How to read a file, and write it to a different file - ocaml

Question

I hope all is well. At this point, I plan on reading a file, and then writing it to another file. (The equivalent of cp in OCaml, before I go ahead and manipulate text.) Currently in my code, I am making using the extlib to read a file, and then output it. I am also using dune to build file as an executable file. My file looks something like the following:
(* example.ml file *)
let read_filename = "example_1.ts"
let filename = "example_2.ts"
let () =
let text read_filename =
let chan = open_in read_filename in
Std.input_list chan
let filename = filename in
let text = text in
Std.output_file ~filename ~text
(* normal exit: all channels are flushed and closed *)
When I build the file using dune build example.bc I receive the following error:
File "example.ml", line 11, characters 2-5:
Error: Syntax error
I am trying to figure out what I am doing wrong, but to no avail. Any help would be more than appreciated. Thank you.

Answer 1

When I have readed you code I remark these lines.
let filename = filename in
let text = text in
Why have you writting this line ? (* You could delete it safely *)
And then I have found your syntax error was a line above you have forgotten a in
(* example.ml file *)
let read_filename = "example_1.ts"
let filename = "example_2.ts"
let () =
let text read_filename =
let chan = open_in read_filename in
Std.input_list chan
in
Std.output_file ~filename ~text
(* normal exit: all channels are flushed and closed *)
The rule for each local definition you must have a in keyword
(* a local definition is a let inside a let expression *)