pvar_expr : IDENT LPAREN term_list RPAREN
                     | IDENT

def p_pvar_expr(self, p):
        '''pvar_expr : IDENT LPAREN term_list RPAREN
                     | IDENT'''
        if len(p) == 2:
            p[0] = ('pvar_expr', (p[1], None))
        elif len(p) == 5:
            p[0] = ('pvar_expr', (p[1], p[3]))