Reorganize code and document functions

lib/dune

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+(library
+ (name inspector))

lib/repl.ml

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+let rec loop state =
+  print_string "inspector> ";
+  flush stdout;
+  try
+    match read_line () |> String.lowercase_ascii with
+    | "exit" | "quit" -> print_endline "bye"
+    | "next" -> loop (State.next state)
+    | "prev" -> loop (State.prev state)
+    | "show" ->
+        Printf.printf "[%d]: %s\n" (State.cursor state) (State.show_line state);
+        loop state
+    | str ->
+        print_endline str;
+        loop state
+  with End_of_file -> print_endline "bye"

lib/repl.mli

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+(** Interactive command loop for the inspector.
+
+    The REPL (Read–Eval–Print Loop) repeatedly reads commands from standard
+    input and applies them to the current navigation state.
+
+    Each command may update the state (for example moving the cursor) or display
+    information about the current log line.
+
+    The loop continues until the user enters ["quit"] or ["exit"], or until an
+    end-of-file condition is encountered on standard input (for example when
+    pressing Ctrl-D). *)
+
+val loop : State.t -> unit
+(** [loop state] starts the interactive command loop.
+
+    The given [state] represents the current navigation state of the loaded log
+    file. Commands executed by the user may derive new states (for example via
+    {!State.next} or {!State.prev}) which are then used in the next iteration of
+    the loop.
+
+    The function runs until the user exits the program. *)

lib/state.ml

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+type t = { lines : string array; cursor : int }
+(** Invariant: cursor >= 0 cursor < Array.length lines *)
+
+let size s = Array.length s.lines
+let cursor s = s.cursor
+
+let create (fname : string) : t =
+  let lines =
+    In_channel.with_open_text fname In_channel.input_lines |> Array.of_list
+  in
+  { lines; cursor = 0 }
+
+let show_line s : string = s.lines.(s.cursor)
+
+let next s =
+  if s.cursor < size s - 1 then { s with cursor = s.cursor + 1 } else s
+
+let prev s = if s.cursor > 0 then { s with cursor = s.cursor - 1 } else s

lib/state.mli

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+type t
+(** Log navigation state.
+
+    A [t] represents a loaded log file and a cursor pointing to the currently
+    active line. *)
+
+val create : string -> t
+(** [create file] loads the log file into memory and initializes the cursor at
+    the first line. *)
+
+val show_line : t -> string
+(** [show_line s] returns the line currently pointed to by the cursor. *)
+
+val next : t -> t
+(** [next s] moves the cursor to the next line if possible. *)
+
+val prev : t -> t
+(** [prev s] moves the cursor to the previous line if possible. *)
+
+val cursor : t -> int
+(** Current cursor position. *)
+
+val size : t -> int
+(** Number of lines in the log. *)