1 files changed, 74 insertions, 0 deletions
diff --git a/src/nbc/sequence.sml b/src/nbc/sequence.sml
new file mode 100644
index 0000000..73a3fbf
--- /dev/null
+++ b/src/nbc/sequence.sml
@@ -0,0 +1,74 @@
+signature SEQUENCE = sig
+	type 'a t
+	val fold: ('a * 'b -> 'b) -> 'b -> 'a t -> 'b
+	val from: (unit -> 'a option) -> 'a t
+	val map: ('a -> 'b) -> 'a t -> 'b t
+	val app: ('a -> unit) -> 'a t -> unit
+	val fromArray: 'a array -> 'a t
+	val fromList: 'a list -> 'a t
+	val toList: 'a t -> 'a list
+	val toArray: 'a t -> 'a array
+end
+
+structure Sequence :> SEQUENCE = struct
+	type 'a t = unit -> 'a option
+	fun fold f seed t =
+		let
+			fun loop x =
+				case t () of
+					NONE => x
+					| SOME y => loop (f (y, x))
+		in
+			loop seed
+		end
+	fun from t = t
+	fun map f t =
+		fn () => (
+			case t () of
+				NONE => NONE
+				| SOME x => SOME (f x)
+		)
+	fun app f t =
+		let
+			fun loop () =
+				case t () of
+					NONE => ()
+					| SOME x => (
+						f x
+						; loop ()
+					)
+		in
+			loop ()
+		end
+	fun fromArray a =
+		let
+			val i = ref 0
+			fun f () =
+				if !i >= Array.length a then NONE
+				else
+					SOME (Array.sub (a, !i))
+					before i := !i + 1
+		in
+			from f
+		end
+	fun fromList l =
+		let
+			val c = ref l
+			fun f () =
+				case !c of
+					x :: y => (c := y; SOME x)
+					| nil => NONE
+		in
+			from f
+		end
+	fun toList t =
+		let
+			fun loop l =
+				case t () of
+					NONE => rev l
+					| SOME x => loop (x :: l)
+		in
+			loop nil
+		end
+	fun toArray t = Array.fromList (toList t)
+end