Created
April 5, 2016 06:40
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class ZCombinator | |
def initialize improver | |
@improver = improver | |
end | |
def call gen | |
eat_its_tail(gen).( | |
->(gen) { @improver.(applicatively_eat_its_tail gen) } | |
).(gen) | |
end | |
private | |
def eat_its_tail gen | |
->(gen) { gen.(gen) } | |
end | |
def applicatively_eat_its_tail gen | |
->(_) { gen.(gen).(_) } | |
end | |
end | |
triangle = ZCombinator.new ->(partial) { ->(n) { n < 1 ? 0 : n + partial.(n.pred) } } | |
factorial = ZCombinator.new ->(partial) { ->(n) { n < 1 ? 1 : n * partial.(n.pred) } } | |
fibonacci = ZCombinator.new ->(partial) { ->(n) { n < 2 ? n : partial.(n.pred) + partial.(n.pred.pred) } } | |
Array.new(10) { |n| triangle.(n) } | |
#=> [0, 1, 3, 6, 10, 15, 21, 28, 36, 45] | |
Array.new(10) { |n| factorial.(n) } | |
#=> [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880] | |
Array.new(10) { |n| fibonacci.(n) } | |
#=> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34] |
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