What are you trying to accomplish exactly?
What type do you want fib to have?

I usually use lazy and force to get around let rec limitations and that
usually allows for only local uglyness, the lazy types usually don't escape.
>
> On Jul 12, 2016 5:37 PM, "Hongbo Zhang (BLOOMBERG/ 731 LEX)" <
hzhang295@bloomberg.net> wrote:
>>
>> 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