TODO

- Fully qualify all anonymous functions
- Qualify symbols to their corresponding package instead of "main".
- Module system, imports/exports
  - Scope identifiers to their corresponding modules. Otherwise they override
    each other. The code below results in the compiled output below it. Notice
    how two "main.message" local variables initialized. Correct values but
    incorrectly named.

    // Module1.bb
    module Module1
    import Module2 exposing (print_message)
    def message = "from module 1"
    print_message()

    // Module2.bb
    module Module2
    import Prelude exposing (println)
    def message = "from module 2"
    def print_message() = println(message)

    // Output
    main:
        push      Const, str-2
        store     I32, main.message
        push      Const, str-4
        store     I32, main.message
        ...
    main.print_message:
        ...
        load      Str, main.message
        call      main.println
        ...
    .Str str-2: from module Prelude
    .Str str-4: from module 1

- Parsing errors:
    - astOf("3 + 1 / 4 * 1 + 9") shouldEqual "(+ (+ 3 (/ 1 (* 4 1))) 9)"
                           shouldReallyEqual "(+ (+ 3 (* (/ 1 4) 1)) 9)"

    - it should "correctly order operator with equal precedence 2" in {
        astOf("1 + 2 / 1 * 5") shouldEqual "(+ 1 (* (/ 2 1) 5))"
      }

    - it should "correctly order operator with equal precedence 4" in {
        astOf("1 + 2 / 1 * 5 + 7") shouldEqual "(+ (+ 1 (* (/ 2 1) 5)) 7)"
      }