Even if it would accept the when, it may still not do what you expect it to. In 
given ($var) {
    ... use of $_ ...
}

[download]
$_ is a copy of $var. Any modifications to $_ will not propagate to $var. But you could write: 
for ($var) {
    ... when clauses ...
    if (s{^cpan://}{http://search.cpan.org/search?query=}p) {
       ...
       last;
    }
    ... more when clauses ...
}

[download]

In reply to Re: "when" and replacements by JavaFan
in thread "when" and replacements by John M. Dlugosz

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