Thanks, that's clear now.
Another question regarding events: Why is it forbidden to put a handle-evt
inside another handle- or wrap-evt?
I couldn't come up with a situation where this could cause trouble.
Especially as it is allowed to nest handle-evts if i put a guard-evt or a
struct with prop:evt in between.
Tobias
On Thu, 28 Mar 2013 16:17:00 +0100, Matthew Flatt <[email protected]>
wrote:
Sometimes, `sync' picks the first evt that it is given before even
trying the second evt enough to call the evt-generating function. That
is, `sync' looks far enough to see all arguments are `evt?', but
calling the evt-generator part of a guard evt is part of the attempt to
choose the specific guard evt, and that action doesn't happen if some
other evt succeeds first.
I'll work on the docs to clarify.
Yes, `proc' should be `generator'. But, `generator' also should be
changed, because "generator" now means something specific and
different.
At Thu, 28 Mar 2013 16:08:09 +0100, Tobias Hammer wrote:
Hi,
i am trying to understand how nack-guard-evt works. Therefore i created
the appended test program. Sometimes it stops with the error message and
sometimes it prints the three values. It is clear to me what the error
means and why it is raised.
What i am not understanding is, why the nack generator is not run every
time sync is called. I would have expected from the docs that it is run
on
every sync.
Can someone clarify why my assumptions are wrong and how nack-guard-evt
is
expected to behave?
Related question: The docs for the function talk abound 'proc', should
it
be 'generator'?
Tobias
;; -----------------------------
#lang racket
(define nack #f)
(sync (handle-evt
always-evt
(lambda (_) 'ALWAYS))
(nack-guard-evt
(lambda (e)
(set! nack e)
never-evt)))
nack
(printf "~a\n" (sync/timeout 0. nack))
> 'ALWAYS
#f
. . sync/timeout: contract violation
expected: evt?
given: #f
argument position: 2nd
other arguments...:
0.0
OR
> 'ALWAYS
#<evt>
#<void>
--
---------------------------------------------------------
Tobias Hammer
DLR / Robotics and Mechatronics Center (RMC)
Muenchner Str. 20, D-82234 Wessling
Tel.: 08153/28-1487
Mail: [email protected]
____________________
Racket Users list:
http://lists.racket-lang.org/users
--
---------------------------------------------------------
Tobias Hammer
DLR / Robotics and Mechatronics Center (RMC)
Muenchner Str. 20, D-82234 Wessling
Tel.: 08153/28-1487
Mail: [email protected]
____________________
Racket Users list:
http://lists.racket-lang.org/users
