component PrefixFile(prefix, file) -> out {
  filename : std.Constant(data=file)
  file : io.FileReader()
  prep : text.PrefixString(prefix=prefix)

  filename.token > file.filename
  file.out > prep.in
  prep.out > .out
}

src : PrefixFile(prefix="?--- ", file="data.txt")
snk : io.Print()

src.out>snk.token
