When combined with lexically scoped closures, if you try to shadow your value bindings in a functional language and expect it to work the same way as mutating a variable does in an imperative language, you're in for a surprise.
Sure, you have to restrict the scope in which rebinding is legal, but I don't see how it's fundamentally any different than the use of a phi-node in SSA form.
val it = 1 : int // a is still bound to 1 as far as f() is concerned
Now in Javascript:
> var a = 1;
undefined
> function f(){return a};
undefined
> f();
1
> a = 2;
2
> f();
2
>
If you bind a val, then you define a function that references that val, then you later shadow the val binding, then call the function again, the function still sees the earlier val binding, because it's a closure of the environment at the point where the function was defined, not at the point where it was called. This is unlike variable assignment in imperative languages.
