2 Implementing DrRacket Plugins🔗

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.

When DrRacket starts up, it looks for tools by reading fields in the info.rkt file of each collection and the newest version of each PLaneT package installed on the system. (Technically, DrRacket looks in a cache of the "info.rkt" files contents created by raco setup. Be sure to re-run raco setup if you change the contents of the info.rkt files). DrRacket checks for these fields:

The drracket-tools field names a list of tools in this collection. Each tool is specified as a collection path, relative to the collection where the info.rkt file resides. As an example, if there is only one tool named tool.rkt, this suffices:

(define drracket-tools (list (list "tool.rkt")))

If the drracket-tool-icons or drracket-tool-names fields are present, they must be the same length as drracket-tools. The drracket-tool-icons field specifies the path to an icon for each tool and the name of each tool. If it is #f, no tool is shown. If it is a relative pathname, it must refer to a bitmap and if it is a list of strings, it is treated the same as the arguments to lib, inside require.

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.

For example, if the info.rkt file in a collection contains:
#lang info
(define drracket-tool-names (list "Tool Name"))
(define drracket-tools (list (list "tool.rkt")))
then the same collection would be expected to contain a tool.rkt file. It might contain something like this:
#lang racket/gui
(require drracket/tool)
(provide tool@)
(define tool@
    (import drracket:tool^)
    (export drracket:tool-exports^)
    (define (phase1) (message-box "tool example" "phase1"))
    (define (phase2) (message-box "tool example" "phase2"))
    (message-box "tool example" "unit invoked")))
This tool just opens a few windows to indicate that it has been loaded and that the phase1 and phase2 functions have been called.

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
(provide tool@)
(define secret-key "egg")
(define to-insert "easter ")
(define tool@
    (import drracket:tool^)
    (export drracket:tool-exports^)
    (define easter-egg-mixin
      (mixin ((class->interface text%)) ()
        (inherit begin-edit-sequence
        (define/augment (on-insert start len)
        (define/augment (after-insert start len)
          (check-range (max 0 (- start (string-length secret-key)))
                       (+ start len))
        (define/augment (on-delete start len)
        (define/augment (after-delete start len)
          (check-range (max 0 (- start (string-length secret-key)))
        (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)))))))
    (define reverse-button-mixin
      (mixin (drracket:unit:frame<%>) ()
        (inherit get-button-panel
        (inherit register-toolbar-button)
        (let ((btn
               (new switchable-button%
                    (label "Reverse Definitions")
                    (callback (λ (button)
                    (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)
    (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))
      (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)))