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179 lines
4.0 KiB
HTML
179 lines
4.0 KiB
HTML
27 years ago
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<title>Release Notes for DrScheme</title>
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<body>
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<h2><img align=center
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src="http://www.cs.rice.edu/CS/PLT/packages/drscheme/logo.gif"
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alt="[DrScheme logo]">
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DrScheme Release Notes</h2>
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<p>
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<b>Current Release</b>: 0.41.<br>
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<b>Release Date</b>: April 16, 1996.
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<p>
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The following is a list of differences between this release and the
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previous one.
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<h3>Highlights</h3>
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A mail alias has been created for reporting bugs.
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Bug reports for DrScheme (and other PLT software) should be sent to:
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<pre> plt-bugs@cs.rice.edu
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</pre>
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<p>
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The error messages in DrScheme have been improved and should now
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be more descriptive of the problem.
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<p>
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Several changes to the MzScheme language affecting the class system,
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exceptions and macros have been made in release 0.41.
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Many of the new features are incompatible with the old system.
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<h4>Classes</h4>
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`make-class' and `make-class*' have been replaced with `class'
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and `class*'.
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`class' looks a lot like `make-class', but there are
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some important differences:
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<ol>
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<li>
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The initialization procedure of `make-class' is gone.
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Instead, in `class', there is always an implicit `lambda'
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(really something like an `opt-lambda'). As a result,
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the arguments to `make-object' can be used in the ivar
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initialization expressions.
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<li>
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All ivars are intialized in order, even across clauses.
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<li>
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A new kind of clause is available: `sequence' clauses
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evaluate expressions without assigning them to ivars.
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<li>
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The scope of `super-init' includes all of the clauses now.
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(It used to be only the initialization procedure.)
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<li>
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apply-super-init is gone. Use (apply super-init ...) instead.
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</ol>
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<p>
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For example, this expression:
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<pre> (make-class c%
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(private y)
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(public [x (lambda () y)])
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(lambda (v)
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(set! y v)
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(super-init)))
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</pre>
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can now be written:
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<pre> (class c% (v) ; (v) is the arg list for the implicit lambda
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(private [y v])
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(public [x (lambda () y)])
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(sequence
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(super-init)))
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</pre>
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or even better:
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<pre> (class c% (y)
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(public [x (lambda () y)])
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(sequence
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(super-init)))
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</pre>
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This expression:
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<pre> (make-class d%
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(public [x 5]))
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</pre>
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translates to:
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<pre> (class d% args
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(public [x 5])
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(sequence
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(apply super-init args)))
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</pre>
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Since this happens a lot, mzlib's `macros.ss' defines `class-asi'
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(auto super init):
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<pre> (class-asi d%
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(public [x 5]))
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</pre>
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(Here, `make-class' was simply changed to `class-asi'.)
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<p>
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Default expressions can be provided for `make-object' arguments
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(`opt-lambda' style):
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<pre> (class x% (a [b (add1 a)] [c (lambda (x) b)])
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...)
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</pre>
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Each default value expression is not evaluated when an argument is
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supplied. The scope of all argument variables includes all default
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value expressions (i.e., like `letrec', while `opt-lambda' is like
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`let*').
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<h4>Exceptions</h4>
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Errors are now always signaled using exceptions. The `raise' procedure
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takes any value and invokes the current exception handler with that
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value. All primitive errors invoke `raise' with an instance of the
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struct type `exn'. There is always a current exception handler, just
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as there has previously been a current error handler in MzScheme.
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(The current error display and escape handlers are still used by the
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default eception handler). A `with-handlers' form provides ML-like
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syntax for handling exceptions in a subexpression.
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<h4>Macros</h4>
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`defmacro' and `letmacro' have been replaced with `define-macro' and
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`let-macro'. The only difference is that the implicit `lambda' must
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now be explicit:
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(defmacro when (test . body)
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`(if ,test
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(begin
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,@body)))
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becomes
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(define-macro when
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(lambda (test . body)
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`(if ,test
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(begin
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,@body))))
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mzlib's `compat.ss' defines macros for `defmacro' and `letmacro'.
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<h4>Package Macro</h4>
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The `package' macro in mzlib's "macros.ss" has been renamed to
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`define-some' to avoid confusion with DrScheme's `make-package' form.
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<h4>Error Messages</h4>
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The error messages from MzScheme have been revised.
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Hopefully, the syntax error messages will now be more helpful.
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</body>
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