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4:36 AM
@rak1507 There was an issue with the interpreter when using a specific construct, and it could only happen with ⎕IO←0 ;-)
 
 
2 hours later…
6:34 AM
I require tips for writing complex language interpreters in APL
 
@Razetime You want to write a parser in APL?
 
yes, a parser
 
@Razetime Marshall's mini-series may be of interest, but also these items from dfns.dws and eval, min, and max.
Alternatively, you could write your language as a DSL that transpiles to APL.
 
@Adám what does this entail? I'm trying to make one for a relatively simple language
 
@Razetime If your language can have a syntax that is close to that of APL, then you can give each syntactic element a name, and (if needed) use string replacement to transpile your language to the DSL.
 
6:42 AM
hm alright
 
 
2 hours later…
8:37 AM
:58345154
 answer←'uh oh'
 :If x<0
    :Trap 0
       answer←÷x
    :EndTrap
 :EndIf
 ⎕←answer
 
8:50 AM
@MortenKromberg Sure, but the "else" block might be more than just a value, and you might not want to or be able to compute it unless the condition is false/the error is hit.
 
Understood, my answer is essentially "don't try to do that". As I understand it, you are using error trapping as PART of your validation and want to combine it with regular control structures. I do not think it is generally desirable to try to create some kind of Frankenstein monster syntax to make that easy. :OrIf is confusing enough already, imagine if it were blended with error handling...
 
Even :Finally doesn't solve this problem, does it?
 
That would depend on what you are trying to do, but not in general.
 
 
2 hours later…
11:17 AM
the comp.lang.apl newgroup is being spammed
 
12:12 PM
Does that do what you are trying, even if you don't like the technique?
:58352894 DoThis←{
    b←...
    b:DoThat ⍵
    0::DoThat ⍵
    ...
}
Ok, how do I paste in a multi-line response and have in response and have it ping properly?
 
@PaulMansour You don't. ¯\_(⍨)_/¯
I always resort to using a non-code leader line with the response tag, and then adding the code block after.
 
ok, good to know.
You've probably told me that before, but I don't comment enough to remember...
 
I don't think I have.
 
@Adám you have
 
Oh. ⍨
Added to the wiki.
 
12:18 PM
The above style is one I use a lot, though not necessarily for mixing guards and error guards. It requires naming functions, which is hard, but I think worth the effort for significant code.
 
@PaulMansour Well, kind of. You're missing the error-guarded block, which will end up separating the two paths to DoThat from each other. That's not so good.
Actually, that's not true what I just wrote.
That block is the lower ...
@PaulMansour I don't think the naming is an issue, but I still don't like having to refer to the name twice, and ToThat might need a dummy argument.
 
DoThis←{0::DoThat ⍵ ⋄ b:∘ ⋄ ...} :p
 
@dzaima Yeah, I actually asked this because I spotted such code.
 
@Adám ah. For dfns it's imo better than anything else i've seen, even if it's not nice
 
@Adám True. Neither of those issues bother me I guess.
 
12:28 PM
 
12:42 PM
Hello, I am trying to solve P1/2015 of problems.tryapl.org and I have solution that works on tryapl.org, but that gives a syntax error on problems.tryapl.org when I click on the "Test" button. It is: {d[⍋d← (a∊⎕A) / (a ← 1 ⎕C ⍺)] ≡ c[⍋ c ← (w∊⎕A) / (w ← 1 ⎕C ⍵)]}. What could be the reason that it works on one website but not on the other?
 
it may be the use of ⎕C
 
Ok, thanks! I will then search for alternatives to converting case.
 
@p.vitzliputzli 1 (819⌶) might work.
819⌶ was the old version of the ⎕C function
yep, it works.
@Adám might be a good idea to offload problems.tryapl.org's evaluation things to the newer tryAPL instead of tio
 
Yes, it worked! Thanks a lot!
 
no problem.
Feel free to come back if you have trouble with any other questions.
 
12:55 PM
Thanks, actually I am wondering if there is something like the dyadic compose (&) of J available in Dyalog APL that would allow me to do something like x u&v y ↔ (v x) u (v y). In this way I could get rid of duplicating the sorting of the characters in the left and right argument.
 
@p.vitzliputzli Yes, that is but again, only works in the newest version (including TryAPL), but not on problems.dyalog.com
 
@Adám Wonderful, thanks!
 
@p.vitzliputzli You can easily implement a model for it: Ö←{(⍵⍵ ⍺)⍺⍺(⍵⍵ ⍵)}
@Razetime Problem is that the testing framework needs unrestricted APL code, and TryAPL uses a strict whitelist.
 
@Adám Thanks!
 
1:11 PM
@Adám ah that's too bad
 
1:23 PM
@Razetime Maybe I could inject covers for and and and ⎕C and as those are easy. and a bit harder, but should be possible too. Then the only problem becomes their inverses, but that's a low cost, I think.
 
1:33 PM
7 CMCs: Dyalog 18.0's ⎕C in vanilla 17.1. Read about the enhancements here.
Announcement: Dyalog '21 will be a free online event.
2
 
1:50 PM
@Adám does this mean there will be 3 grand prize winners + 3 professional winners at Dyalog 22?
 
@rak1507 I guess.
 
