I'm sure this is a basic question:

what is the difference between these ways of defining a function, and 
what is the most efficient (I mean for the resulting function f = binop 
o f1 f2, which typically will be called x*1000 times)

type operator = Plus | Minus;;


let binop1 o f1 f2 =
   fun x -> match o with
	| Plus -> (f1 x) +. (f2 x)
	| Minus -> (f1 x) -. (f2 x)

let binop2 o f1 f2 =
   match o with
	| Plus -> fun x -> (f1 x) +. (f2 x)
	| Minus -> fun x -> (f1 x) -. (f2 x)

let binop3 o f1 f2 =
   let op = match o with
	| Plus ->  (+.)
	| Minus -> (-.) in
	fun x -> op (f1 x) (f2 x)

let binop4 o f1 f2 =
   fun x ->
     let op = match o with
	| Plus ->  (+.)
	| Minus -> (-.) in
       	op (f1 x) (f2 x)

Thanks for your expertise !

San