Perl 6 中的 with orwith without

with orwith without

with 语句就像 if 但是是为了测试是否定义而非真假。此外, 它主题化了条件, 这很像 given:

with "abc".index("a") { .say } # print 0

代替 elsif, orwith 用于把是否定义的测试链接起来:

# The below code says "Found a at 0"
my $s = "abc";
with   $s.index("a") { say "Found a at $_" }
orwith $s.index("b") { say "Found b at $_" }
orwith $s.index("c") { say "Found c at $_" }
else                 { say "Didn't find a, b or c" }

你可以混合基于 if 的从句和基于 with 的从句：

# This says "Yes"
if 0 { say "No" } orwith Nil { say "No" } orwith 0 { say "Yes" };

至于 unless, 你可以使用 without 来检测未定义(undefinedness), 但是你不可以添加 else 从句:

my $answer = Any;
without $answer { warn "Got: $_" }

我们还有 with 和 without 语句修饰符：

my $answer = (Any, True).roll;
say 42 with $answer;
warn "undefined answer" without $answer;

测试下：

> my $answer = (Any, True).roll;
True
> say 42 with $answer;
42
> my $answer = (Any, True).roll;
(Any)
> say 42 with $answer;
()