(**
    Student modules using include module
*)

type grade = Pass | No_pass

let string_of_grade = function
    | Some Pass -> "Pass"
    | Some No_pass -> "No pass"
    | None -> "Not graded"

(**
    "Base-class"
*)
module Student = struct
    type student = {
        name : string;
        tests : int list;
        course_grade : grade option;
    }

    let make name = {
        name = name;
        tests = [];
        course_grade = None
    }

    let to_string s =
        Printf.sprintf "Student: %s; number of tests made: %d; course grade: %s"
            s.name
            (List.length s.tests)
            (string_of_grade s.course_grade)
end

module GraduateStudent = struct
    include Student
    let compute_course_grade s =
        let tests = s.tests in
        let total = List.fold_left (+) 0 tests in
        let grade = match total / List.length tests with
            | q when q >= 80 -> Pass    (* <-- 80 for grad *)
            | _ -> No_pass
        in
        {s with course_grade = Some grade}
end

module UndergraduateStudent = struct
    include Student
    let compute_course_grade s =
        let tests = s.tests in
        let total = List.fold_left (+) 0 tests in
        let grade = match total / List.length tests with
            | q when q >= 70 -> Pass    (* <-- 70 for undergrad *)
            | _ -> No_pass
        in
        {s with course_grade = Some grade}
end

type grad_students =
    | Grad of GraduateStudent.student
    | Undergrad of UndergraduateStudent.student

let _ =
    let student1 = GraduateStudent.make "Foo Barsson" in
    let student2 = UndergraduateStudent.make "J.R.R Tolkien" in

    let roster = [
        Grad student1;
        Undergrad student2;
    ] in

    List.iter (fun s ->
        print_endline (match s with
            | Grad s -> UndergraduateStudent.to_string s    (* <-- Don't want this to compile *)
            | Undergrad s -> UndergraduateStudent.to_string s
        )
    ) roster;

    ()