duplicates:

• SR-2727 Script mode rules for top-level bindings are confusing and broken

Issue Description:

The following code snippet successful compiles and runs without infinite looping.

func foo() -> Int {
    return x
}
let x = foo()

It seems that `x` is uninitialized when returned from `foo` so `x` is assigned to an uninitiated value. In this example, printing `x` will output `0`, but if we change `Int` to a more complicated type like `[Int]`, printing will crash the program for obvious reasons.

I would expect this code to not compile since `x` is declared after `foo`. If it is intended to compile, then I think it ought to infinite loop. I definitely think the former behavior is much more intuitive than the latter.