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dzaima
dzaima
10:02
@dzaima also ⌽,/,\↓⍬2⍴⌽⍳10
Torsten Grust
Torsten Grust
10:35
⍬2⍴...? Useful!
dzaima
dzaima
11:10
it's my implementation of the ¯1 talked about a bit above here. ⍬ isn't the best thing to use for that, but imo it's better than using up the whole negative domain (even if negatives aren't used currently)
it also can be used without spaces, but for how useful ⍬2⍴ is, i think even 3 chars is a bit much
Torsten Grust
Torsten Grust
11:55
Ah, I see now.
I fully agree regarding the utility of the construct. Have found myself counting the length of the input, instead. Not nice.
 
1 hour later…
Adám
Adám
13:22
@dzaima I think it should be ∞ so that the negatives can reverse fill of axes. Btw, why doesn't ⊖[1 2]mat or ⊖⍤(⊂1 2)⊢mat work? It should clearly be ⌽⊖mat…
dzaima
dzaima
13:39
@Adám infinity could also cause issues - it's there for edge-cases after all
⍬ also has the property ∧/∊⍬2=4 2
Adám
Adám
13:53
@dzaima I'm not sure I understand why that is useful.
dzaima
dzaima
@Adám it easily allows testing whether a shape with empty dimensions matches an actual shape. I don't know when that'd be helpful, but it exists
Adám
Adám
@dzaima Ah, I see. However using ⍬ uses up the entire nested domain. E.g. 2(2 4)⍴⍳6 could mean [1 2 0 0 ⋄ 3 4 5 6]. Not sure how useful that is, but…
dzaima
dzaima
@Adám yeah, everything except some null type is gonna have consequences
Adám
Adám
@dzaima Well, there are also various variations, like combining "fill" with reverse, and strict/round-up-and-pad/round-down/round-up-and-recycle.
dzaima
dzaima
@Adám imo everything except strict there is useless (maybe also not reverse, but it doesn't feel too useful either), but that's just my opinion
 
2 hours later…
RosLuP
RosLuP
16:34
Error value must have one value out the range of possible right results, each operation that has the error value has to return the error value, each function that has one argument the error value, or in its argument there is one error value, has to return the error value...
Adám
Adám
17:33
@RosLuP Except if an error causes an actual error instead of an error value. E.g. 2÷0 can either return NaN or actually error.
 
2 hours later…
RosLuP
RosLuP
19:20
NaN is perfect as error value, at last I think that...possible codified in a character... So the program can continue, and if some output is request one know it is incorrect when see that the program print Nan as result...
Adám
Adám
@RosLuP Then what happens if the vector Vec containing has 1 NaN 3 and Res←+/1 0 1/Vec? What should Res become? 4 or NaN?
RosLuP
RosLuP
@Adám when + meet Nan it return Nan so the result for me will be Nan...so +/ 1 0 1 1 Nan 3 for me it has to return Nan...
Adám
Adám
@RosLuP Yes, but how about +/1 0 1/1 NaN 3 ?
RosLuP
RosLuP
@Adám yes that not use NaN...if not use they value it would be 4... 1 0 1/1 Nan 3 return 1 3 so +/1 3 would return 4 because not use one error value...
Adám
Adám
@RosLuP So you're saying that +/1 0 1/1 2 6÷1 0 2 should give 4?
RosLuP
RosLuP
19:32
In few words all variable are not build on Nan should be ok even if in the program there is some Nan
Adám
Adám
@RosLuP Isn't that a bit dangerous? You might not notice that something is terribly wrong in your program.
RosLuP
RosLuP
The result build without error are ok...if some collateral calculation give Nan but it is not used for the result should be ok too
Yes I say +/1 0 1/1 2 6 div 1 0 2 (if 1 0 1/ means choose only first and last) should return 4
dzaima
dzaima
@RosLuP in my opinion code should always error at the earliest time possible always, because relying erroring operations pretty much always means bad code - e.g. that code should replicate before dividing
Adám
Adám
@dzaima That's just that particular example, but the compress (/) may not be possible until after the potential error-inducing operation.
RosLuP
RosLuP
For me one has to be sure only the chain or the path from initial values thru all operation that effectively give the result
dzaima
dzaima
19:44
@Adám I understand that that example was exaggerating, yes, but in general, if you're dividing by zero there are two options - either you wanted that or didn't. If you didn't, an error would most definitely be appropriate. If you did, well you could've just not divided by zero if you knew the outcome..
Adám
Adám
@dzaima Of course, but this was to make the point that inserting a NaN and continuing with code that may then later discard the NaN can be dangerous.
RosLuP
RosLuP
if there is one zero division and the program drive one machine or one aviation it can not stop...it has return one wrong value and the machine has to run in the error path...
For me if Nan is not used: It is ok
Adám
Adám
@RosLuP I think that it would be safer for the control system to signal that it has hit an error than to command that the servo motor rotate NaN (or a complex number of) degrees…
dzaima
dzaima
@RosLuP for me NaN shouldn't exist, as using it at any point in time is gonna be only a waste of CPU
RosLuP
RosLuP
In a perfect word Nan or the error value should not exist...but in programming are the input can be out of consented value, div 0, overflow numbers, memory exhaust...so it return Nan...
are==area ^ above
Adám
Adám
19:58
@RosLuP (you can edit your messages)
dzaima
dzaima
@RosLuP in my opinion, if you want to have explicit error values, make explicit error values. They can be useful, but being everywhere I feel they do way way more harm than help
Adám
Adám
@RosLuP Or throw an error. As far as I know, no APL which uses the name "APL" has NaNs.
dzaima
dzaima
@Adám does my APL count as using the name APL, because it definitely has NaNs (only because I haven't bothered removing them though)
Adám
Adám
@dzaima As far as I knew, then. But they are unintentional, right? Now I think of it, Dyalog also has NaNs, but only because we don't sweep for NaNs.
dzaima
dzaima
@Adám yeah, they are unintentional, and it'd probably harm performance a lot in Java to detect NaNs
ngn
ngn
20:17
devil's advocate: all floating point, including NaN, is wrong and evil, but given it already exists in hardware, why not make the most of it performancewise?
dzaima
dzaima
@ngn I agree, floating point sucks, but as the alternative is doing a lot of unnecessary work, it's used
i really don't know the details, but doesn't x86 allow deciding what happens with erroring actions without harming performance otherwise?
ngn
ngn
@dzaima for sse the mxcsr register controls that
ngn
ngn
20:44
see also man feenableexcept

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