return a list of lines in a file, with an optional skip number and max on actually returned ones

read_lines.ml

let read_lines ?skip ?maxn filename =
	let ic = open_in filename in
	let step,ctr = make_step_counter 0 in
	E.from_while begin fun () ->
		try 
			match skip,maxn with
			| (Some s, _)    when ctr () < s -> 
				ignore (input_line ic); step (); Some None 
			| (skip, Some n) when n > 0 && ctr () - (Option.default 0 skip) = n -> 
				close_in ic; None
			| _ -> 
				let line = input_line ic in step (); Some (Some line)
		with End_of_file -> None
	end |> 
	E.filter_map identity |> L.of_enum