2 Implementing DrRacket Plugins🔗ℹ

Plugins are designed for major extensions in DrRacket’s functionality. To extend the appearance or the functionality the DrRacket window (say, to annotate programs in certain ways or to add buttons to the DrRacket frame) use a tool. The Macro Stepper, the Syntax Checker, the Stepper, and the teaching languages are all implemented as tools.

This bitmap and the name show up in the about box, the bug report form, and the splash screen as the tool is loaded at DrRacket’s startup.

Each of the drracket-tools files must contain a module that provides tool@, which must be bound to a unit. The unit must import the drracket:tool^ signature, which is provided by the drracket/tool library. The drracket:tool^ signature contains all of the names listed in this manual. The unit must export the drracket:tool-exports^ signature.

If the tool raises an error as it is loaded, invoked, or as the phase1 or phase2 thunks are called, DrRacket catches the error and displays a message box. Then, DrRacket continues to start up, without the tool.

Finally, here is a more involved example. This module defines a plugin that adds a button to the DrRacket frame that, when clicked, reverses the contents of the definitions window. It also adds an easter egg. Whenever the definitions text is modified, it checks to see if the definitions text contains the text “egg”. If so, it adds “easter ” just before.

#lang racket/base

(require drracket/tool

racket/class

racket/gui/base

racket/unit

mrlib/switchable-button)

(provide tool@)

(define secret-key "egg")

(define to-insert "easter ")

(define tool@

(unit

(import drracket:tool^)

(export drracket:tool-exports^)

(define easter-egg-mixin

(mixin ((class->interface text%)) ()

(inherit begin-edit-sequence

end-edit-sequence

insert

get-text)

(define/augment (on-insert start len)

(begin-edit-sequence))

(define/augment (after-insert start len)

(check-range (max 0 (- start (string-length secret-key)))

(+ start len))

(end-edit-sequence))

(define/augment (on-delete start len)

(begin-edit-sequence))

(define/augment (after-delete start len)

(check-range (max 0 (- start (string-length secret-key)))

start)

(end-edit-sequence))

(define/private (check-range start stop)

(let/ec k

(for ((x (in-range start stop)))

(define after-x

(get-text x (+ x (string-length secret-key))))

(when (string=? after-x secret-key)

(define before-x

(get-text (max 0 (- x (string-length to-insert))) x))

(unless (string=? before-x to-insert)

(insert to-insert x x)

(k (void)))))))

(super-new)))

(define reverse-button-mixin

(mixin (drracket:unit:frame<%>) ()

(super-new)

(inherit get-button-panel

get-definitions-text)

(inherit register-toolbar-button)

(let ((btn

(new switchable-button%

(label "Reverse Definitions")

(callback (λ (button)

(reverse-content

(get-definitions-text))))

(parent (get-button-panel))

(bitmap reverse-content-bitmap))))

(register-toolbar-button btn #:number 11)

(send (get-button-panel) change-children

(λ (l)

(cons btn (remq btn l)))))))

(define reverse-content-bitmap

(let* ((bmp (make-bitmap 16 16))

(bdc (make-object bitmap-dc% bmp)))

(send bdc erase)

(send bdc set-smoothing 'smoothed)

(send bdc set-pen "black" 1 'transparent)

(send bdc set-brush "blue" 'solid)

(send bdc draw-ellipse 2 2 8 8)

(send bdc set-brush "red" 'solid)

(send bdc draw-ellipse 6 6 8 8)

(send bdc set-bitmap #f)

bmp))

(define (reverse-content text)

(for ((x (in-range 1 (send text last-position))))

(send text split-snip x))

(define snips

(let loop ((snip (send text find-first-snip)))

(if snip

(cons snip (loop (send snip next)))

'())))

(define released-snips

(for/list ((snip (in-list snips))

#:when (send snip release-from-owner))

snip))

(for ((x (in-list released-snips)))

(send text insert x 0 0)))

(define (phase1) (void))

(define (phase2) (void))

(drracket:get/extend:extend-definitions-text easter-egg-mixin)

(drracket:get/extend:extend-unit-frame reverse-button-mixin)))