2:16 PM
Yeah, I just got an email about postponing the offline event again
which is actually not bad for me because I'm not vaccinated yet (+ some other reasons)
 
2:30 PM
@Bubbler Right, my wife isn't getting her second shot until a week into September.
 
2:49 PM
@johnnynb Hey there, and welcome to the APL Orchard. Let us know if we can be of assistance with anything.
 
3:09 PM
0
Q: GNU APL how do you edit a function

johnnynbI'm having troubles figuring out how to edit a function in GNU APL. I have tried ∇func (DEFN ERROR), )edit (BAD COMMAND), )editor (BAD COMMAND) and all give me errors. Any suggestion on how to edit a simple function would be appreciated.

 
4:00 PM
To check that there are no consecutive digits in a sequence I've come up with ~∨/ 1 ¯1 ∊(¯1↓i)-(1↓i). Is there a way to write in a more compact way the (¯1↓i)-(1↓i) part? It is almost like a fork
 
you can try 2-/?
 
@Razetime Thanks. I didn't know about windowed reduced
 
4:40 PM
what's the simplest way to get the diagonals of a matrix?
 
       ,⌿(⊢⌽⍨¯1+⍳∘≢)⎕←3 4⍴⍳12
1  2  3  4
5  6  7  8
9 10 11 12
┌──────┬──────┬─────┬──────┐
│1 6 11│2 7 12│3 8 9│4 5 10│
└──────┴──────┴─────┴──────┘
 
that is cool
 
@Razetime I've bookmarked javascript:alert((location+"").replace("https://aplwiki.com/","[apl.")+"]("+location+")") so I can click it from an APL Wiki page and get markdown ready for posting in chat.
 
nice bookmarklet
 
I have a few nice bookmarklets.
 
4:45 PM
@Adám this is cool but i was thinking (9) (5 10) (1 6 11) (2 7 12) (3 8) (4)
 
@Razetime dzaima/APL
 
something shear the matrix so each row is offset by 1 and then grab columns might work?
idk
 
antidiagonals builtin?!
@hyper-neutrino yeah I guess that should be it
 
@Razetime J has that too.
@hyper-neutrino That's what APLcart's entry does, but how do you deal with the raggedness?
 
yeah... i'm not quite sure how this'd work lol.
 
4:50 PM
shear with padding element a←1+⌈/,matrix and then remove a from each
 
@Razetime Works for numeric matrices only.
 
that's what i was thinking. but then you'd need some padding element you can be sure doesn't exist
 
yeah, that's my use case
 
Total hack:
      {c/⍨×≢¨c←#~¨⍨⍪⌿(⊢⌽⍨¯1+⍳∘≢)⍵,⍨#⍨¨⍵}3 4⍴⍳12
┌─┬────┬──────┬──────┬───┬─┐
│9│5 10│1 6 11│2 7 12│3 8│4│
└─┴────┴──────┴──────┴───┴─┘
 
if it's just numeric matrices i guess you could pad with max + 1 and then remove the maximal element from all?
 
4:52 PM
don't see # everyday
 
@hyper-neutrino That's exactly what Razetime wrote.
 
oh, lol
 
maybe use ⎕DR or something to figure out type and change it up for each case
 
Crazy wasteful (though I'm not sure it is really any worse than the above), but works universally:
 
a more neat method would be to find a math expression for finding the indices of each diagonal?
 
4:54 PM
      {c/⍨×≢¨c←(⍪⌿(⊢⌽⍨¯1+⍳∘≢)⍵,⍨(⊂⍵)⍨¨⍵)~¨⊂⊂⍵}3 4⍴⍳12
┌─┬────┬──────┬──────┬───┬─┐
│9│5 10│1 6 11│2 7 12│3 8│4│
└─┴────┴──────┴──────┴───┴─┘
@Razetime Yes, but you still have to filter away the out-of-bounds locations.
 
{⍵⊢∘⊂⌸⍨⍥,+/↑⍳⍴⍵}
 
Nice.
 
woah
 
Should be added to APLcart.
 
how did you figure that out
 
4:59 PM
Now I remember Marshall doing this once.
It really makes sense.
Simply measure the distance from the top left corner.
All elements sharing distance belong to the same diagonal.
 
@Razetime from you saying to find a maths expression for the indices
and remembering the pattern +/↑⍳⍴⍵
 
I guess I'll have to remember that now
 
wait, wouldn't that (dist from topleft) give antidiagonals?
 
@rak1507 Same as +/¨⍳⍴⍵
 
@Adám faster
 
5:00 PM
@hyper-neutrino It does, but fixes that.
 
@hyper-neutrino yes, it's not quite the same as the original question
but easily adaptable
 
ah. okay
 
@hyper-neutrino should be enough to ⊖ and then run the function
 
yeah this solution is clever
 
@rak1507 (fwiw, shorter in dzaima/APL)
 
5:02 PM
@dzaima cool!
 
@dzaima Hold on, that only computes the indices, right? Doesn't return the elements.
No, wait, ⊢⌸ is dyadic. Hm.
OK, added to APLcart. Time to make dinner for the family.
 
is there a reason for ⊂⍤⊢ over ⊢∘⊂ ?
 
@rak1507 Readability. "Enclose on the right argument" vs "…deferred in preference for the enclosed…"
 
fair enough, enjoy your dinner
 
(And since it already uses , why not f⍤g…)
Thanks!
 

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