if_statement : IF LPAREN cond RPAREN true_statement ELSE else_statement

def p_if_statement(self, p):
        'if_statement : IF LPAREN cond RPAREN true_statement ELSE else_statement'
        p[0] = IfStatement(p[3], p[5], p[7], lineno=p.lineno(1))
        p.set_lineno(0, p.lineno(1))