Comment by sevensor
5 hours ago
But given the definition of Fibable, it could be anything that supports + and - operators. That could be broader than numbers. You could define it for sets for example. How do you add the number 1 to the set of strings containing (“dog”, “cat”, and “bear”)? So I suppose I do have a complaint about Fibable, which is that it’s underconstrained.
Granted, I don’t know nim. Maybe you can’t define + and - operators for non numbers?
Araq was probably trying to keep `Fibable` short for the point he was trying to make. So, your qualm might more be with his example than anything else.
You could add a `SomeNumber` predicate to the `concept` to address that concern. `SomeNumber` is a built-in typeclass (well, in `system.nim` anyway, but there are ways to use the Nim compiler without that or do a `from system import nil` or etc.).
Unmentioned in the article is a very rare compiler/PLang superpower (available at least in Nim 1, Nim 2) - `compiles`. So, the below will print out two lines - "2\n1\n":
Last I knew "concept refinement" for new-style concepts was still a work in progress. Anyway, I'm not sure what is the most elegant way to incorporate this extra constraint, but I think it's a mistake to think it is unincorporatable.
To address your question about '+', you can define it for non-SomeNumber, but you can also define many new operators like `.+.` or `>>>` or whatever. So, it's up to your choice/judgement if the situation calls for `+` vs something else.
That’s fair. Sounds like the example was composed in haste and may not do the language justice.
I think the example was chosen only for familiarity and is otherwise not great. Though it was the familiarity itself that probably helped you to so easily criticize it. So, what do I know? :-)
FWIW, the "catenation operator" in the Nim stdlib is ampersand `&`, not `+` which actually makes it better than most PLangs at visually disambiguating things like string (or other dynamic array, `seq[T]` in Nim) concatenation from arithmetic. So, `a&b` means `b` concatenated onto the end of `a` while `a+b` is the more usual commutative operation (i.e. same as `b+a`). Commutativity is not enforced by the basic dispatch on `+`, though such might be add-able as a compiler plugin.
Mostly, it's just a very flexible compiler / system.. like a static Lisp with a standard surface syntax closer to Python with a lot of parentheses made optional (but I think much more flexible and fluid than Python). Nim is far from perfect, but it makes programming feel like so much less boilerplate ceremony than most alternatives and also responds very well to speed/memory optimization effort.