[arocks]

It seems `int_of_float` and `float_of_int` are deprecated by the Jane Streets Core library. It even throws errors on utop. I believe they need to be replaced by `Int.of_float` and `Float.of_int` respectively.

EDIT: Some more corrections:

1. `List.hd []` doesn't raise an error as its return type is an option. So the result is a `None`.

2. `List.map` and `List.filter` arguments should be reversed. First argument should be a list and the second should be the mapping function.

[fredyr]

The code examples doesn't use Jane Streets Core as the primary standard library. If you do, for example by adding `open Core.Std` to your .ocamlinit, you'll get the behaviour you're describing.

It is probably a good idea to use Core, but for this introduction I wanted as little requirements as possible.

edit: spelling

[arocks]

Right. Since you mention the installation instructions from Real World OCaml and the examples in the book need you to use Core, it is likely that beginners would experience these issues.

[fredyr]

That's a good point. I'll add a note to explicitly say that the examples doesn't use Core.