Hi all,
   I have a question simplified as below:

 let rec fib = fun x -> fib (x - 1);;                                                                                                                       
val fib : int -> 'a = <fun>                                                                                                                                  
# let rec fib = (Obj.magic (fun x -> fib (x - 1)) : int -> 'a);;                                                                                             
Characters 15-47:                                                                                                                                            
  let rec fib = (Obj.magic (fun x -> fib (x - 1)) : int -> 'a);;                                                                                             
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                            
Error: This kind of expression is not allowed as right-hand side of `let rec'  

I know `fib` is a legal expression, is there any way to work around it?
 Thanks -- Hongbo