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better code order

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svn: r13168
This commit is contained in:
Eli Barzilay 2009-01-16 16:29:53 +00:00
parent 9e305c79e3
commit c5f8c43dbf
1 changed files with 18 additions and 18 deletions
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36
collects/scheme/promise.ss
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@ -59,10 +59,24 @@
;; X = (force (lazy X)) = (force (lazy (lazy X))) = (force (lazy^n X))
(define-syntax (lazy stx)
(syntax-case stx ()
[(lazy expr) (with-syntax ([proc (syntax-property
(syntax/loc stx (lambda () expr))
'inferred-name (syntax-local-name))])
(syntax/loc stx (make-promise proc)))]))
[(lazy expr)
(with-syntax ([proc (syntax-property (syntax/loc stx (lambda () expr))
'inferred-name (syntax-local-name))])
(syntax/loc stx (make-promise proc)))]))
;; Creates a promise that does not compose
;; X = (force (delay X)) = (force (lazy (delay X)))
;; = (force (lazy^n (delay X)))
;; X = (force (force (delay (delay X)))) != (force (delay (delay X)))
;; so each sequence of `(lazy^n o delay)^m' requires m `force's and a
;; sequence of `(lazy^n o delay)^m o lazy^k' requires m+1 `force's (for k>0)
;; (This is not needed with a lazy language (see the above URL for details),
;; but provided for regular delay/force uses.)
(define-syntax (delay stx)
(syntax-case stx ()
[(delay expr)
(syntax/loc stx
(lazy (make-promise (call-with-values (lambda () expr) list))))]))
;; For simplicity and efficiency this code uses thunks in promise values for
;; exceptions: this way, we don't need to tag exception values in some special
@ -80,20 +94,6 @@
(error 'force "reentrant promise ~v" name)
(error 'force "reentrant promise")))))
;; Creates a promise that does not compose
;; X = (force (delay X)) = (force (lazy (delay X)))
;; = (force (lazy^n (delay X)))
;; X = (force (force (delay (delay X)))) != (force (delay (delay X)))
;; so each sequence of `(lazy^n o delay)^m' requires m `force's and a
;; sequence of `(lazy^n o delay)^m o lazy^k' requires m+1 `force's (for k>0)
;; (This is not needed with a lazy language (see the above URL for details),
;; but provided for regular delay/force uses.)
(define-syntax (delay stx)
(syntax-case stx ()
[(delay expr)
(syntax/loc stx
(lazy (make-promise (call-with-values (lambda () expr) list))))]))
;; force iterates on lazy promises (forbids dependency cycles)
;; * (force X) = X for non promises
;; * does not deal with multiple values, except for `delay' promises at the