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joyrexus/y.coffee

Created September 21, 2013 04:38
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Y-combinator
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y.coffee
# http://en.wikipedia.org/wiki/Fixed-point_combinator#Y_combinator
#
# λf . (λx . x x)(λy . f (λv . ((y y) v)))
Y = (f) -> ((x) -> x x)((y) -> f ((v) -> (y y) v))
# or ...
Y = (f) ->
p = (h) ->
(x) -> f(h(h))(x)
p p
fib = (f) ->
(n) -> if n == 0 then 1 else n * f(n - 1)
console.log Y(fib) i for i in [0 .. 6] # 1 1 2 6 24 120 720
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