Tools are designed for major extensions in DrScheme's functionality. To extend the appearance or the functionality the DrScheme window (say, to annotate programs in certain ways, to add buttons to the DrScheme frame or to add additional languages to DrScheme) use a tool. The Static Debugger, the Syntax Checker, the Stepper, and the teaching languages are all implemented as tools.
Libraries are for extensions of DrScheme that only want to add new functions and other values bound in the users namespace. See the DrScheme manual for more information on constructing libraries.
Tools rely heavily on MzScheme's units. See units for information on how to construct units. They also require understanding of libraries and collections.
When DrScheme starts up, it looks for tools by reading fields in the info.ss file of each top-level collection. DrScheme checks for these fields:
(listof (listof string[subcollection-name]))
(listof (union #f string))
(listof (union #f (
consstring[filename] (listof string[collection-name]))))
(listof (union #f string[url]))
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.ss file
resides. As an example, if there is only one tool named
tool.ss, this sufficies:
(define tools (
are present, they must be the same length as
tool. They specify the path to an icon for each tool
and the name of each tool. This information shows up in the
about box, Help Desk's bug report form, and the icon appears
on the splash screen as the tool is loaded at DrScheme's
tools files must contain a module that
tool@, which must be bound to a
unit/sig The unit
must import the
drscheme:tool^ signature, which is
provided by the tool.ss library in the
drscheme collection. The
signature contains all of the names listed in this manual.
The unit must export the
drscheme:tool-exports^ signature contains two
phase2. These names must
be bound to thunks. After all of the tools are loaded, all of
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 DrScheme's
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
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
Phase 1 functions:
Phase 2 functions:
If the tools raises an error as it is loaded, invoked, or as
phase2 thunks are called,
DrScheme catches the error and displays a message box. Then,
DrScheme continues to start up, without the tool.
For example, if the info.ss file in a collection contains:
(module info (lib "infotab.ss" "setup") (define name "Tool Name") (define tools (
then the same collection would be expected to contain a tool.ss file. It might contain something like this:
mzscheme(require (lib "tool.ss" "drscheme") (lib "mred.ss" "mred") (lib "unitsig.ss")) (provide tool@) (define tool@ (unit/sig drscheme:tool-exports^ (import drscheme:tool^) (define (phase1) (message-box "tool example" "phase1")) (define (phase2) (message-box "tool example" "phase2")))))
This tool just opens a window to indicate that it has been loaded.
If a language can be implemented as a module (see module for details) and the standard language settings are sufficient, simply create an info.ss file in the collection where the module is saved. Include these definitions:
#f. Clicking the corresponding language's name in the interactions window opens a web browser to the url.
require, except not plain strings). Each specification must be a module that exports a function named
. Each of these
functions must match MzScheme's
primitive's contract, but may read different concrete syntax.
The lists must have the same length.
As an example, the Essentials of Programming Languages language specification's info.ss looks like this:
(module info (lib "infotab.ss" "setup") (define name "EoPL Support") (define drscheme-language-modules (list '("eopl-lang.ss" "eopl"))) (define drscheme-language-positions (list '("Essentials of Programming Languages"))))
This info.ss file indicates that there is a single language in this collection. The module that implements the language is the eopl-lang.ss file in the eopl collection. Additionally, the langauge dialog will contain Essentials of Programming Languages as a potential language.
For collections that define multiple (related) languages, if the language-positions contain multiple strings, the languages whose leading strings match are grouped together. That is, if two languages have strings:
'("My Text" "First Language")
'("My Text" "Second Language")
the two languages will be grouped together in the language dialog.
With some additional work, any language that can be compiled
to MzScheme's language is supported by the tools interface,
not just those that use standard configurations and
Each language is a class that implement the
drscheme:language:language<%> interface. DrScheme also
provides two simpler interfaces:
that build implementations of
language^s from these simpler interfaces.
Once you have an implementation of the
drscheme:language:language<%> interface, call
drscheme:language-configuration:add-language to add the language
Each language comes with its own type, called
settings. This can be any type the language
designer chooses, but to aid documentation, we call it
settings here. The settings type is expected to
contain parameters of the language, such as case
sensitivity, etc. The implementor of the language provides a
GUI so the user can configure the settings and all of the
language's operations accept a setting. DrScheme maintains
the current settings for each language.
Some tools may require additional functionality from the
drscheme:language:language<%> interface. The
function and the
mixin make this possible.
For example, the MrFlow tool expands programs, analyzes it
and then displays sets of values for each program point.
These sets of values should be rendered in the syntax of the
language that MrFlow analyzes. Since MrFlow doesn't apriori
know which languages are available, it can call
to extend the
interface with a method for rendering sets of values and
provide a default implementation of that method. Tools that
know about MrFlow can then override the value rendering
method to provide a language-specific implementation of
value rendering. Additionally, since the
adds the default implementation for the value-set rendering
method, all languages at least have some form of value-set
Each frame in DrScheme has certain menus and functionality,
most of which is achieved by using the framework.
Additionally, there is one mixin that DrScheme provides to
augment that. It is
Be sure to mix it into any new frame class that you add to
Each of the names:
is bound to an extender function. In order to change the behavior of drscheme, you can derive new classes from the standard classes for the frame, texts, canvases. Each extender accepts a function as input. The function it accepts must take a class as it's argument and return a classes derived from that class as its result. For example:
(drscheme:get/extend:extend-interactions-text (lambda (super%) (class super% (public method1) (define (method1 x) ...) ...)))
extends the interactions text class with a method named
Macro-expanding a program may involve arbitrary computation
and requires the setup of the correct language. To aid this,
DrScheme's tool interface provides
drscheme:eval:expand-program to help. Use
this method to extract the fully expanded program text in a
Because expanding the user's program may require DrScheme to
evaluate arbitrary code that the user wrote, tools that
expand the user's program should also allow the user to break
the expansion. To help with this, the tools interfaces
provides these methods:
Since your tool will be expanding the program text, you
should be both overriding
to disable your tool and calling them
to ensure that only one expansion is happening
at a time.
Finally, DrScheme provides the
method. This method controls what behavior the Break button
DrScheme provides support for multiple editor modes. Tools
register modes via
drscheme:modes:add-mode. Each mode is
visible in the Modes submenu of the Edit
menu. Initially, DrScheme only supports two modes: scheme
mode and text mode.
DrScheme automatically selects a mode for each open file based on the file's extension. If the file ends with .txt, DrScheme uses text mode. Otherwise, DrScheme uses Scheme mode.