CODEWITHSUNDEEP
splitstreamocaml
AC-5
AC-5

Reputation: 293

OCaml - Reading from file and splitting on character

I'm trying to read from a file in OCaml and break each line into a list of strings delimited by spaces and then append that list to a cumulative list. The error I'm receiving is:

File "bin/scanner.ml", line 17, characters 25-42: Error: This expression has type string list but an expression was expected of type unit

My entire program (scanner.ml) is:

  1 let tokens = [];;
  2 
  3 let split_spaces line =
  4     (String.split_on_char ' ' line) @ tokens;
  5     ;;
  6 
  7 (* Read input from an external file *)
  8 let line_stream_of_channel channel =
  9     Stream.from
 10         (fun _ ->
 11             try Some (input_line channel) with End_of_file -> None)
 12     ;;
 13 
 14 let in_channel = open_in "./input_files/test.c" in
 15     try
 16         Stream.iter
 17             (fun line -> split_spaces line)
 18         (line_stream_of_channel in_channel);
 19         close_in in_channel
 20     with e ->
 21         close_in in_channel;
 22         raise e
 23     ;;

I think I understand that the error is that split_space returns a list of strings while the anonymous function in line 17 expects a function returning type unit. What I am stuck on is how I can modify split_spaces so that its return type is unit.

Upvotes: 0

Views: 668

Answers (1)

Jeffrey Scofield
Jeffrey Scofield

Reputation: 66803

A function that returns unit is an imperative-style function that does something for its side effect and doesn't return a useful value.

If your functions all return unit, how will you accumulate your list of words?

In fact I don't see this cumulative list of words anywhere in your code.

The fact is you probably want to go the other way. You want to replace Stream.iter, which is an imperative function with side effects. Instead you most likely want your own function that calls Stream.next and returns an accumulated value (rather than unit).

Upvotes: 1

Related Questions