The APL Orchard

matt

10:00 PM

hm ok. if i were to make an APL file what would it look like?

Adám

Like a mathematician went nuts :-)

RGS

@Adám +← 1000000

matt

@RGS what does that mean?!

Adám

@matt That is a way of expressing a million upvotes using an APL pun.

RGS

@matt have you seen (y) or (+1) to show support / say you agree / etc on text-based platforms? well, in here we usually use +← 1 (a play on how APL works)

so me using +← 1000000 was me agreeing a lot.

@Adám ahaha, so literal

matt

10:03 PM

i guess that makes sense. what would downvoting (-1) be then?

Adám

@matt Let's say that I have a list of measurements m. In APL I can sum them by writing +/m

@matt -←1

matt

ah of course

Adám

And doubling the score would be ×←2

I can similarly find the product of them all with ×/m

matt

so would sqrt-ing it be √←2 or something?

Adám

@matt No, that'd be the score'th root of 2.

matt

10:05 PM

what does that mean ? as you can tell i really dont know much abt apples

:)

Adám

@matt It doesn't matter. These are just puns anyway.

We can count the number of measurements with ≢m

And we can compute the arithmetic mean average with (+/m)÷(≢m)

matt

the monospace font looks terrible on my end. good job chromebooks

Adám

Increasing the font size might help a little. How does ≢ or ≢ look to you, like a slashed ≡ or like ≡ with a / next to it?

matt

like ≡ with a / next to it

Adám

Yeah, that's an annoying thing in Chrome. It is supposed to look like ≠ but with three horizontal bars.

matt

10:09 PM

screenshot:

sorry it's a bit tiny

Adám

OK, they at least touch each other so you won't confuse ≢ and ≡/

Anyway. Let's normalise the measurements in m so they add up to one: m÷+/m

matt

what does THAT mean?

Adám

It means m divided by the sum of m.

This may seem trivial, but notice that we never looped or explicitly mapped over the values of m like most languages would have you do.

matt

but wait how is m different from +/m ?

Adám

m is a list. +/m is its sum, or more precisely, + applied over m.

matt

10:12 PM

NOW I GET IT

Adám

You can apply any function f over the elements of a list with f/

matt

> future data scientist maybe, idk

note the word "future"

Adám

Where are you at now?

matt

what do you mean?

Adám

If you're a student, on what level? (You don't have to tell, of course!)

matt

10:15 PM

mind if I skip that one?

:/

Adám

No problem at all.

You know + - × ÷ from primary school, I presume.

matt

definitely

and √ and ^

Adám

Well, ^ is not really used in school, only in programming, unless you mean logical AND.

APL adds a bunch more for all kinds of nice things. E.g. a⌈b is a or b, whichever is the largest value .

matt

traditionally I'd call that ceiling(a,b)

my comma key hates me right now

Adám

Yes. But that name ceiling actually comes from APL's symbol which is a wall with a piece of the ceiling!

Similarly ⌊ is a wall with a bit of the floor, so a⌊b is that.

matt

10:19 PM

[surprised] really? never knew!

RGS

@matt wait, really? I'd call "ceiling" and "floor" to the functions that round numbers to the nearest integer (above or below) and I'd call "max" and "min" to these two functions

matt

oh right facepalm

Adám

Wait, facepalm here too. Yes.

But the things about their names is still true. It is just that ⌈a is the ceiling of a.

matt

right

Adám

APL's inventor was a mathematician, not a computer scientist, and he invented a few things that made it into mainstream mathematics. APL was his masterpiece though, for which he won an award.

matt

10:21 PM

there ya go

Adám

Now you can notice a fun thing in APL. Functions like these can be used with one argument (on the right) or with two arguments (one on each side), just like the - symbol can be used in TMN (traditional mathematical notation).

matt

right like how -4 is different from 6-4

Adám

Exactly.

matt

one is -4 and the other is 2

Adám

Yes. The first is the negate function and the second is the subtract function.

matt

10:23 PM

"let's learn math kids! but with really cool symbols and things!"

Adám

Yup.

Fredrik Niemelä

:)

Adám

APLers call one-argument functions "monadic" and two-argument functions "dyadic".

matt

makes sense. I just made myself a google docs thing that replaces "sqrt " with "√"

Adám

Often, the two meanings of a symbol are closely related. E.g. -a is the same as 0-a

matt

10:24 PM

right right

Adám

In APL, you can also use ÷ monadically like ÷a and it is the reciprocal, i.e. 1÷a

matt

hm interesting. should I be taking notes?

