Refactoring: move to call to [Arg.parse] into [main].

src/Engine.ml

@@ -1506,21 +1506,18 @@ let run_random ?timeout prologue fuel : int =
 
 (* -------------------------------------------------------------------------- *)
 
-(* Find the name of our input file on the command line. *)
+(* [main ?prologue fuel] parses the command line and starts testing. *)
 
-let source : string option =
+let main ?prologue:(prologue=ignore) fuel =
+
+  (* Parse the command line. *)
   let usage = sprintf "Usage: %s <input file>" Sys.argv.(0) in
   let source = ref None in
   Arg.parse [] (fun s -> source := Some s) usage;
-  !source
-
-(* -------------------------------------------------------------------------- *)
-
-(* Reading input data from the source file whose name was given on the command
-   line, perform a number of test runs. *)
 
-let main ?prologue:(prologue=ignore) fuel =
-  match source with
+  (* If a source file name was provided on the command line, enter AFL mode;
+     otherwise, enter random testing mode. *)
+  match !source with
   | Some source ->
       run_afl source prologue fuel
   | None ->