Syntax error from ocaml reading standard input

Question

For some reason if I put these functions one by one in utop it works, but if I process them all I got a Syntax error (without anything other insight about what might be wrong).

let rec solve = function
  | [] -> print_string("")
  | a::b -> print_string(a); solve b

let rec read_input acc = function
  | 0 -> acc
  | n -> let s = read_line() in
    read_input (s::acc) (n-1)

let n = read_int() in
let inp = read_input [] n in
solve inp

Answer 1

For me, OCaml points to a syntax error on the first in in the following (I have made formatting a little more conventional):

let n = read_int() in
let inp = read_input [] n in
solve inp;;

Keep in mind that the expression shown above is an expression. Coming where it does after the previous binding causes a syntax error. Let's make it work by making it yet another toplevel binding.

let rec solve = function
  | [] -> print_string("")
  | a::b -> print_string(a); solve b

let rec read_input acc = function
  | 0 -> acc
  | n -> let s = read_line() in
    read_input (s::acc) (n-1)

let () =
  let n = read_int() in
  let inp = read_input [] n in
  solve inp

As a side note, using the |> operator can make this a bit more concise.

let () =
  read_int () 
  |> read_input [] 
  |> solve

Also it strikes me than read_input is returning the list in the wrong order:

utop # read_input [] 2;;
3
4
- : string list = ["4"; "3"]

Maybe you wanted to reverse your accumulator.

let rec read_input acc = function
  | 0 -> List.rev acc
  | n -> let s = read_line () in
    read_input (s::acc) (n-1)

Or even:

let read_input n = 
  List.init n (fun _ -> read_line ())