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module Morpher
class Evaluator
class Transformer
# Transformer that allows to guard transformation process
# with a predicate on input
class Guard < self
include Unary, Transitive
register :guard
# Call evaluator
#
# @param [Object] input
#
# @return [Object]
# if input evaluates true under predicate
#
# @raise [TransformError]
# otherwise
#
# @api private
#
def call(input)
if operand.call(input)
input
else
fail TransformError.new(self, input)
end
end
# Return evaluation
#
# @param [Object] input
#
# @return [Evaluation::Guard]
#
# @api private
#
def evaluation(input)
operand_evaluation = operand.evaluation(input)
if operand_evaluation.output
evaluation_success(input, operand_evaluation, input)
else
evaluation_error(input, operand_evaluation)
end
end
# Return inverse evaluator
#
# @return [self]
#
# @api private
#
def inverse
self
end
end # Guard
end # Transformer
end # Evaluator
end # Morpher
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