Constant space now grows automatically when needed. Each REPL now has its own working directory pathname and pathname defaults. Complete redesign of the error system. X11 graphics interface redesigned. Windows are now closed when they are reclaimed by the garbage collector.
New design supports ports that perform both input and output.
Ports now have better-defined control over blocking mode and terminal mode. Flushing of output buffers is not done automatically, except for the console port. New design is very similar to the Common Lisp pathname abstraction. Only strings and pathnames are valid. Representation of pathname directories changed to match Common Lisp.