open Lib;;
let x = "foo" in
x.[2] <- 'x';
if x.[2] <> 'x' then raise Not_found
;;

(**
       0 CONSTINT 42
       2 PUSHACC0 
       3 MAKEBLOCK1 0
       5 POP 1
       7 SETGLOBAL Lib
       9 GETGLOBAL "foo"
      11 PUSHCONSTINT 120
      13 PUSHCONST2 
      14 PUSHACC2 
      15 SETSTRINGCHAR 
      16 CONSTINT 120
      18 PUSHCONST2 
      19 PUSHACC2 
      20 GETSTRINGCHAR 
      21 NEQ 
      22 BRANCHIFNOT 29
      24 GETGLOBAL Not_found
      26 MAKEBLOCK1 0
      28 RAISE 
      29 POP 1
      31 ATOM0 
      32 SETGLOBAL T121-setstringchar
      34 STOP 
**)