Script with a variable number of Real arguments

Question

I'm trying to write a Raku script to be called e.g.

script 1.2 1.117 -2 0.037

I.e., the idea is to create a sub MAIN(@numbers) and somehow get the array @numbers as Real (not Str, not IntStr). A way to do so is to cast each element (if possible) in a for, but I'm sure there is a more elegant solution.

Answer 1

I'll let readers judge whether the following is a technically atrocious hack, or looks hideously repugnant, or both. But it's the closest thing I'm aware of in current Raku syntax.

First, you need to accept a variable number of arguments. (You need that for even your code to work at all. I presume you typo'd.)

Rather than use * or similar I'll use |. We'll see why in a mo.

sub MAIN( |numbers ) { ... }

Next, I add a sub-signature.

sub MAIN( |numbers ( *@, :@reals = numbers».Real )) { ... }

This takes advantage of:

• Named parameters being optional; and

• Establishing a default value based on arguments bound to parameters to the left in a signature; and

• Hiding this chicanery so the usage message is not affected, and so that (I think) the user cannot inject a value using --reals=... or similar. (Actually, saying I think they can't is far too strong. I hope they can't.)

This is either a pretty terrible hack or just plain evil. Don't do this at home work!

The code so far presumes that the arguments are indeed Reals. If they're not, things go wrong. We need to deal with that too.

So we add a subset and add that to the signature:

subset Reals where *».Real».defined.all;
sub MAIN( Reals |numbers ( *@, :@reals = numbers».Real )) { ... }

Here we see the main reason I used | rather than *; it's the only way to write a type on the left of a slurpy, Without that I'd have to inline the where and the whole thing would be even more unspeakably ugly than it is.

Thus we end up with:

subset Reals where *».Real».defined.all;
sub MAIN( Reals |numbers ( *@, :@reals = numbers».Real )) { .WHAT.say for @reals }

displaying, for your original command line:

(Rat)
(Rat)
(Int)
(Rat)