uses io.InputStream, io.OutputStream

interface FileOutput extends OutputStream {
    close()
}
interface FileInput extends InputStream {
    close()
}

read(filename: string): FileInput
  // Open the named file for reading.  Return null on failure.
create(filename: string): FileOutput
  // If the file does not exist, create it and return a FileOutput that
  // will write to the file.  If the file cannot be created, return null.
append(filename: string): FileOutput
  // If the file can be opened, return a FileOutput that appends to it.
  // Otherwise, return null.
remove(filename: string): bool
  // Remove the file and return true if successful