According to [1] this is the expected behavior. There is stated that
"When a “rest argument” is declared after optional arguments, arguments
in an application are first consumed by the optional-argument positions,
so the rest argument is non-empty only when more arguments
are provided that the total number of required and optional
arguments."
Unfortunately this or a similar explanation is missing in the manual. Maybe
it should be mentioned there.
Regards,
Tobias
[1] Keyword and Optional Arguments in PLT Scheme, Flatt; Barzilay
On Wed, 26 Sep 2012 22:46:20 +0200, Norman Gray <[email protected]>
wrote:
Greetings
The behaviour of call-with-semaphore doesn't appear to match the
documentation, or else I'm misunderstanding the documentation.
Consider:
(define (printit m)
(printf "msg begin:~a~%" m))
(define try
(let ((sema (make-semaphore 1)))
(λ (msg)
(call-with-semaphore sema
printit
;#f
msg))))
(try "second")
With #f commented out, I get (with Racket 5.3):
call-with-semaphore: procedure arity does not match extra-argument count
procedure: #<procedure:printit>
extra-argument count: 0
With #f uncommented, it works as expected:
Welcome to DrRacket, version 5.3 [3m].
Language: racket; memory limit: 128 MB.
msg begin:second
The documentation says:
(call-with-semaphore sema
proc
[ try-fail-thunk]
arg ...) → any
However it appears that the try-fail-chunk argument is not in fact
optional.
----
Separately, it appears that CALL-WITH-SEMAPHORE returns the value that
(proc args…) returns. However the documentation doesn't actually say
that. Is that just an oversight, or is the return value of
CALL-WITH-SEMAPHORE undefined?
Best wishes,
Norman
--
---------------------------------------------------------
Tobias Hammer
DLR / Institute of Robotics and Mechatronics
Muenchner Str. 20, D-82234 Wessling
Tel.: 08153/28-1487
Mail: [email protected]
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