basic functions in Enum

enum.ml

@@ -34,12 +34,26 @@ and 'a generator = unit -> 'a
   (** A generator may be called several times, yielding the next value
       each time. It raises EOG when it reaches the end. *)
 
+let empty () = fun () -> raise EOG
+
+let singleton x =
+  fun () ->
+    let stop = ref false in
+    fun () ->
+      if !stop
+        then raise EOG
+        else begin stop := true; x end
+
 let start enum = enum ()
 
 let next gen = gen ()
 
 let junk gen = ignore (gen ())
 
+let is_empty enum =
+  try ignore ((enum ()) ()); false
+  with EOG -> true
+
 let fold f acc enum =
   let rec fold acc gen =
     let acc', stop =

enum.mli

@@ -37,6 +37,12 @@ and 'a generator = unit -> 'a
   (** A generator may be called several times, yielding the next value
       each time. It raises EOG when it reaches the end. *)
 
+val empty : 'a t
+  (** Enmpty enum *)
+
+val singleton : 'a -> 'a t
+  (** One-element enum *)
+
 val start : 'a t -> 'a generator
   (** Create a new generator *)
 
@@ -46,6 +52,9 @@ val next : 'a generator -> 'a
 val junk : 'a generator -> unit
   (** Drop element *)
 
+val is_empty : _ t -> bool
+  (** Check whether the enum is empty *)
+
 val fold : ('b -> 'a -> 'b) -> 'b -> 'a t -> 'b
   (** Fold on the generator *)