Thanks again.
I'm trying to get proficiency in Raku by converting some Python programs
mine in Raku.
On Mon, Jun 22, 2020 at 6:41 PM Tobias Boege <t...@taboege.de> wrote:
> On Mon, 22 Jun 2020, Aureliano Guedes wrote:
> > Thank you for the clarification.
> >
> > There is a method to set Rat precision at the scope of the program to
> apply
> > to all *.Rat() cases?
> >
>
> I don't know, based on a quick search in the documentation, of any global
> setting. The hacky solution would be to wrap the method like this:
>
> say pi.Rat.nude; # OUTPUT: (355 113)
>
> Num.^find_method('Rat').wrap: -> |c {
> # Make the default argument 1e-20
> callwith |(|c, 1e-20 if c.elems ≤ 1)
> };
>
> say pi.Rat.nude; # OUTPUT: (245850922 78256779)
>
> This program has three parts. First, we print pi.Rat.nude for comparison.
> The nude method returns numerator and denominator of a Rat as a list.
> The last part is just looking at pi.Rat.nude again to confirm that the
> change in the middle has worked and increased the default precision.
>
> You said you are relatively new to Raku, so let me explain the middle part.
> Raku has a special syntax for calling metamethods (i.e. doing
> introspection)
> on an object or type, which is the .^ operator. I use it to access an
> object
> representation of the Rat method on the Num type. I can wrap some code of
> my liking around this method via its wrap method.
>
> The `-> |c { … }` syntax creates an anonymous code block that wraps around
> the Num.Rat method and it accepts all arguments that may be passed as a
> Capture [1] in the variable c. If that Capture does not have a first
> parameter, i.e. the precision is not specified, I sneak in my 1e-20.
> Afterwards, the `callwith |(…)` part unpacks the (modified) captured
> arguments and calls the original method that I am wrapping [2].
>
> Effectively, I pass a precision of 1e-20 whenever the caller did not pass
> a precision. You can see that the wrapping takes effect immediately in
> the last line of the above program.
>
> Ideally, this could be turned into a module that hides the questionable
> means behind a dynamic $*RAT-PRECISION variable or so. That is, unless
> someone comes up with an even better solution.
>
> Best,
> Tobias
>
> [1] https://docs.raku.org/type/Capture
> [2] https://docs.raku.org/routine/wrap
>
> --
> "There's an old saying: Don't change anything... ever!" -- Mr. Monk
>
--
Aureliano Guedes
skype: aureliano.guedes
contato: (11) 94292-6110
whatsapp +5511942926110
