
+ : () }
}
} sort {$a <=> $b} values %seen;
# Below here is boilerplate: if you've done the above steps right,
+ just plug
# this in, and it works. It returns the first iterator from the li
+st that
# returns anything.
# Grab and unwrap an iterator from the list
my $iter = (shift @sub_iter)->();
return sub {
my $rval;
$iter = (shift @sub_iter)->()
until ($rval = $iter->() or @sub_iter == 0);
return $rval;
}
}
for ([1], [1,1], [1,2], [qw(a b a)], [qw(a b b a)]) {
print "=== @$_ ===\n";
my $i = nrc_iter(@$_);
print " @$_\n" while $_ = $i->();
}
Caution: Contents may have been coded under pressure.
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