I managed to find another way to crash J. I'm not sure whether the fault
lies in J itself or in Qt, but... here's the story:
When J is running on something that takes a long time (for example,
fetching hundreds of files, each fetched file requiring its own shell
command), it would be nice to let the user know that J is doing what it is
supposed to. Users know that computers sometimes have problems, and they
like having a mechanism to distinguish between failure and functioning
modes of operation. And while jconsole has a nice mechanism for this
(smoutput), jqt does not share this behavior.
So, I thought, let's introduce a small delay between statements, so that
the display can update and the user can see something happening.
Thus:
Progressively=:1 :0
0 u Progressively y
:
wd 'timer 0'
smoutput u x{y
next=.x+1
if. next<#y do.
sys_timer_z_=: next u Progressively y"_
wd 'timer 1'
end.
)
But when I go to try it out, I got a syntax error while trying to update
sys_timer_z_ when it is on the stack. (Shouldn't that be a stack error, if
it needs to be an error at all?)
And when I tried to reproduce that syntax error with debugging enabled, so
I could see what was going on, I crashed J.
Here's my test case:
*: Progressively 2 3 5 7 11
My suspicion is that I've violated some assumptions made during memory
management. And, indeed, a rewritten version of the code seems to work fine:
Progressively=:1 :0
sys_timer_z_=: do_base_ bind 'N U Progressively Y'
N=:0
U=:u
Y=:y
0 u Progressively y
wd 'timer 1'
:
wd 'timer 0'
smoutput u x{y
if. (x+1)<#y do.
N=:x+1
wd 'timer 1'
else.
smoutput ' ' NB. re-issue prompt
end.
)
But I thought I should report the bug, in case someone else can get around
to isolating and fixing it before me. (I'm playing with the source version
of J but proceeding very slowly.)
(Also, of course, feel free to use the working version of 'Progressively',
if you have need of something like that.)
Thanks,
--
Raul
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