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Comment by rapala | Hacker News Reader

In a lexically scoped language I would assume that the scoping follows the lexical representation of the code. The given example goes against this assumption. The variable i is not even defined before it is refered to in the inner function.

The level of scope (global, block, ...) interact with the type of scoping in many ways, so I would not say that they are orthogonal. This example would behave very differently under dynamic and lexical scoping.

  function foo() {
    var i = 1;
    function bar() {
        var a = i;
        var i = 2;
        return a + i;
    }
    return bar;
  }
  foo()() // => ?

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    In a lexically scoped language I would assume that the scoping follows the lexical representation of the code.

In a lexically scoped language the variables belong to the containing lexical scope. That that lexical scope can be a function rather than a block doesn't make Javascript any less lexically scoped (in cases other than the dynamic this).

    The variable i is not even defined before it is refered to in the inner function.

The order that variables appear within a scope has no effect on the scoping rules. For example, in C#:

    void Foo() {
        i = 10;
        int i;
    }

Gives "error CS0841: Cannot use local variable 'i' before it is declared". It knows exactly what variable "i = 10" is referring to because it's declared in the same scope, but the language designers have decided to add the rule that you're not allowed to reference it before it's declared (because doing so is most likely a bug).

Incidentally, Javascript made the opposite decision; you can refer to variables before their declaration, they're just "undefined". But in both cases the compiler knows what "i" it's referring to by the lexical scope.

I would argue that the order of declarations is part of the scoping rules. In your example the variable i is not yet in scope when the assignment is done, and thus the compiler complaints. But this is of course somewhat philosophical.

My first argument was that the order of statements is part of the lexical representation of code, and thus should effect the lexical scoping.

I'd say the order of declarations isn't part of the scoping rules. The scoping rules are used for name resolution. In my example, both i's belong to the same scope, so the name resolution says "oh, that first i is the one in this scope, not any parent scope".

In languages like C#, a separate analysis is then done to find out if the variable is definitely assigned at each reference. This can include some sophisticated reachability analysis(how sophisticated depends on the usefulness/complexity tradeoff).

I guess it's all semantics really, but I prefer to keep the scope (ha ha) of lexical scoping rules closer to name resolution than start mixing in definite assignment and reachability analysis and the things that come with that.

It makes understanding and expressing the commonalities and differences between different language's lexical scoping a lot easier. C# is lexically scoped with blocks introducing new lexical scopes. Javascript* and Python are lexically scoped with functions introducing new lexical scopes. As an orthogonal concept, C# and Python disallow references before definite assignment, while Javascript allows it.

(*) With the dynamic 'this' caveat.

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