How to process elements of an OCAML list?

Question

I want to process the data present in file "persons.txt". But i have tried everything to process all the lines from text file.

The only way i can process data is by creating the list manually.

let myList = ["John"; "23"]

I want the program to iterate through all the lines of the text file. I have managed a way to pass all the content of the text file into a list but i can+t seem to move on from that stage.

My way of thinking is:

1. Read content from text file
2. Convert to OCaml list
3. Separate list into sublists
4. Iterate through sublists
5. Only print to screen text respecting conditions

Can you please guide me?

Thanks!!

open Printf

(* FILE CONTENTS *)
(*
John;23;
Mary;16;
Anne;21;
*)

let file = "data/persons.txt"
;;

(* READ FROM EXTERNAL FILE *)
let read_lines name : string list =
  if Sys.file_exists (name) then
    begin
      let ic = open_in name in
      try
        let try_read () =
          try Some (input_line ic) 
          with End_of_file -> None 
        in
        let rec loop acc = 
          match try_read () with
          | Some s -> loop (s :: acc)
          | None -> close_in_noerr ic; List.rev acc 
        in
        loop []
      with 
        e -> close_in_noerr ic;[]
    end
  else
    []
;;

(...)

Answer 1

Your question is not at all clear. Here are some observations:

First, your read_lines function doesn't return the input in the form you need.

What read_lines returns looks like this:

["John;23;"; "Mary;16;"; "Anne;21;"]

But what you want is something more like this:

[("John", "23)"; ("Mary", "16"); ("Anne", "21")]

The key here is to split the strings into pieces using ; as a separator. You can probably use String.split_on_char for this.

Second, you are not defining a function to calculate an answer from paramters. Instead your calculation is based on global variables. This won't generalize.

Instead of saying this:

 let adult_check_condition = 
     ... using global age and name ...

You need to define a function:

let adult_check_condition age name =
     ... use parameters age and name ...

Then you can call this function with different ages and names.