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Update NEWS with details on guard and autoloads.

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* NEWS: Update.
This commit is contained in:
Andy Wingo 2020-01-10 22:09:17 +01:00
parent 8068994ba8
commit 640eb5d1b3
1 changed files with 46 additions and 17 deletions
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63
NEWS
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@ -7,13 +7,54 @@ Please send Guile bug reports to bug-guile@gnu.org.
Changes since alpha 2.9.8: Changes since alpha 2.9.8:
** Fix performance of SRFI-43 vector-fill! * Notable changes
** `define-module' #:autoload no longer pulls in the whole module
One of the ways that a module can use another is "autoloads". For
example:
(define-module (a) #:autoload (b) (make-b))
In this example, module `(b)' will only be imported when the `make-b'
identifier is referenced. However besides the imprecision about when a
given binding is actually referenced, this mechanism used to cause the
whole imported module to become available, not just the specified
bindings. This has now been changed to only import the specified bindings.
This is a backward-incompatible change. The fix is to mention all
bindings of interest in the autoload clause. Feedback is welcome.
** `guard' no longer unwinds the stack for clause tests
SRFI-34, and then R6RS and R7RS, defines a `guard' form that is a
shorthand for `with-exception-handler'. The cond-like clauses for the
exception handling are specified to run with the continuation of the
`guard', while any re-propagation of the exception happens with the
continuation of the original `raise'.
In practice, this means that one needs full `call-with-continuation' to
implement the specified semantics, to be able to unwind the stack to the
cond clauses, then rewind if none match. This is not only quite
expensive, it is also error-prone as one usually doesn't want to rewind
dynamic-wind guards in an exceptional situation. Additionally, as
continuations bind tightly to the current thread, it makes it impossible
to migrate a subcomputation with a different thread if a `guard' is live
on the stack, as is done in Fibers.
Guile now works around these issues by running the test portion of the
guard expressions within the original `raise' continuation, and only
unwinding once a test matches. This is an incompatible semantic change
but we think the situation is globally much better, and we expect that
very few people will be affected by the change.
** Improve SRFI-43 vector-fill!
SRFI-43 vector-fill! now has the same performance whether an optional SRFI-43 vector-fill! now has the same performance whether an optional
range is provided or not, and is also provided in core. As a side range is provided or not, and is also provided in core. As a side
effect, vector-fill! and vector_fill_x no longer work on non-vector effect, vector-fill! and vector_fill_x no longer work on non-vector
rank-1 arrays. Such cases were handled incorrectly before; for example, rank-1 arrays. Such cases were handled incorrectly before; for example,
prior to this change, prior to this change:
(define a (make-vector 10 'x)) (define a (make-vector 10 'x))
(define b (make-shared-array a (lambda (i) (list (* 2 i))) 5)) (define b (make-shared-array a (lambda (i) (list (* 2 i))) 5))
@ -21,21 +62,9 @@ prior to this change,
=> #1(y y y x x) => #1(y y y x x)
This is now an error. Instead, use array-fill! (or array_fill_x). This is now an error. Instead, use array-fill!.
**
Changes in alpha 2.9.8 (since alpha 2.9.7):
* Bug fixes
** Fix bug in which abort_to_prompt used an invalid stack pointer
This bug manifested itself as a bootstrap compile error on some systems,
notably Ubuntu 18.04 on x86-64, and was due to failing to recalculate a
local variable after a possible stack relocation.
** SRFI-35 does a #:re-export-and-replace on `&error'
** SRFI-35 avoids compiler warnings for multiply-defined condition types
Changes in alpha 2.9.x (since the stable 2.2 series): Changes in alpha 2.9.x (since the stable 2.2 series):