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To represent a null pointer. Nim is a systems language (or at least can be used as one), and you need null/nil when working at that level. Even Haskell has nul

To represent a null pointer. Nim is a systems language (or at least can be used as one), and you need null/nil when working at that level. Even Haskell has null pointers, if you know where to look: https://hackage.haskell.org/package/base-4.14.0.0/docs/Foreign-Ptr.html#v:nullPtr https://hackage.haskell.org/package/base-4.14.0.0/docs/Forei...

Isomorpheus 6y ago
Likewise unsafe Rust has null pointers, but I've never needed it or seen it used. (Same with Haskell). You just mentioned using "nil" in a simple example which doesn't appear to be related to systems programming.
- gmfawcett 6y ago
  I didn't mention "nil" in a simple example. I wasn't the poster of that comment.
  - Isomorpheus 6y ago
    Oh, thought you were same poster. Well, that other person mentioned it in a context which doesn't appear to be related to systems programming. Just checked Github for some of the top Nim projects. Forum software: https://github.com/nim-lang/nimforum/search?q=nil&unscoped_q=nil https://github.com/nim-lang/nimforum/search?q=nil&unscoped_q... Web framework: https://github.com/planety/prologue/search?q=nil&unscoped_q=nil https://github.com/planety/prologue/search?q=nil&unscoped_q=... Twitter front-end: https://github.com/zedeus/nitter/search?q=nil&type=Code https://github.com/zedeus/nitter/search?q=nil&type=Code These uses of "nil" don't appear to have anything to do with systems programming.
    - gmfawcett 6y ago
      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.
      - Isomorpheus 6y ago
        Thanks for the honest reply. Nim interests me but this nil business seems questionable to me. Just found this comment from the language creator, https://github.com/nim-lang/Nim/issues/6638#issuecomment-487633727 https://github.com/nim-lang/Nim/issues/6638#issuecomment-487... "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." Seems a bit dismissive to me
        gmfawcett 6y ago
        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.
        Isomorpheus 6y ago
        Thanks, I intend to give it a fair try
        elcritch 6y ago
        P.S., you can annotate procedure to help ensure you can’t raise certain conditions in code. Imho it’s nice for writing sections of “safe” code.
        mratsim 6y ago
        `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: - https://nim-lang.org/docs/drnim.html https://nim-lang.org/docs/drnim.html The first use-case will be proving array bounds at compile-time and elide them. Future use-cases include not nil tracking.

Isomorpheus 6y ago

Likewise unsafe Rust has null pointers, but I've never needed it or seen it used. (Same with Haskell). You just mentioned using "nil" in a simple example which doesn't appear to be related to systems programming.

gmfawcett 6y ago
I didn't mention "nil" in a simple example. I wasn't the poster of that comment.
- Isomorpheus 6y ago
  Oh, thought you were same poster. Well, that other person mentioned it in a context which doesn't appear to be related to systems programming. Just checked Github for some of the top Nim projects. Forum software: https://github.com/nim-lang/nimforum/search?q=nil&unscoped_q=nil https://github.com/nim-lang/nimforum/search?q=nil&unscoped_q... Web framework: https://github.com/planety/prologue/search?q=nil&unscoped_q=nil https://github.com/planety/prologue/search?q=nil&unscoped_q=... Twitter front-end: https://github.com/zedeus/nitter/search?q=nil&type=Code https://github.com/zedeus/nitter/search?q=nil&type=Code These uses of "nil" don't appear to have anything to do with systems programming.
  - gmfawcett 6y ago
    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.
    - Isomorpheus 6y ago
      Thanks for the honest reply. Nim interests me but this nil business seems questionable to me. Just found this comment from the language creator, https://github.com/nim-lang/Nim/issues/6638#issuecomment-487633727 https://github.com/nim-lang/Nim/issues/6638#issuecomment-487... "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." Seems a bit dismissive to me
      - gmfawcett 6y ago
        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.
        Isomorpheus 6y ago
        Thanks, I intend to give it a fair try
        elcritch 6y ago
        P.S., you can annotate procedure to help ensure you can’t raise certain conditions in code. Imho it’s nice for writing sections of “safe” code.
      - mratsim 6y ago
        `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: - https://nim-lang.org/docs/drnim.html https://nim-lang.org/docs/drnim.html The first use-case will be proving array bounds at compile-time and elide them. Future use-cases include not nil tracking.