In v5.0.99.7, when the plain Racket REPL is blocked waiting for input, it yields to GUI events. That's different from previous versions, which would leave the GUI frozen while waiting for REPL input.
More information the change: In v5.0.99.6, if you start plain Racket and load a GUI program like this, Welcome to Racket v5.0.99.6. > (require drracket) > then the GUI does not respond to any actions. The REPL blocks the main thread while waiting for input, and the main thread is also the event-handling thread, so no events get through. Now that Racket can run GUI programs at all, a stuck GUI when using the REPL seems likely to confuse and aggravate programmers. To solve this problem, the reading part of the REPL could be a separate thread from the main program. If reading is put in another thread, then the main thread could yield to GUI events while it waits for a expression read to complete. Meanwhile, putting the read in a separate thread should be ok; reading code is a different phase from running or even expanding code, and there shouldn't be races or interaction among the phases. Separating the REPL and GUI threads is exactly what `gracket -z' used to do. Adding a new layer of threads would be a significant change for plain Racket, however, and threads can create all sorts of unexpected problems. Even DrRacket doesn't really use a different thread for the interaction reader; it uses the syntax colorer to determine when input is ready. We don't want require syntax-coloring infrastructure or any similar extra layer in plain Racket. The solution in v5.0.99.7 is a parameter that allows a GUI `yield' to be interposed right where the REPL would block waiting for input. This interposition is implemented by wrapping the current input port with one that yields when no bytes are available. Wrapping a port is a somewhat roundabout way to make the REPL cooperate with GUIs, but it directly attacks the problem of blocking, doesn't introduce new threads, and accommodates readers for different languages. The new parameter is `current-get-interaction-input-port', which is used by the default prompt read handler, etc. The default function for the parameter returns the current input port. Invoking `racket/gui/base' installs a function that wraps the port to interpose a yield. Naturally, `gracket -z' now just uses `read-eval-print-loop' instead of `textual-read-eval-print-loop'. _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
