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