Adám

You don't have to. You can find all this quite easily.

Actually, now you already know most of the types of pieces that APL is built from.

matt

prob'm is the wikipedia article en.wikipedia.org/wiki/APL_syntax_and_symbols doesn't make much sense at all

Adám

@matt I know. aplwiki.com is much better.

matt

10:27 PM

interesting

Adám

A really nice thing in APL is that all the normal built-in functions have symbols. There are no reserved words.

matt

hm

Adám

This means that you don't have to "be a programmer" that knows all the reserved words to avoid problems. There simply aren't any.

matt

think my"few minutes" are up :/

Adám

@matt No problem. I should go to bed too. I hope I whetted your appetite for more. You're always welcome back.

matt

10:30 PM

bed at 3:30pm?

Fredrik Niemelä

@Adám do you have time for one more quick Q?

RGS

@matt ahaha, we are in different time zones

matt

yep

Adám

@matt It is 11:30pm by RGS and me :-)

@FredrikNiemelä I can't resist. Go ahead!

matt

ah so you guys are in *timezone lookup* London?

Adám

10:32 PM

I'm in London. My location is in my user profile too.

matt

i'm ~halfway across the planet in vegas

Fredrik Niemelä

∇f
{⎕←1↓0⍕|-/⍎⍵}⍞
→1
∇
f

mostly solves the problem "different" and needs no EOF. But the *first* output row is "right justified" (or maybe just has a bunch of spaces prepended). Why is that?

matt

wow what is that??!

Fredrik Niemelä

@Adám (That's basically your code from earlier)

Adám

@FredrikNiemelä A bug really. It wasn't like that in 17.1. That's why I redirected stderr to null in my email.

Fredrik Niemelä

10:34 PM

Ah... let me try that...

RGS

@matt Portugal, here :) but same TZ as London

Fredrik Niemelä

Yep... that fixes it

matt

ah ok

Fredrik Niemelä

We will only be capturing stdout (and ignoring stderr) anyway... so yay... we have a solution.

Adám

(What is actually happening is that the interpreter prints a few spaces for you to enter the lines of your function. Of course, this doesn't make any sense when in -script mode.)

matt

10:35 PM

ok guys gotta go

Adám

@matt Bye ○/

Fredrik Niemelä

@Adám Now is this terribly unidiomatic APL?

RGS

@matt bye! Hope to see you back in the future!

Fredrik Niemelä

...I mean the goto doesn't feel great

matt

you ... might. hopefully

Adám

10:36 PM

@FredrikNiemelä Not really. I'd not use hard-coded line numbers, and there are more elegant ways of doing it.

Fredrik Niemelä

Ok... good. But at least we know it's possible.

Adám

As long as you don't have a problem where one needs to capture an unknown number of lines, and then process them, yes.

Fredrik Niemelä

Can't promise that there are none.... but it's not very common at least

Adám

{⎕←1↓0⍕|-/⍎⍞}⍣{0}⍬ should work. As should {∇⎕←1↓0⍕|-/⍎⍞}⍬

I.e. you don't need that wrapper function at all.

RGS

@Adám ...⍣(0⍨)⍬ ?

Fredrik Niemelä

10:39 PM

Yes, both of those works... but only if you add an explicit newline to the file

Adám

@RGS Heh, yes, but that's longer.

RGS

@Adám I know, but looks cooler!

Adám

@FredrikNiemelä Where do you mean, after that line? Or in the input?

Fredrik Niemelä

@RGS could you explain to the noob? (i.e. me)

Adám

@FredrikNiemelä It is a new language feature in 18.0 that value⍨ is a constant function.

Fredrik Niemelä

10:40 PM

@Adám after the line in the source file

Adám

@FredrikNiemelä So it needs TWO trailing newlines?

Fredrik Niemelä

No, just one

RGS

@FredrikNiemelä I'm a noob too haha; {0} is a constant function and I replaced it with another constant function, new in 18.0

matt

well i came back

Fredrik Niemelä

@RGS Ah... I agree that it looks cooler :)

not that that is a good metric :)

Adám

10:42 PM

@FredrikNiemelä Oh, but according to the POSIX standard (which Linux follows) a non-empty file must have a trailing newline. Otherwise it is an invalid file.

