From: Lui Core <usurffx@...>
Date: 2009-06-10T11:07:28+09:00
Subject: Writing a Y-Combinator in Ruby 1.9

i've read
http://weblog.raganwald.com/2007/02/guest-blogger-tom-moertel-derives-y.html
and finally figured out this:

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# a trick to make currying easier
class Proc
  def -@
    self.curry
  end
end

def Y &f
  g = --> h, x, *xs { f[h[h], x, *xs] }
  g[g]
end
------------------------------------------------------


and had a try:

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factorial = Y {|f, n| n == 0 ? 1 : f[n - 1] * n}
puts factorial[12]
# => 479001600

fibbonaci = Y {|f, n| n <= 2 ? 1 : f[n - 1] + f[n - 2]}
puts fibbonaci[10]
# => 55
------------------------------------------------------


the intresting part is:
if you replace "x, *xs"(like pattern matching in functional languages
^_^) with "*args", it overflows the stack.
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