rec_fun_demo.ml

$ ocaml
# List.map (fun x -> let rec f x = match x with 0 -> 1 | n -> n * f (n - 1) in f x) [1; 2; 3];;
- : int list = [1; 2; 6]
# 
  let rec f x = match x with 0 -> 1 | n -> n * f (n - 1);;
val f : int -> int = <fun>
#                                                                                              
  List.map f [1; 2; 3];;                                                                       
- : int list = [1; 2; 6]
# 
  
  let rec f = function 0 -> 1 | n -> n * f (n - 1);;      
val f : int -> int = <fun>
# 
  List.map f [1; 2; 3];;                            
- : int list = [1; 2; 6]
#