| CONTINUE from function within loop [message #86478] |
Tue, 12 November 2013 21:19  |
spluque
Messages: 33
Registered: September 2013
|
Member |
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Hi,
I read the CATCH and ON_ERROR help pages, but I can't see how to handle the following situation. Say we have a FOR loop where a function is called for each iteration:
FOR i=0, 10 DO BEGIN
print, myfun(i)
ENDFOR
I would like MYFUN to continue with the next iteration if it runs into an error. Naively, this should show what I'm looking for:
FUNCTION MYFUN, X
[BODY]
IF [condition] THEN BEGIN
message, 'A problem with X', /informational
CONTINUE
ENDIF
[REST IF OK]
RETURN, [something]
END
But, of course, CONTINUE only works within an FOR/ENDFOR block, not this way. How does one accomplish this?
Thanks,
Seb
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| Re: CONTINUE from function within loop [message #86479 is a reply to message #86478] |
Tue, 12 November 2013 21:40  |
Craig Markwardt
Messages: 1869
Registered: November 1996
|
Senior Member |
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On Wednesday, November 13, 2013 12:19:43 AM UTC-5, Sebastian Luque wrote:
> Hi,
>
>
>
> I read the CATCH and ON_ERROR help pages, but I can't see how to handle the following situation. Say we have a FOR loop where a function is called for each iteration:
>
>
>
> FOR i=0, 10 DO BEGIN
>
> print, myfun(i)
>
> ENDFOR
>
>
>
> I would like MYFUN to continue with the next iteration if it runs into an error. Naively, this should show what I'm looking for:
>
>
>
> FUNCTION MYFUN, X
> [BODY]
> IF [condition] THEN BEGIN
> message, 'A problem with X', /informational
> CONTINUE
> ENDIF
> [REST IF OK]
> RETURN, [something]
> END
>
> But, of course, CONTINUE only works within an FOR/ENDFOR block, not this way. How does one accomplish this?
You're right, because CONTINUE only works within the same lexical scope.
You could do this by putting a CATCH within your main loop, which will catch your MESSAGE within MYFUN. That's a little dangerous because it will catch *every* error though.
A better practice is to return a separate status variable MYFUN indicating success or failure, and have the main loop check the variable and decide what to do.
Something like this...
function myfun, x, status=status
status = -1
;; Failure case
if [condition] then return, !values,d_nan
[ rest of MYFUN ]
;; Success case
status = 1
return, [something]
end
for i = 0, 10 do begin
y = myfun(x, status=status)
if status LT 0 then continue
print, y
endfor
Craig
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| Re: CONTINUE from function within loop [message #86480 is a reply to message #86478] |
Tue, 12 November 2013 22:32 |
Moritz Fischer
Messages: 32
Registered: June 2013
|
Member |
|
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Hi,
If this was possible, it would make your myfun routine very hard to reuse.
Why don't you add a keyword to MYFUN ?
Replace the loop by
%<---------------------
FOR i=0, 10 DO BEGIN
tmp = myfun(i, FAILED=FAILED, MSG=MSG)
IF FAILED THEN BEGIN
message, MSG, /INFO
CONTINUE
ENDIF ELSE print, tmp
ENDFOR
%<---------------------
where
%<---------------------
FUNCTION MYFUN, X, FAILED = FAILED, MSG=MSG
[BODY]
FAILED = [condition]
IF FAILED THEN BEGIN
MSG = 'A problem with X',
RETURN, !NULL
ENDIF
[REST IF OK]
RETURN, [something]
END
%<---------------------
But this does not work if MYFUN actually runs into an error ( but only
if [condition] is true ) .
What's wrong with putting thte following into the FOR loop?
%<---------------------
CATCH, err
IF err NE 0 THEN BEGIN
message, !error_state.message, /INFO
CATCH, /cancel
CONTINUE
ELSE print, myfun(i)
%<---------------------
I think (hope) this is the only way you can jump to another level.
cheers
Am 13.11.2013 06:19, schrieb Sebastian Luque:
> Hi,
>
> I read the CATCH and ON_ERROR help pages, but I can't see how to
> handle the following situation. Say we have a FOR loop where a
> function is called for each iteration:
>
> FOR i=0, 10 DO BEGIN print, myfun(i) ENDFOR
>
> I would like MYFUN to continue with the next iteration if it runs
> into an error. Naively, this should show what I'm looking for:
>
> FUNCTION MYFUN, X
>
> [BODY]
>
> IF [condition] THEN BEGIN message, 'A problem with X',
> /informational CONTINUE ENDIF
>
> [REST IF OK]
>
> RETURN, [something]
>
> END
>
> But, of course, CONTINUE only works within an FOR/ENDFOR block, not
> this way. How does one accomplish this?
>
> Thanks, Seb
>
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| Re: CONTINUE from function within loop [message #86484 is a reply to message #86479] |
Wed, 13 November 2013 07:21 |
spluque
Messages: 33
Registered: September 2013
|
Member |
|
|
On Tuesday, November 12, 2013 11:40:34 PM UTC-6, Craig Markwardt wrote:
> On Wednesday, November 13, 2013 12:19:43 AM UTC-5, Sebastian Luque wrote:
>
>> Hi,
>
>>
>
>>
>
>>
>
>> I read the CATCH and ON_ERROR help pages, but I can't see how to handle the following situation. Say we have a FOR loop where a function is called for each iteration:
>
>>
>
>>
>
>>
>
>> FOR i=0, 10 DO BEGIN
>
>>
>
>> print, myfun(i)
>
>>
>
>> ENDFOR
>
>>
>
>>
>
>>
>
>> I would like MYFUN to continue with the next iteration if it runs into an error. Naively, this should show what I'm looking for:
>
>>
>
>>
>
>>
>
>> FUNCTION MYFUN, X
>
>> [BODY]
>
>> IF [condition] THEN BEGIN
>
>> message, 'A problem with X', /informational
>
>> CONTINUE
>
>> ENDIF
>
>> [REST IF OK]
>
>> RETURN, [something]
>
>> END
>
>>
>
>> But, of course, CONTINUE only works within an FOR/ENDFOR block, not this way. How does one accomplish this?
>
>
>
> You're right, because CONTINUE only works within the same lexical scope.
>
>
>
> You could do this by putting a CATCH within your main loop, which will catch your MESSAGE within MYFUN. That's a little dangerous because it will catch *every* error though.
>
>
>
> A better practice is to return a separate status variable MYFUN indicating success or failure, and have the main loop check the variable and decide what to do.
>
>
>
> Something like this...
>
> function myfun, x, status=status
>
> status = -1
>
> ;; Failure case
>
> if [condition] then return, !values,d_nan
>
> [ rest of MYFUN ]
>
> ;; Success case
>
> status = 1
>
> return, [something]
>
> end
>
>
>
> for i = 0, 10 do begin
>
> y = myfun(x, status=status)
>
> if status LT 0 then continue
>
> print, y
>
> endfor
>
This is a very clean solution!
Thanks,
Seb
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