add CCOpt.if_

src/core/CCOpt.ml

@@ -71,6 +71,8 @@ let filter p = function
   | Some x as o when p x -> o
   | o -> o
 
+let if_ p x = if p x then Some x else None
+
 let exists p = function
   | None -> false
   | Some x -> p x

src/core/CCOpt.mli

@@ -50,6 +50,10 @@ val filter : ('a -> bool) -> 'a t -> 'a t
 (** Filter on 0 or 1 element
     @since 0.5 *)
 
+val if_ : ('a -> bool) -> 'a -> 'a option
+(** [if_ f x] is [Some x] if [f x], [None] otherwise
+    @since NEXT_RELEASE *)
+
 val exists : ('a -> bool) -> 'a t -> bool
 (** @since NEXT_RELEASE *)