58 lines
1.2 KiB
Ruby
58 lines
1.2 KiB
Ruby
# frozen_string_literal: true
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module MutualRecursion
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class TailCall
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attr_reader :value, :block
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def initialize(value = nil, &block)
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@value = value
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@block = block
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end
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##
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# Invoke this tail call. Only the returned value from the initial call to
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# the recursive function should be invoked.
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#
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# @return [Object] the terminal_value of this tail call
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def invoke
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self.then do |tail|
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while tail.block
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tail = tail.block.call
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raise MissingTailCallError unless tail.is_a?(TailCall)
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end
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tail.value
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end
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end
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end
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class MissingTailCallError < StandardError
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def initialize(msg = 'expected a tail call')
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super
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end
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end
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module_function
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##
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# Make a direct or indirect recursive call in tail position.
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#
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# @yieldreturn [MutualRecursion::TailCall] a tail call
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# @return [MutualRecursion::TailCall] a non terminal tail call
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def tail_call
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TailCall.new { yield }
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end
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##
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# Indicates that the recursion has ended with the provided value.
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#
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# @param [Object] value the terminal value
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# @return [MutualRecursion::TailCall] a terminal tail call that will return the given value
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def terminal_value(value)
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TailCall.new(value)
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end
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end
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