tasks a-s

Task/Queue-Definition/OCaml/queue-definition-1.ocaml

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+module FIFO : sig
+  type 'a fifo
+  val empty: 'a fifo
+  val push: fifo:'a fifo -> item:'a -> 'a fifo
+  val pop: fifo:'a fifo -> 'a * 'a fifo
+  val is_empty: fifo:'a fifo -> bool
+end = struct
+  type 'a fifo = 'a list * 'a list
+  let empty = [], []
+  let push ~fifo:(input,output) ~item = (item::input,output)
+  let is_empty ~fifo =
+    match fifo with
+    | [], [] -> true
+    | _ -> false
+  let rec pop ~fifo =
+    match fifo with
+    | input, item :: output -> item, (input,output)
+    | [], [] -> failwith "empty fifo"
+    | input, [] -> pop ([], List.rev input)
+end

Task/Queue-Definition/OCaml/queue-definition-2.ocaml

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+# open FIFO;;
+# let q = empty ;;
+val q : '_a FIFO.fifo = <abstr>
+# is_empty q ;;
+- : bool = true
+# let q = push q 1 ;;
+val q : int FIFO.fifo = <abstr>
+# is_empty q ;;
+- : bool = false
+
+# let q =
+    List.fold_left push q [2;3;4] ;;
+val q : int FIFO.fifo = <abstr>
+
+# let v, q = pop q ;;
+val v : int = 1
+val q : int FIFO.fifo = <abstr>
+# let v, q = pop q ;;
+val v : int = 2
+val q : int FIFO.fifo = <abstr>
+# let v, q = pop q ;;
+val v : int = 3
+val q : int FIFO.fifo = <abstr>
+# let v, q = pop q ;;
+val v : int = 4
+val q : int FIFO.fifo = <abstr>
+# let v, q = pop q ;;
+Exception: Failure "empty fifo".