Agrego paréntesis y menos

examples/calculator_with_precedence/lexer.py

@@ -24,11 +24,16 @@ tokens = (
     'PLUS',
     'TIMES',
     'MINUS',
+    'LEFT_PAR',
+    'RIGHT_PAR',
 )
 
 t_PLUS = r'\+'
 t_MINUS = r'-'
 t_TIMES = r'\*'
+t_LEFT_PAR = r'\('
+t_RIGHT_PAR = r'\)'
+
 """Esta variable especial ignora estos caracteres"""
 t_ignore = " \t"
 

examples/calculator_with_precedence/parser.py

@@ -5,8 +5,10 @@ from lexer import tokens
 precedence = (
     ('left', 'PLUS', 'MINUS'),
     ('left', 'TIMES'),
+    ('right', 'UMINUS')
 )
 
+
 def p_expression_plus(p):
     'expression : expression PLUS expression'
     p[0] = p[1] + p[3]
@@ -24,11 +26,20 @@ def p_expression_term(p):
     'expression : NUMBER'
     p[0] = p[1]
 
+def p_expression_parenthesis(p):
+    'expression : LEFT_PAR expression RIGHT_PAR'
+    p[0] = p[2]
+
+def p_minus_expression(p):
+    'expression : MINUS expression %prec UMINUS'
+    p[0] = -p[2]
+
 def p_error(p):
     print("Hubo un error en el parseo.")
 
     parser.restart()
 
+
 # Build the parser
 parser = yacc.yacc(debug=True)
 

examples/calculator_with_precedence/test.py

@@ -20,5 +20,12 @@ class ParserTest(unittest.TestCase):
 
     def test_suma_y_multiplica(self):
         self.assertEqual(parse("2 + 4 * 3"), 14)
+
+    def test_resuelve_parentesis(self):
+        self.assertEqual(parse("(2 + 3) * 4"), 20)
+
+    def test_resuelve_negacion(self):
+        self.assertEqual(parse("-2"), -2)
+
 if __name__ == '__main__':
     unittest.main()