This topic is covered in a sidebar in the chapter: allowing the top level to be list of statements instead of declarations means that each function definition must happen in order. Otherwise you can end up with troublesome code like this:
function f() { g() }
f()
var x = read_user_input()
function g() { print x }
Static languages typically don't allow the calls to f() and read_user_input() -- maybe that's the right answer here. There are other answers that come to mind as well. But, either way, I don't think we should perpetuate the mistake of dynamic variable lookup.
Ah, this is solved in OCaml using the 'and' keyword:
let rec even n =
match n with
| 0 -> true
| x -> odd (x-1)
and odd n =
match n with
| 0 -> false
| x -> even (x-1)
Although personally I've never liked the idiom where everything at the top-level is a statement. Even in OCaml I usually define a 'main' function, and call it at the bottom of the file:
let main args = do stuff...
...
let () = main Sys.argv
Yes, more specifically, the "let rec" is what begins the series of mutually recursive definitions. The "rec" is a clue that this is specifically for supporting this exact recursive case.
> Although personally I've never liked the idiom where everything at the top-level is a statement.
For statically-typed languages, I'm not a huge fan of it either. But for dynamically-typed ones, I think it works out OK.
