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@andkerosine
Created August 15, 2012 05:56
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Haskell-like list comprehensions in Ruby
$stack, $draws = [], {}
def method_missing *args
return if args[0][/^to_/]
$stack << args.map { |a| a or $stack.pop }
$draws[$stack.pop(2)[0][0]] = args[1] if args[0] == :<
end
class Array
def +@
$stack.flatten!
keys = $draws.keys & $stack
draws = $draws.values_at *keys
comp = draws.shift.product(*draws).map do |draw|
$stack.map { |s| draw[keys.index s] rescue s }.reduce do |val, cur|
op = Symbol === cur ? [:send, :method][val.method(cur).arity] : :call
val.send op, cur
end
end
$stack, $draws = [], {}
Symbol === last ? comp.select(&pop) : comp
end
def -@
case map(&:class).index Range
when 0 then first.to_a
when 1 then [first] + last.step(last.min.ord - first.ord).to_a
else self
end
end
end
foo =+ [x * y | x <- [1..3], y <- [4..6]]
# [4, 5, 6, 8, 10, 12, 12, 15, 18]
bar =+ [a + b | a <- ['n','p'..'t'], b <- %w[a i u e o]]
# ["na", "ni", "nu", "ne", "no", "pa", "pi", "pu", "pe", "po", "ra", "ri", "ru", "re", "ro", "ta", "ti", "tu", "te", "to"]
baz =+ [i ** 2 / 3 | i <- [3,6..100], :even?]
# [12, 48, 108, 192, 300, 432, 588, 768, 972, 1200, 1452, 1728, 2028, 2352, 2700, 3072]
quux =+ [s.size.divmod(2) | s <- %w[Please do not actually use this.]]
# [[3, 0], [1, 0], [1, 1], [4, 0], [1, 1], [2, 1]]
@linduxed
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Looks really nice!

@freakhill
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I played a bit with the idea to get that. Trying out ruby2 refinements. Too lazy for the "|" support but can do conditions.
https://gist.github.com/freakhill/5564328

@igbanam
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igbanam commented May 12, 2013

+1 for "Raskell". Pun in "Rascal"?

@darth10
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darth10 commented May 13, 2013

Awesome job! ❤️ Gem it please?

@wteuber
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wteuber commented May 15, 2013

"Haskell-like" without lambdas?
Even if it doesn't look as much like Haskell, this snippet is much closer to the Haskell principles, without abusing Ruby.

foo = ->(x=(1..3), y=(4..6)){x.flat_map{|a| y.map{|b| a*b}}}.call

(Of course you usually wouldn't need to call any lambdas before actually executing the application)

@hauleth
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hauleth commented May 18, 2013

Nice but for Ruby I prefer using Ruby syntax:

(1..3).zip(4..6).map { |a, b| a * b }

@chrislerum
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I'd humbly like to up-vote the previous comment.

@whistler
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Thats quite brilliant, the author does say "Please do not actually use this."
@hauleth zip is a bit different, list comprehensions are more like cross products:

(1..3).to_a.product((4..6).to_a).map{|a,b| a*b}

or you could do a double map_flat like @wteuber.

@josiah14
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Impressive.

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