case_def : CASE term COLON expr
                    | DEFAULT COLON expr

def p_case_def(self, p):
        '''case_def : CASE term COLON expr
                    | DEFAULT COLON expr'''
        if len(p) == 5:
            p[0] = ('case', (p[2], p[4]))
        elif len(p) == 4:
            p[0] = ('default', p[3])