On Tue, Apr 12, 2022 at 10:15 AM Luca Ferrari <[email protected]> wrote:
>
> Hello all,
> given this simple program:
>
> sub MAIN( Str :$dir where { .so && .IO.d // warn "Specify the
> directory [$dir]" } ) {
> say $dir;
> }
>
Shame on me: it works if I omit the topic and substitute it with the
explicit variable, thus:
sub MAIN( Str :$dir where { $dir.so && $dir.IO.d // warn "Specify the
directory [$dir]" } ) {
say $dir;
}
The only thing that I find in the documentation at
<https://docs.raku.org/type/Signature#index-entry-where_clause> is:
"The code in where clauses has some limitations: anything that
produces side-effects (e.g., printing output, pulling from an
iterator, or increasing a state variable) is not supported and may
produce surprising results if used. Also, the code of the where clause
may run more than once for a single typecheck in some
implementations."
Is there a better approach to spurting warning messages when a
parameter is not correct (without dealing with USAGE() and friends)?
Thanks,
Luca
