Support additional number bases

[Stupremee]

It would be very helpful if you can specify numbers in other bases, e.g. hexadecimal (0xFF) or binary (0b1001), and convert them via functions like in Python. (hex(255) -> 0xFF, bin(2) -> 10)

[likebike]

Great idea. I'll try to add this soon.

[Stupremee]

I can add this if it's okay.

[likebike]

I can add this if it's okay.

Sure, you can if you want to. You mostly just need to modify the read_const() function: https://github.com/likebike/fasteval/blob/master/src/parser.rs#L345

[Stupremee]

Yep already saw it

[likebike]

As far as the idea about hex()/bin()/... functions goes, that's going to be a bit complicated. Those functions would need to produce strings, not numbers, and they could only be used as arguments within a print() function (because that is the only place where strings are allowed).

...So i suggest that we first just implement the parsing of numeric literals ( 0xFF, 0b010101, 0o746 ), and ignore the string formatting for now.

[likebike]

Instead of using functions like hex()/bin()/oct()/..., another way to do the string formatting of alternate bases is by using printf-style formatting codes, like this: print("hex=%x dec=%d oct=%o bin=%b", 100, 100, 100, 100)

I like Go's choice of formatting codes: https://golang.org/pkg/fmt/#hdr-Printing

I am already planning to add printf codes to print(). In fact, my Go implementation of this library already has that feature, but dynamic string formatting is not a built-in feature in Rust, so I will need to implement it myself.

[Stupremee]

That’s a good idea 👍.
Rust formatting has support for hex, oct and binary. Probably you can use that.

[likebike]

The Rust formatting is really nice, but it is compile-time only. fasteval needs runtime formatting. Maybe we can find a way to re-use the Rust formatting infrastructure at runtime.

[Stupremee]

Can't you just use the format macro?

[likebike]

All macros are evaluated at compile-time. We need a solution that can perform string formatting at run-time.

[Stupremee]

Ohh, yes you are right.

[Stupremee]

I don't have much time at the moment. So the PR will take around a week.

[likebike]

No problem. Take your time -- I appreciate your help.