proposal: add support for ?0 to generate a random float between 0 and 1

[fzipp]

Some APL dialects (including Dyalog APL and J) feature a unary roll operator that generates a random floating-point number between 0 and 1 when the operand is zero. See https://aplwiki.com/wiki/Roll

Example:

?0
	0.945196149294

The revised doc text could be:

Roll              ?B    ?       One integer selected randomly from the first B integers
                                If B=0, random floating-point number between 0 and 1

The implementation would return

BigFloat{big.NewFloat(c.Config().Random().Float64())}

Is this something you could imagine for Ivy as well? If so, I can create a pull request.

[robpike]

That's pretty hacky but I suppose precedence makes it acceptable.

[rsc]

What about ?1.0 doing that, and similarly ?10.0 generates a random float in [0, 10.0)?

[robpike]

I like the ?float idea much better.
I wonder what we can do with ?3j2....

[robpike]

Also should bump the rand version to v2.

I'll take care of this.

[robpike]

Ah, but see golang/go#70790

So for now, just the language change. I'll file another issue for the version change.

[robpike]

Because numbers get "shrunk" as soon as they are scanned (1.0 becomes an integer in the parser, 0.5 becomes a rational, etc.), using the type to choose the roll result only works if you force it: ?float 1. That's ugly, but can work. Also, if you write ?f where f is a variable holding a float, it could cause trouble if halfway through the calculation f unexpectedly becomes an integer. This is a bug waiting to happen.

Because ?0 is also ugly (at least to me), and ?float 1 hardly better, the answer may be instead to provide a different operator for the float variant. I'll think about it.