The ECLiPSe I/O is based on the concept of streams which are mapped on the I/O channels of the underlying operating system. Apart from user-definable streams there are several predefined system streams like toplevel_output, debug_input etc. which make it easy to filter the data of a certain kind, connect it with a windowing environment or to use it in event handlers. Any input stream can be passed as input to the compiler. Furthermore ECLiPSe supports I/O in raw mode and I/O to and from a string.