> On Dec 19, 2020, at 6:40 PM, ToddAndMargo via perl6-users
> <perl6-us...@perl.org> wrote:
>
> Hi All,
>
> I have so far:
>
>
> class BadMath {
> has Int $.A;
> has Int $.B;
>
> method BadAdd() {
> my $Clinker = (-5..5).rand.truncate;
> return $!A + $!B + $Clinker;
> }
> }
>
>
> my $TwoPlusTwo = BadMath.new( A => 2, B=> 2 );
> print $TwoPlusTwo.BadAdd ~ "\n";
>
>
> How do I modify the declaration such that I can
> address the method as such?
>
> say (2,2).BadAdd;
> No such method 'BadAdd' for invocant of type 'List'
>
>
> I want my 10 in 11 chance to win a participation trophy!
>
> Many thanks,
> -T
You cannot do that.
(Except that you *technically* can, but shouldn't; see
https://docs.raku.org/syntax/augment , which shows how to do it, and also says
..."strongly discouraged. For almost all situations, there are better
solutions.")
You can combine the object creation and the method call in one statment:
say BadMath.new( A => 2, B=> 2 ).BadAdd;
With a custom `new` method, that could be shortened further to:
say BadMath.new(2, 2).BadAdd;
But your desired syntax (`(2,2).BadAdd`) seems to hinge on never moving (2,2)
into a BadMath object.
To make that work, you would have to add the `BadAdd` method to Raku's built-in
List type via `MONKEY-TYPING` and `augment`.
Very highly non-recommended.
We do have `.&` syntax for when you want to call a sub like a method:
sub BadAdd ( ($a, $b) ) { # Notice the extra parentheses
$a + $b + (-5..5).rand.truncate;
}
# say (2,2).BadAdd; # Will fail
say (2,2).&BadAdd; # Works!
You get to use BadAdd *almost* like a method, and you do not need to define a
Class or any other OO stuff.
We also offer easy do-it-yourself custom operators:
multi sub infix:<+bad+> ($a, $b) {
return $a + $b + (-5..5).rand.truncate;
}
say 2 +bad+ 2; # Said '6' when I ran it.
The `.&` syntax or user-defined operator are the best I can offer at the moment.
This may be a XY problem. If not, more info on your intended use case may
inspire other ideas..
https://xyproblem.info/
By the way, `(-5..5).rand.truncate` does not do what it appears to do, so
either it is calculating incorrectly, or it will be confusing to any future
maintenance programmer.
$ raku -e 'my %h = bag map {(-5..5).rand.truncate}, ^100_000; .say for
%h.sort(+*.key);'
-4 => 9892
-3 => 9972
-2 => 9889
-1 => 10072
0 => 20126 # !!! Twice the average of the rest!
1 => 10029
2 => 9943
3 => 10053
4 => 10024
A reader would see that -5 and 5 are the endpoints, but the effect of
`rand.truncate` is to produce integers ±4 , not ±5.
Also, 0 has twice the chance of occurring as any other number.
For the behaviour that I suspect you want (a unweighted random integer between
-5 and 5), use:
(-5..5).pick
If the current behavior is really what you want, then the code would be less
mystifying as:
(0, |(-4..4)).pick
For more detail on Raku Randomess, you might enjoy the first third of my 2018
talk:
https://www.youtube.com/watch?v=DJCp6k1ts3g
Perl 6 and the Emergent Program.*
3m22s - 13m33s
--
Hope this helps,
Bruce Gray (Util of PerlMonks)
