> On 16 Sep 2017, at 13:32, Norman Gaywood <ngayw...@une.edu.au> wrote:
>
> I have this:
> #!/usr/bin/perl6
> use v6;
> sub MAIN( :$debug = False, :$verbose = False ) {
> $verbose = True if $debug;
> say "verbose={$verbose}, debug={$debug}";
> }
> $ ./tt.p6
> verbose=False, debug=False
> $ ./tt.p6 --verbose
> verbose=True, debug=False
> $ ./tt.p6 --debug
> Cannot assign to a readonly variable ($verbose) or a value
> in sub MAIN at ./tt.p6 line 6
> in block <unit> at ./tt.p6 line 4
>
> So $verbose is read-only. I think the compiler could have told me this a
> compile time?
>
> I try to fix it:
> ...
> sub MAIN( :$debug = False, :$verbose is rw = False ) {
> ...
> $ ./tt.p6 --debug
> ===SORRY!=== Error while compiling /home/ngaywood/./tt.p6
> Cannot use 'is rw' on optional parameter '$verbose'.
> at /home/ngaywood/./tt.p6:4
>
> Not sure what the neat way of doing this is.
You probably want “is copy” here? I mean, you want to be able to change it
*within* MAIN, no?
sub MAIN( :$debug = False, :$verbose is copy = False ) {
$verbose = True if $debug;
say "verbose={$verbose}, debug={$debug}";
}
then works fine with —debug .
Liz
