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Remove the special case hack for getting zero values at the end of a

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generator.  This will make this:

  (generator (yield 1) (yield))

also repeat #<void> when it's done which will be very confusing.  Better
just add a note in the docs on (generator (yield 1)) returning no values
when it's done.

Also, remove some of the `case-lambda' optimizations...

svn: r17983
This commit is contained in:
Eli Barzilay 2010-02-05 03:22:12 +00:00
parent 3a08648dab
commit d5822a3ee5
1 changed files with 7 additions and 19 deletions
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26
collects/scheme/generator.ss
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@ -54,31 +54,19 @@
(define-syntax-rule (generator body0 body ...)
(let ([state 'fresh])
(define (cont)
(define yielder
;; this `case-lambda' is ... um ... for "speed"...
(case-lambda
[() (set! state 'suspended)
(shift-at yield-tag k (set! cont k) (values))]
[(v) (set! state 'suspended)
(shift-at yield-tag k (set! cont k) v)]
[vs (set! state 'suspended)
(shift-at yield-tag k (set! cont k) (apply values vs))]))
(define (yielder . vs)
(set! state 'suspended)
(shift-at yield-tag k (set! cont k) (apply values vs)))
(set! state 'running)
(reset-at yield-tag
(parameterize ([current-yielder yielder])
(call-with-values
(lambda () (begin body0 body ...))
;; get here only on at the end of the generator
(case-lambda
;; Note: in the first case, the generator was invoked with no
;; arguments, so returning no values is more symmetric. But
;; this is a common case, and probably people would expect a
;; void result more than no values.
[() (set! cont void)]
[(r) (set! cont (lambda () r))]
[rs (set! cont (lambda () (apply values rs)))]))
(set! state 'done)
(cont))))
(lambda rs
(set! state 'done)
(set! cont (lambda () (apply values rs)))
(cont))))))
(define (err [what "send a value to"])
(error 'generator "cannot ~a a ~a generator" what state))
(define generator