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
解决方法
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.
为清楚起见,我将用于测试每个数字的表达式分解为一个子集：
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子句分解为子集：
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.