parameters - perl6 : how to specify multiple requirements for a parameter of a function?

Question

我有一个接受列表的特殊函数，列表中的每个成员都必须满足多个要求。我如何在 perl6 函数中设置它？

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，但您可以添加 where子句到您的参数以根据自定义表达式检查传入参数。

为清楚起见，我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 ) {
    ...
}

你可以更进一步，把整个 where 分解出来。条款变成 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)似乎只能满足奇数，但我对数论并不了解，所以我不确定。