Jane Street OCaml Challenge: Records
Records in OCaml are named collections of fields, similar to structs or classes in other languages.
Defining and Using a Record
type person = {
age : int;
first_name : string;
last_name : string;
number_of_cars : int;
} [@@deriving compare]
let an_example : person = {
first_name = "Cotton-eyed";
last_name = "Joe";
age = 22;
number_of_cars = 0;
}
let age : int = an_example.age
let () = assert (age = 22)
Pattern Matching and Field Access
let print_info {first_name; last_name; age; number_of_cars} =
Stdio.print_endline first_name;
Stdio.print_endline last_name;
Stdio.printf "Age: %d, # of cars: %d\n" age number_of_cars
let print_name {first_name; last_name; age = _; number_of_cars = _} =
Stdio.print_endline first_name;
Stdio.print_endline last_name
Functional Record Updates
Use with to copy and update fields:
let add_one_to_age person = { person with age = person.age + 1 }
let () = assert ((add_one_to_age an_example).age = 23)
Your Turn: Modify a Person
If first_name = "Jan", return a new person with age set to 30. Otherwise, increase number of cars by 6.
let modify_person (person : person) =
failwith "For you to implement"
Tests
module For_testing = struct
let test_ex1 : person = {
first_name = "Jan";
last_name = "Saffer";
age = 55;
number_of_cars = 0;
}
let test_ex1' : person = {test_ex1 with age = 30}
let test_ex2 : person = {
first_name = "Hugo";
last_name = "Heuzard";
age = 4;
number_of_cars = 55;
}
let test_ex2' : person = { test_ex2 with number_of_cars = 61 }
let%test "Testing modify_person..." =
[%compare.equal: person] test_ex1' (modify_person test_ex1)
let%test "Testing modify_person..." =
[%compare.equal: person] test_ex2' (modify_person test_ex2)
end