perl6：如何为函数的参数指定多个要求？

Question

我有一个特殊的函数，它需要一个列表，列表的每个成员都必须满足多个要求。如何在 perl6 函数中进行设置？

sub specialFunc(List $x) {};

(1) $x is a list # easy, List $x, but what about the following:
(2) each member of $x is numeric
(3) each member of $x is positive
(4) each member of $x is greater than 7
(5) each member of $x is odd number
(6) each member of $x is either the square or the cube of an even number plus 1;

感谢您的帮助！！

lisprog

Answer 1

Perl 6 类型系统不够灵活，无法以声明方式表达此类约束，但您可以在参数中添加 where 子句，以根据自定义表达式检查传入参数。

为了清楚起见，我会将用于测试每个数字的表达式分解为subset：

subset SpecialNumber of Numeric where {
       $_ > 7                        # (3), (4)
    && $_ !%% 2                      # (5), since "odd" implies "not even"
    && .narrow ~~ Int                # (5), since "odd" implies "integer"
    && ($_ - 1) ** (1/2 | 1/3) %% 2  # (6)
}

sub specialFunc(List $x where .all ~~ SpecialNumber ) {
    ...
}

您可以更进一步，将整个where 子句分解为subset：

subset SpecialList of List where .all ~~ SpecialNumber;

sub specialFunc(SpecialList $x) {
    ...
}

PS：我认为您的要求（5）可能是多余的，因为要求（6）似乎无论如何只能满足奇数，但我对数论并不了解所以我不确定。