Trouble with multiline if statments in OCaml

Question

I wasn't able to find a clear answer on Google, but it seems multiline if-statements are discouraged in OCaml (?) The ones I see with multiple lines seem to have begin end keywords in them.

I'm currently getting this error on the line num = (num - temp) / 10, characters 25-27 : Error: Parse error: "end" expected after [sequence] (in [expr]). If I remove all of the begin end then I get the error Error: This expression has type bool but an expression was expected of type int at the same line.

let rec reverse_int num =
  if num / 10 == 0 then begin
    num
  end else begin
    let temp = num mod 10 in
    num = (num - temp) / 10

    let numDigits = string_of_int num

    temp * (10 * String.length(numDigits)) + reverse_int num
  end;;

Answer 1

You probably mean something like the following.

let rec reverse_int num =
  if num / 10 == 0 then begin
    num
  end else begin
    let temp = num mod 10 in
    let num = (num - temp) / 10 in

    let numDigits = string_of_int num in

    temp * (10 * String.length(numDigits)) + reverse_int num
end;;

Problems here:

• line num = (num - temp) / 10 is a value of type boolean. What you mean is that you want, in what follows, num to have the new value (num - temp) / 10 and continue evaluation; hence replace this line with let num = (num - temp) / 10 in.

• lines let numDigits = string_of_int num temp * (10 * String.length(numDigits)) + reverse_int num are parsed let numDigits = string_of_int num temp *... which yields a type error, as the function string_of_int only has one argument. Here the in is necessary.