on-execute in drscheme:language:language<%>

The on-execute method is called on DrScheme's eventspace's main thread before any evaluation happens during execution. Use this method to initialize MzScheme's parameters for the user. When this function is called, the user's thread has already been created, as has its custodian. These parameters have been changed from the defaults in MzScheme:

• current-custodian is set to a new custodian.

• current-namespace has been set to a newly created empty namespace.This namespace has the following modules copied (with namespace-attach-module) from DrScheme's original namespace:

  • 'mzscheme

  • '(lib "mred.ss" "mred")

• read-curly-brace-as-paren is #t,

• read-square-bracket-as-paren is #t,

• The port-write-handler and port-display-handler have been set to procedures that call pretty-print and pretty-display instead of write and display. When pretty-print and pretty-display are called by these parameters, the pretty-print-columns parameter is set to 'infinity, so the output looks just like write and display. This is done so that special scheme values can be displayed as snips.

• The current-print-covert-hook is to a procedure so that snip%s are just returned directly to be inserted into the interactions text% object.

• The output and input ports are set to point to the interactions window with these parameters: current-input-port, current-output-port, and current-error-port.

• The event-dispatch-handler is set so that DrScheme can perform some initial setup and close down around the user's code.

• The current-directory and current-load-relative-directory are set to the directory where the definitions file is saved, or if it isn't saved, to the initial directory where DrScheme started up.

• The snip-class-list, returned by get-the-snip-class-list is initialized with all of the snipclasses in DrScheme's eventspace's snip-class-list.

• The error-print-source-location parameter is set to #f and the error-display-handler is set to a handler that creates an error message from the exception record, with font and color information and inserts that error message into the definitions window.

The run-in-user-thread arguments accepts thunks and runs them on the user's eventspace's main thread. These thunks must not raise an exceptions (or drscheme itself will get stuck). In addition, the output ports are not yet functioning, so print outs should be directed to the original drscheme output port, if necessary.

• (send a-drscheme:language:language on-execute settings run-in-user-thread) -> any
     settings : settings
     run-in-user-thread : ((-> any) -> any)