code: @CanIgnoreReturnValue // some processors won't return a useful result
    public static <T> T readLines(File file, Charset charset, LineProcessor<T> callback)
        throws IOException {
      return asCharSource(file, charset).readLines(callback);
    }
docs: Streams lines from a {@link File}, stopping when our callback returns false, or we have read
  all of the lines.
  
  @param file the file to read from
  @param charset the charset used to decode the input stream; see {@link StandardCharsets} for
  helpful predefined constants
  @param callback the {@link LineProcessor} to use to handle the lines
  @return the output of processing the lines
  @throws IOException if an I/O error occurs