report syntax error even with camlp4o

[agarwal]

We get different errors if #camlp4o is issued or not. IIUC, we are not catching the correct error when camlp4 is used.

Without camlp4o:

$ cat a.ml 
let x-plus-y = x + y;;

$ oloop a.ml
(* part 0 *)
# let x-plus-y = x + y;;
Error: Syntax error

With camlp4o:

$ cat a.ml 
#use "topfind";;
#camlp4o;;
let x-plus-y = x + y;;

$ oloop a.ml -silent-directives
(* part 0 *)
# #use "topfind";;

# #camlp4o;;

# let x-plus-y = x + y;;
Pervasives.Exit

Note the specific error also differs in OCaml's toplevel:

$ ocaml -noinit
        OCaml version 4.02.1

# let x-plus-y = x + y;;
Error: Syntax error

versus:

$ ocaml -noinit
        OCaml version 4.02.1

# #use "topfind";;
# #camlp4o;;
# let x-plus-y = x + y;;
Error: Parse error: [fun_binding] expected after [ipatt] (in [let_binding])