ocaml - Can't make exercise from Jason Hickey's "Introduction to Objective Caml" book -

i'm trying solve exercise:

suppose have function on integers f : int -> int mono- tonically increasing on range of arguments 0 n. is, f < f (i + 1) 0 ≤ < n. in addition f 0 < 0 , f n > 0. write function search f n finds smallest argument f ≥ 0.

now wrote this

let search f n =     let min = f 0 in let rec searchin =     if >= n min         else             if f min > f min =             searchin i+1;; 

but crashes error:

error: parse error: "in" expected after [binding] (in [expr])

what wrong? , implementation correct?

let search f n =     let min = f 0 in     let rec searchin =         if >= n min         else         if f min > f min = i;         searchin i+1 in searchin 0;; 

you forgot call function.

anyway false, correct search is

let search f n =   let rec searchin =     if i>=n failwith("error not possible")     else if f >0 i-1 else searchin (i+1)   in   searchin 0;; 

you can search loop

let search f n =     let = ref 0 in     while f (!i) < 0         i:= !i +1;     done; !i;;