From: gabriele renzi <surrender_it@...>
Date: 2005-05-28T20:15:20+09:00
Subject: Useless hack of the saturday morning

Hi gurus and nubys,

this morning I stumbled across the Autrijus Tang journal[1],
which was showing this nifty piece of code:


say [~] (-> @c is copy {gather {
while @c[0] { for @c ->
{take(.shift)} } }
}(['Joec','utrk','shle','te6r',' r .','a h.','nPa.'].map:{[split "",$_]}));

in perl6 the [<something>] is the reduce metaoperator, and -> is the 
equivalent of "proc".
The hard thing was understanding what gather/take are supposed to do.
A little investigation yielded explanation[2], they seem to be some kind 
of accumulating construct a-la inject. In the tradition of the 
perl6->ruby port such as junctions, .= operator and so on I tried 
implement it.


Oh, and here is the translated JAPRH

proc{|c|p gather{c.each{|x|take x.shift}while
c[0][0]}.join}.call ['Joedh','utr a','shlRc',
'te6uk',' r be','a ayr.','nPn .' ].map{|x|x.split ''}

And down is the implementation[3]
[1] http://use.perl.org/~autrijus/journal/24919

[2] http://search.cpan.org/~dconway/Perl6-Gather-0.04/Gather.pm

[3]
class Gatherer
   attr :gathered
   def take(arg)
     @gathered||=[]
     @gathered<< arg
   end
end

def gather &blk
   c=Gatherer.new
   c.instance_eval &blk
   c.gathered
end

if __FILE__ == $0
   require 'test/unit'

   class TestGatherer < Test::Unit::TestCase
     def ok(x, y)
       assert_equal x.to_a,y
     end
     def test_take
       l= gather { for i in 1..10: take i end}
       ok 1..10, l
     end
     def test_take2
       l= gather { for i in 1..10: take i end; take 99}
       assert_equal (1..10).to_a+[99],l
     end

     def test_gathered
       l= gather {for i in 1..10: take i end; take 99 unless gathered}
       ok 1..10,l
     end

     def test_gathered_empty
       l= gather {take 99 unless gathered}
       ok 99,l
     end

     def test_gathered_pop
       l= gather {for i in 1..10: take i end; gathered.pop  }
       ok 1..9,l
     end
   end
end