add CCFun.(let@) (if OCaml >= 4.08)

src/core/CCFun.ml

@@ -85,10 +85,16 @@ let rec iterate n f x =
 
 module Infix = struct
   (* default implem for some operators *)
-  let ( |> ) x f = f x
-  let ( @@ ) f x = f x
+  let ( |> ) = CCShims_.Stdlib.( |> )
+  let ( @@ ) = CCShims_.Stdlib.( @@ )
   let ( %> ) = compose
-  let ( % ) f g x = f (g x)
+  let[@inline] ( % ) f g x = f (g x)
+
+  [@@@ifge 4.8]
+
+  let ( let@ ) = ( @@ )
+
+  [@@@endif]
 end
 
 include Infix
@@ -99,7 +105,8 @@ end) =
 struct
   type 'a t = X.t -> 'a
 
-  let return x _ = x
-  let ( >|= ) f g x = g (f x)
-  let ( >>= ) f g x = g (f x) x
+  let[@inline] return x _ = x
+  let[@inline] ( >|= ) f g x = g (f x)
+  let[@inline] ( >>= ) f g x = g (f x) x
 end
+[@@inline]

src/core/CCFun.mli

@@ -9,6 +9,8 @@ include module type of Fun
 
 [@@@else_]
 
+(* port from stdlib *)
+
 external id : 'a -> 'a = "%identity"
 (** This is an API imitating the new standard Fun module *)
 
@@ -99,6 +101,15 @@ module Infix : sig
 
   val ( % ) : ('b -> 'c) -> ('a -> 'b) -> 'a -> 'c
   (** [(f % g) x] or [(%) f g x] is [f (g x)]. Mathematical composition. *)
+
+  [@@@ifge 4.8]
+
+  val ( let@ ) : ('a -> 'b) -> 'a -> 'b
+  (** [let@ x = foo in bar] is the equivalent of [foo @@ fun x -> bar].
+      It can be very useful for resource management, alongside with {!protect}.
+      @since NEXT_RELEASE *)
+
+  [@@@endif]
 end
 
 include module type of Infix