restructure + lecutre 07

lectures/04/notes.ml

@@ -0,0 +1,107 @@
+(* Some, None - Are called data/value constructors *)
+Some 1;; (* - : int option = Some 1 *)
+
+None;; (* - : 'a option = None *)
+
+(* OPTIONS are called type constructors, it takes a type *)
+(* 'a is a type variable, where 'a is some type such as int *)
+
+type 'a option = None | Some of 'a;;
+
+(*
+  You can define any type you want, this type constructor starts
+  with a lower case letter "direction" and the value constructor starts
+  with uppercase "North", "East", ... 
+
+  type constructors are not functions
+*)
+type direction = North | East | South | West;;
+
+(* There are RESULT types *)
+Ok 1;;
+Error "hell";; (* albert's example is hell not my example *)
+
+(*
+  A result is a two type variable, this is the syntax for
+  something that takes to type variables
+*)
+type ('a, 'b) result = Ok of 'a | Error of 'b;;
+
+(1, 2);; (* type is - : int * int = (1, 2) *)
+(* (int, int) : (type * type) *)
+
+(* we define an expresion that has a type of Int, and can be of type Add, Sub or Mul *)
+type expr = 
+    Int of int
+  | Add of expr * expr
+  | Sub of expr * expr
+  | Mul of expr * expr;;
+
+(* We then define an eval function, that takes in an eval,
+   and recursively evaluates e1, e2 till they are just of
+   type Int to then evaluate the addition, subtraction, etc. *)
+let rec eval = function
+  | Int n -> n
+  | Add (e1, e2) -> eval e1 + eval e2
+  | Sub (e1, e2) -> eval e1 - eval e2
+  | Mul (e1, e2) -> eval e1 * eval e2;;
+
+let e = Mul(Add (Int 1, Int 2), Int 7);;
+eval e;;
+
+(* lets apply the type variables and constructors to create a card type *)
+type suit = Club | Diamond | Heart | Spade;;
+type rank = Num of int | Jack | Queen | King | Ace;;
+type card = rank * suit;;
+
+let compare_rank r1 r2 = 
+  match r1, r2 with
+  | Num x, Num y -> Int.compare x y
+  | Num _, _ -> -1
+  | _, Num _ -> 1
+  | _, _ -> Stdlib.compare r1 r2;;
+
+let compare_suit s1 s2 = Stdlib.compare s1 s2;;
+
+let compare_card (r1, s1) (r2, s2) =
+  let c = compare_rank r1 r2 in
+  if c = 0 then compare_suit s1 s2
+  else c;;
+
+let string_of_suit = function
+  | Club -> "clubs"
+  | Diamond -> "diamonds"
+  | Heart -> "hearts"
+  | Spade -> "spades";;
+
+let string_of_rank = function
+  | Num n -> string_of_int n
+  | Jack -> "Jack"
+  | Queen -> "Queen"
+  | King -> "King"
+  | Ace -> "Ace"
+
+let string_of_card (r, s) =
+  string_of_rank r ^ " of " ^ string_of_suit s;;
+
+compare_card (King, Diamond) (Queen, Heart);;
+string_of_card (Queen, Heart);;
+
+let all_suits = [Club; Diamond; Heart; Spade];;
+let all_ranks =
+  (List.init 9 (fun x -> x + 2) |> List.map (fun x -> Num x)) @ 
+  [Jack; Queen; King; Ace];;
+
+let all_cards =
+  List.fold_right (fun rank acc -> (
+    List.fold_right (fun suit acc -> (rank, suit) :: acc) all_suits []
+  ) @ acc) all_ranks [];;
+
+type 'a linked_list = Nil | Cons of 'a * 'a linked_list;;
+
+let rec map_linked f = function
+  | Nil -> Nil
+  | Cons (x, l) -> Cons (f x, map_linked f l);;
+
+Cons (1, Cons (2, Cons (3, Nil))) |> map_linked (fun x -> x * x);;
+