freenode/lisp - IRC Chatlog

21:50:55 sveit I am confused how condition tests are supposed to work. Why is it that with custom condition types, '(nil) is always passed as the condition to the test? A simple failing example is: https://pastebin.com/QE87KacT

21:52:12 phoe sveit: wait a second

21:52:27 phoe '(nil)?

21:54:04 sveit phoe: i was just copying the error i get from sbcl when I run the example in my pastebin (which just defines an custom condition and a conditional restart). More precisely, sbcl complains "no applicable method for generic function test-slot when called with arguments (NIL)"

21:54:34 phoe sveit: yes, that is correct, C is allowed to be either NIL or a condition object.

21:54:39 Bike that actually means that it was called with one argument, which is nil.

21:54:45 phoe so, your function was---- exactly

21:55:09 Bike also, p hoe is right: test functions should be prepared to accept nil, and also any condition object.

21:55:12 phoe if COMPUTE-RESTARTS is called without a condition object, then restart test functions will be called with NIL

21:55:21 phoe same deal with FIND-RESTART

21:55:41 phoe if they're called with a condition object - then that argument will be that condition boject

21:55:56 phoe ...s/boject/bojack/

21:56:13 Bike you could do (and (typep c 'test-condition) (eql (test-slot c) 1)).

21:56:38 sveit ah, thanks. didn't see that in the hyperspec. seems like a strange convention, isn't compute-restarts in the usual case called without a condition object?

21:56:45 Bike the debugger might call compute-restarts without a condition, though.

21:57:15 phoe sveit: depends

21:57:36 phoe the debugger is allowed (and should) call COMPUTE-RESTARTS *with* a condition object, in particular, with the condition object that the debugger has been entered with

21:58:13 phoe it's not really specified in the spec (as the debugger isn't really specified), but it's the only logical behavior

21:58:43 sveit hmm. Doesn't seem to be the behaviour in my SBCL (that error I get was from interactively calling (test-function) in REPL)

21:58:46 phoe users are also allowed to do the same, e.g. if they end up in the debugger REPL and want to resolve the situation manually via calling FIND-RESTART and INVOKE-RESTART and what else

21:59:07 phoe what do you mean by "the behaviour"?

21:59:47 sveit phoe: i mean that the debugger seems to be calling COMPUTE-RESTARTS *without* a condition object, since nil is being passed to the condition test

22:00:31 sveit anyway thanks for your help phoe and Bike, that's much clearer

22:02:38 phoe sveit: https://plaster.tymoon.eu/view/2004#2004

22:02:46 phoe see the printouts - it is being called *twice*

22:02:54 phoe once with the condition argument, the other time, without

22:03:08 phoe you just didn't see the first case since it silently succeeded.

22:03:52 phoe there's also the issue with asynchronous printing and intertwined lines, but eh, things are still visible

22:04:18 phoe anyway, this is allowed, so a test function must be prepared to accept anything of type (OR NULL CONDITION).

22:06:23 sveit phoe: thanks for clearing that up. is there some "convention" that one should tend to return 't from the test if the condition type is null/not the type you are signaling?

22:06:42 phoe sveit: there's no convention in there

22:06:58 phoe this predicate answers the question "should this restart be visible?"

22:07:31 phoe it only gets to use two sources of information to compute the answer: the condition object or lack thereof, and the dynamic environment in which it runs

22:07:46 phoe so the answer literally depends on what the restart is supposed to do

22:08:50 phoe and whether it should be visible in all cases (when the argument is NIL) or only if specific conditions are signaled

22:09:22 phoe and even then, if these conditions have some proper internal state - you can check that by querying the slots of the condition object

22:10:02 phoe so, basically - that's a rather generic framework for restart visibility, and usually the answer will be trivial

22:10:08 phoe most of the time, simple

22:10:12 phoe rarely, complicated

22:11:22 phoe for an example, you don't want to try and offer to save a crash dump file to the default disk drive if you just got a NO-SPACE-LEFT-ON-DEVICE error mentioning that particular disk drive

22:11:47 sveit phoe: thanks for the explanation, i think i actually understand the convention now.

22:11:56 phoe or, you don't want to try and resend data on a network socket if that network socket just git a CONNECTION-RESET

22:12:07 phoe s/git/got/

22:12:33 phoe that's the general idea - the test function should answer the question of "is the restart applicable in this particular context?"

22:12:41 phoe and that's one bold and broad question

22:31:18 dsl` Hi!

22:33:32 phoe heyyy

1:12:36 ldb good morning

2:23:07 terpri__ ** NICK terpri