Fair point. I should mention that I'm not a Nim expert, and am not defending its design. It's true that 'nil' appears in Nim under both of its pointer types (GC traced "references" and untraced "pointers") -- which is unlike, say, Rust's safe references vs. unsafe (nullable) pointers. So 'nil' is not simply a systems level construct; otherwise you might expect Nim to have nillable pointers, but not nillable references.
You need nil/null when doing systems work -- and Nim is capable of that -- but I don't know the rationale for allowing 'nil' in higher level language features.
"We need the nil state to disarm pointers but that only means these can be nil and so would require a nil check before deref. Doesn't seem to be too hard nor too cumbersome."
`non-nil` was deemed too breaking to introduce for 1.0 or even as a default because if you tagged your input as `T not nil` the compiler was not powerful enough to prove that T was indeed not nil except in the most obvious cases.
The new battleplan is to integrate the Z3 theorem prover into Nim as DrNim:
I agree that it's a sharp edge in the language. Or at least it seems to be -- I've written a little bit of Nim, and never encountered a case where I was actually bitten by 'nil'. The language does have a 'non nil' annotation that can be used when defining structs (and maybe in other parts of the language, I don't recall), so there must have been some thinking about the dangers of nil pointers.
I would still recommend playing with the language for a while. It's quite practical, and the performance is very good. I've used it to write some utilities where I might otherwise use Python, but either needed more speed or needed to use it in a restricted environment where the Python interpreter wasn't available. The experience was mostly positive, and I would use it again.
That's an old comment by the way. At that time the newruntime idea was tested (and now replaced by --gc:arc). One needs to be more careful when using others words, especially taken out of context.