source, target = fs fs source-file-name 
                    ft target-file-name 
' fs = FS_REQUEST | FS_OPEN_IF_EXISTS | FS_RETURN_ON_ERROR | FS_READ,
  ft = FS_REQUEST | FS_REPLACE_IF_EXISTS | FS_RETURN_ON_ERROR | FS_WRITE

if (source && target) ->
  text = char-in source; - char-out target text
  ...
;
