Trey Harris wrote:
> markstos++ pointed out the following behavior:
>
> use v6-alpha;
>
> {
> when 1 ~~ 0 {
> say "Surprise!"
> }
> }
>
> This code prints "Surprise!", because $_ is undef, which is false, just
> like 1 ~~ 0 is.
>
> I'd like to make the following suggestions for Synopsis clarification:
>
> 1. It will be a very common pitfall, I think, to write C<when> as a
> synonym for C<if>. For an extra layer of safety for such a novitiate
> mistake, a boolean used as an argument to when should emit a warning
> unless suppressed with an explicit C<?()>.
>
> when 1 ~~ 0 # warning
> when ?(1 ~~ 0) # no warning
>
> 2. I think C<when> should either be disallowed outside of C<given>, or
> it should be made to do something useful.
To refine this point a bit, the spec is clear that 'when' is useful not
just with 'given' but with "any block that sets $_".
I agree that it should be an error outside of "any block that sets $_",
and I ask that that "any block that sets $_" be further defined. "for"
statements and method bodies are mentioned explicitly, but it would be
nice to have something approach a complete list.
Mark
