Илиян обнови решението на 14.11.2012 16:31 (преди почти 13 години)
+class Expr
+ def self.build(sexpression)
+ case sexpression[0]
+ when :number then Number.new(sexpression[1])
+ when :variable then Variable.new(sexpression[1])
+ when :+ then Addition.new(build(sexpression[1]), build(sexpression[2]))
+ when :* then Multiplication.new(build(sexpression[1]), build(sexpression[2]))
+ when :- then Negation.new(build(sexpression[1]))
+ when :sin then Sine.new(build(sexpression[1]))
+ when :cos then Cosine.new(build(sexpression[1]))
+ end
+ end
+
+ def ==(other)
+ instance_of? other.class
+ end
+
+ def evaluate(environment = {})
+ end
+
+ def simplify
+ end
+
+ def derive(variable)
+ end
+
+ def exact?
+ false
+ end
+end
+
+class Unary < Expr
+ attr_accessor :operand
+
+ def initialize(operand)
+ @operand = operand
+ end
+
+ def ==(other)
+ super and operand.instance_of? other.operand.class and operand == other.operand
+ end
+
+ def exact?
+ operand.exact?
+ end
+end
+
+class Binary < Expr
+ attr_accessor :left_operand, :right_operand
+
+ def initialize(left_operand, right_operand)
+ @left_operand = left_operand
+ @right_operand = right_operand
+ end
+
+ def ==(other)
+ super and
+ left_operand.instance_of? other.left_operand.class and
+ right_operand.instance_of? other.right_operand.class and
+ left_operand == other.left_operand and
+ right_operand == other.right_operand
+ end
+
+ def exact?
+ left_operand.exact? and right_operand.exact?
+ end
+end
+
+class Number < Unary
+ def evaluate(environment = {})
+ operand
+ end
+
+ def simplify
+ Number.new(operand)
+ end
+
+ def derive(variable)
+ Number.new(0)
+ end
+
+ def exact?
+ true
+ end
+end
+
+class Addition < Binary
+ def evaluate(environment = {})
+ left_operand.evaluate(environment) + right_operand.evaluate(environment)
+ end
+
+ def simplify
+ new_left_operand, new_right_operand = left_operand.simplify, right_operand.simplify
+
+ if new_left_operand == Number.new(0)
+ new_right_operand
+ elsif new_right_operand == Number.new(0)
+ new_left_operand
+ elsif new_left_operand.exact? and new_right_operand.exact?
+ Number.new(Addition.new(new_left_operand, new_right_operand).evaluate)
+ else
+ Addition.new(new_left_operand, new_right_operand)
+ end
+ end
+
+ def derive(variable)
+ Addition.new(left_operand.derive(variable), right_operand.derive(variable)).simplify
+ end
+end
+
+class Multiplication < Binary
+ def evaluate(environment = {})
+ left_operand.evaluate(environment) * right_operand.evaluate(environment)
+ end
+
+ def simplify
+ new_left_operand, new_right_operand = left_operand.simplify, right_operand.simplify
+
+ if new_left_operand == Number.new(0) or new_right_operand == Number.new(0)
+ Number.new(0)
+ elsif new_left_operand == Number.new(1)
+ new_right_operand
+ elsif new_right_operand == Number.new(1)
+ new_left_operand
+ elsif new_left_operand.exact? and new_right_operand.exact?
+ Number.new(Multiplication.new(new_left_operand, new_right_operand).evaluate)
+ else
+ Multiplication.new(new_left_operand, new_right_operand)
+ end
+ end
+
+ def derive(variable)
+ Addition.new(
+ Multiplication.new(left_operand.derive(variable), right_operand),
+ Multiplication.new(left_operand, right_operand.derive(variable))
+ ).simplify
+ end
+end
+
+class Variable < Unary
+ def evaluate(environment = {})
+ environment[operand] or raise('Variable not found')
+ end
+
+ def simplify
+ Variable.new(operand)
+ end
+
+ def derive(variable)
+ Number.new(variable == operand ? 1 : 0)
+ end
+
+ def exact?
+ false
+ end
+end
+
+class Negation < Unary
+ def evaluate(environment = {})
+ - operand.evaluate(environment)
+ end
+
+ def simplify
+ new_operand = operand.simplify
+ new_operand.exact? ? Number.new(-new_operand.evaluate) : Negation.new(new_operand)
+ end
+
+ def derive(variable)
+ Negation.new(operand.derive(variable)).simplify
+ end
+end
+
+class Sine < Unary
+ def evaluate(environment = {})
+ Math.sin(operand.evaluate(environment))
+ end
+
+ def simplify
+ new_operand = operand.simplify
+ new_operand.exact? ? Number.new(new_operand.evaluate) : Sine.new(new_operand)
+ end
+
+ def derive(variable)
+ Multiplication.new(operand.derive(variable), Cosine.new(operand)).simplify
+ end
+end
+
+class Cosine < Unary
+ def evaluate(environment = {})
+ Math.cos(operand.evaluate(environment))
+ end
+
+ def simplify
+ new_operand = operand.simplify
+ new_operand.exact? ? Number.new(new_operand.evaluate) : Cosine.new(new_operand)
+ end
+
+ def derive(variable)
+ Multiplication.new(operand.derive(variable), Negation.new(Sine.new(operand))).simplify
+ end
+end