The interpreter uses the console for its I/O; no fancy windows or anything. When possible, it uses the GNU readline interface for its input.
$ /usr/local/bin/psyche Psyche version X.Y, Copyright (C) 2002 Y. Duppen Psyche comes with ABSOLUTELY NO WARRANTY. This is free software, and you are welcome to redistribute it under certain conditions; read the attached COPYING for details. psyche> (define x 5) psyche> (define (square n) ......> (* n n)) psyche> (square x) 25 psyche> (square 4) 16 psyche> (square "hello") Error: unsupported operand type(s) for *: 'str' and 'str' psyche> (quit) $