▼Plugins: Extending Dr Racket
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1 Implementing DrRacket Tools

Tools 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, to add buttons to the DrRacket frame or to add additional languages to DrRacket) 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 tool.rkt library in the drscheme collection. The drracket:tool^ signature contains all of the names listed in this manual. The unit must export the drracket:tool-exports^ signature.

The drracket:tool-exports^ signature contains two names: phase1 and phase2. These names must be bound to thunks. After all of the tools are loaded, all of the phase1 functions are called and then all of the phase2 functions are called. Certain primitives can only be called during the dynamic extent of those calls.

This mechanism is designed to support DrRacket’s drracket:language:language<%> extension capabilities. That is, this mechanism enables two tools to cooperate via new capabilities of languages. The first phase is used for adding functionality that each language must support and the second is used for creating instances of languages. As an example, a tool may require certain specialized language-specific information. It uses phase1 to extend the drracket:language:language<%> interface and supply a default implementation of the interface extension. Then, other languages that are aware of the extension can supply non-default implementations of the additional functionality.

Phase 1 functions:

Phase 2 functions:

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 setup/infotab
  (define drracket-name "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 scheme/gui
  (require drracket/tool)
  
  (provide tool@)
  
  (define tool@
    (unit
      (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.

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