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.
[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__ == $0 require 'test/unit'
class TestGatherer < Test::Unit::TestCase def ok(x, y) assert_equal x.to_a,y end def test_take l= gather { for i in 1..10: take i end} ok 1..10, l end def test_take2 l= gather { for i in 1..10: take i end; take 99} assert_equal (1..10).to_a+[99],l end
def test_gathered l= gather {for i in 1..10: take i end; take 99 unless gathered} ok 1..10,l end
def test_gathered_empty l= gather {take 99 unless gathered} ok 99,l end
def test_gathered_pop l= gather {for i in 1..10: take i end; gathered.pop } ok 1..9,l end end end
gabriele renzi <surrender...@remove-yahoo.it> writes: > Hi gurus and nubys,
> this morning I stumbled across the Autrijus Tang journal[1], > which was showing this nifty piece of code:
> say [~] (-> @c is copy {gather { > while @c[0] { for @c -> > {take(.shift)} } } > }(['Joec','utrk','shle','te6r',' r .','a h.','nPa.'].map:{[split "",$_]}));
> 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.
wow, I always thought GOO was cool, it seem I need to investigate it more deeply :)
> I think the implementation with instance_eval can be a bit surprising, > maybe [Dynamic Variables][1] could do that better.
yup, instance_eval is an hack, but I liked the idea of just allowing #take inside #gather, which I don't have Idea how to reproduce withouth it. Using DynaVars seem definitely a cool hack, anyway :)
gabriele renzi <surrender...@remove-yahoo.it> writes: > Christian Neukirchen ha scritto: > <snip> >> That's very nice and useful (I often wished for it), but goo already >> had it for a long time. :-) It is called "packing" there, see >> http://people.csail.mit.edu/jrb/goo/manual.46/goomanual_29.html
> wow, I always thought GOO was cool, it seem I need to investigate it > more deeply :)
If it was alive, it would be even nicer... so many good ideas but noone pushing them.
>> I think the implementation with instance_eval can be a bit surprising, >> maybe [Dynamic Variables][1] could do that better.
> yup, instance_eval is an hack, but I liked the idea of just allowing > #take inside #gather, which I don't have Idea how to reproduce > withouth it. Using DynaVars seem definitely a cool hack, anyway :)
I'd just make it raise a RuntimeError if you're not inside a gathering. Esp. in method definitions, how would you reach for "the outer self"?
"murphy" <mur...@cYcnus.de> writes: > what about a more Ruby-like extension:
> class Array > def add > yield self > self > end > end
> # simple > a = [].add do |a| > a << 1 > a << 2 > a << 3 > end > p a
> # Fibonacci > b = [1,1].add do |a| > 15.times { a << a[-1] + a[-2] } > end > p b
> Array#inject may do as well.
I think the nice thing about packings is that they don't need to reference the array variable... your code is no improvement to just appending to the array directly, IMHO.
On May 31, 2005, at 9:28 AM, Christian Neukirchen wrote:
> I think the nice thing about packings is that they don't need to > reference the array variable... your code is no improvement to just > appending to the array directly, IMHO.
In that case, how are gather/packing an improvement? They require more typing than just appending to an Array.
James Edward Gray II <ja...@grayproductions.net> writes:
> On May 31, 2005, at 9:28 AM, Christian Neukirchen wrote:
>> I think the nice thing about packings is that they don't need to >> reference the array variable... your code is no improvement to just >> appending to the array directly, IMHO.
> In that case, how are gather/packing an improvement? They require > more typing than just appending to an Array.
> I guess I just don't "get it". <shrugs>
For example, you could write methods that can add to any object responding to "<<", just whatever it is.
It's mostly convenience, I'd say. It can make the code more elegant, e.g. if you would have used #map, but sometimes need to map to several values...
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