perl6:如何为函数的参数指定多个需求？

Question

我有一个特殊的函数,它接受一个列表,列表的每个成员必须满足多个要求.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;

谢谢您的帮助 !!

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where在参数中添加一个子句,以根据自定义表达式检查传入的参数.

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 ) {
    ...
}

您可以更进一步,并将整个where条款分解为subset:

subset SpecialList of List where .all ~~ SpecialNumber;

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

PS:我认为你的要求(5)可能是多余的,因为要求(6)似乎只满足奇数,但我对数论并不大,所以我不确定.