diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 62 |
1 files changed, 29 insertions, 33 deletions
@@ -27568,14 +27568,17 @@ as the closure body terminates. .coNP Function @ sys:capture-cont .synb -.mets (sys:capture-cont < name <> [ context-form ]) +.mets (sys:capture-cont < name < receive-fun <> [ context-form ]) .syne .desc The .code sys:capture-cont function captures a continuation, and also serves as the resume point for the resulting continuation. Which of these two situations is the -case (capture or resumption) is distinguished by the return value. +case (capture or resumption) is distinguished by the use of the +.meta receive-fun +argument, which must be a function capable of being called with one +argument. A block named .meta name @@ -27594,33 +27597,29 @@ uses its own name. The .code sys:capture-cont -function returns a cons cell. The -.code car -field of the cell distinguishes the capture and resume situations. -If the -.code car -is the object -.codn t , -then it indicates capture, and in this case, the -.code cdr -field contains the continuation function. When the continuation -function is called, the +function captures a continuation, represented as a function. +It immediately calls +.metn receive-fun , +passing it it the continuation function as an argument. +If +.meta receive-fun +returns normally, then .code sys:capture-cont -function appears to return again. This time the -.code car -of the returned cell is -.code nil -indicating that the -.code cdr -field holds the argument value which was passed to the continuation -function. +returns whatever value +.meta receive-fun +returns. -The invoked continuation function will terminate when the resumed context -terminates. If that context terminates normally (by returning from the -delimiting block named by -.metn name ), -then the result value of that block will appear as the return value -of the continuation function. +When the continuation function is called (thereby resuming the captured +continuation), inside that resumed continuation, +.code sys:capture-cont +function appears to return. Its return value is the argument +which was passed to the continuation function. The continuation function +appears suspended while the resumed continuation executes. +If the resumed continuation context terminates normally (by terminating +the continuation's delimiting block named by +.metn name ) +the continuation function terminates, and yields the value which emerged +from the terminated block. If the symbol .code sys:cont-poison @@ -27661,12 +27660,9 @@ operator. .cblk (defmacro suspend (:form form name var . body) - (with-gensyms (cap val) - ^(tree-bind (,cap . ,val) (sys:capture-cont ',name ',form) - (if ,cap - (let ((,var ,val)) - (sys:abscond-from ,name ,*body)) - ,val)))) + ^(sys:capture-cont ',name (lambda (,var) + (sys:abscond-from ,name ,*body)) + ',form)) .cble .coNP Operator @ sys:abscond-from |