implement strict equality operator for subclasses of Expression

lib/ruby_algebra/expression.rb

@@ -50,6 +50,12 @@ module RubyAlgebra
     def op_assoc_type
       :left
     end
+
+    def ==(other)
+      return false if other.type != type
+      lhs == other.lhs && rhs == other.rhs
+    end
+
     def diff(v)
       Addition.new(@lhs.diff(v), @rhs.diff(v))
     end
@@ -116,6 +122,11 @@ module RubyAlgebra
       :left
     end
 
+    def ==(other)
+      return false if other.type != type
+      lhs == other.lhs && rhs == other.rhs
+    end
+
     def diff(v)
       u_prime = @lhs.diff(v)
       v_prime = @rhs.diff(v)
@@ -179,6 +190,11 @@ module RubyAlgebra
       :right
     end
 
+    def ==(other)
+      return false if other.type != type
+      base == other.base && exponent == other.exponent
+    end
+
     def diff(v)
       unless @exponent.is_a?(Constant)
         raise NotImplementedError, "Дифференцирование степени с неконстантным показателем не реализовано"
@@ -215,6 +231,12 @@ module RubyAlgebra
     def op_assoc_type
       nil
     end
+
+    def ==(other)
+      return false if other.type != type
+      value == other.value
+    end
+
     def diff(v)
       Constant.new(0)
     end
@@ -248,6 +270,11 @@ module RubyAlgebra
       @is_single_letter
     end
 
+    def ==(other)
+      return false if other.type != type
+      symbol == other.symbol
+    end
+
     def diff(v)
       @symbol == v ? Constant.new(1) : Constant.new(0)
     end