Notes from Real World OCaml, chapters 4 and 5

Chapter 4

Chapter 4 mostly works, but you need to replace open Core.Std with open Core, and include open Base.Poly after open Core in session_info.ml. This latter change restores the polymorphic equality operators. My updated code from it at the end of the chapter is here.

Chapter 5

Instead of using Core_extended, which appears to be a mere shadow of itself, you should install the shell package. This appears to be the Shell module from Core_extended broken out to its own package. Thus, in utop, instead of:

utop # #require "core_extended";;
utop # open Core_extended.Std;;

Run this instead:

utop # #require "shell";;
utop # open Core;;

For the example, here’s the code:

type host_info = {
  hostname : string;
  os_name : string;
  cpu_arch : string;
  timestamp : Core.Time.t;
}

let my_host =
  let sh = Shell.sh_first_line_exn in {
    hostname = sh "hostname";
    os_name = sh "uname -s";
    cpu_arch = sh "uname -p";
    timestamp = Core.Time.now ();
  }

Notice how I’ve substituted sh_first_line_exn for sh_one_exn? The latter is deprecated, but the former has the same behaviour but is not deprecated.

For host_info_to_string, you’ll need to do open Printf to include sprintf in the REPL’s namespace.

For the get_users function, it tells you to add with fields at the end of the Login module. This no longer works. Instead, you need the ppx_jane package, which appears to have superceded fieldslib for this purpose, and rather than the with fields, you put the annotation [@@deriving fields] after the type. ppx_janne should already be installed as a dependency previously. Recember that if you want its contents available within utop, you’ll need to run #require "ppx_jane". If you don’t, the annotation won’t result in any code being generated.