@matt That was quick.

RGS

@Adám oh wow

matt

@Adám heh

Adám

1397

A: Why should text files end with a newline?

Because that’s how the POSIX standard defines a line: 3.206 Line A sequence of zero or more non- <newline> characters plus a terminating <newline> character. Therefore, lines not ending in a newline character aren't considered actual lines. That's why some programs have problems pro...

Fredrik Niemelä

@Adám Right, I don't disagree

@Adám btw the earlier solution with trailing EOT required a trailing newline after the EOT to work... which is both correct and very broken

Adám

@FredrikNiemelä Right, because the EOT didn't actually terminate anything, it was just a very unlikely line I could recognise.

Fredrik Niemelä

10:47 PM

Right

Adám

Btw, will you ever have empty input lines?

Fredrik Niemelä

I mean... it could happen I guess, but I don't know of any such cases...

Maybe when an input line is a literal string and the empty string is an allowed input?

Would that break things?

Adám

No, I was just thinking that one could stop asking for more input when getting an empty input.

Fredrik Niemelä

But you would never get empty input because there would (normally) be only one trailing newline, not two

matt

think I ate too many apples

Adám

10:50 PM

⍞ really doesn't care. It eats everything until the next newline, even control characters.

@FredrikNiemelä True, but it could be used as a light-weight convention.

Fredrik Niemelä

I was considering using the ⍞ with timeout... but that's kinda ugly

Adám

@matt Just wait until you begin consuming APL pi: ○

matt

how is THAT pi?

Adám

@FredrikNiemelä And it resolution isn't good enough. Currently the minimum timeout (using the built-in method anyway) is 1 second. I'm considering asking for that to be enhanced to handle fractional seconds.

matt

but srsly I love apple pie

Adám

10:52 PM

@matt That's just another of APL's symbols. Monadic (one-argument) ○ is "pi times", so ○2 is 6.283185307

matt

aka tau

Adám

Yup.

The symbol is of course a stylised pie seen from directly above.

Fredrik Niemelä

@Adám Do you think the APL devs would be against adding support for reading until end of stream?

matt

@Adám i doubt that

Adám

(Also, but that's secondary, in my opinion, it symbolises that pi is the fraction between the circumference and diameter of a circle.)

Fredrik Niemelä

10:54 PM

@Adám I don't think we need it, but IMO it really should be supported.

Adám

@FredrikNiemelä No, not at all. In fact I know it, because I spoke with our chief architect about it today. This is something I'm sure we'll address in 19.0.

matt

"we"?

Fredrik Niemelä

+← 1

(Did I do that right?)

matt

looks like it

Adám

@matt I help develop the language.

matt

10:55 PM

cool!

Fredrik Niemelä

@Adám when is 19.0 expected?

Adám

In a year. We just released 18.0.

Fredrik Niemelä

+← 1

Adám

@FredrikNiemelä Btw, you do realise why that is taken as "upvote", right?

Fredrik Niemelä

Yes

But thanks for checking :)

Adám

10:59 PM

People often forget that APL's modified assignment is completely general, and you can use any function to the left of ←. Sometimes the main code can live there.

Fredrik Niemelä

Yes... my son has been using that for some of his recent APL code...

...for the untrained eye it feels jarring

Adám

      v←3 1 4 1 5 9 2 6 5 4
      v{⍺/⍨⍺<⍵}←5
      v
3 1 4 1 2 4

Hey, now with 18.0 we can even do

      v←3 1 4 1 5 9 2 6 5 4
      v(<⊢⍤/⊣)←5
      v
3 1 4 1 2 4

Fredrik Niemelä

wait what? I got the first one...

Adám

@FredrikNiemelä If you're going by Mastering Dyalog, then you've not met trains yet.

Fredrik Niemelä

sideways T is identity, right?

/ here is replicate?

Adám

11:02 PM

Yes and yes.

Fredrik Niemelä

Oh...

so less-than-same atop replicate-same ?

Adám

@FredrikNiemelä No, less-than same-atop-replicate left

Operators bind first. So ⍤ binds ⊢ and /

Fredrik Niemelä

Ah... yes... and that makes more sense

matt

now what is happening?!!

Fredrik Niemelä

@matt well...
we're talking through v(<⊢⍤/⊣)←5

matt

11:06 PM

[eyeroll] and what does that mean?

Fredrik Niemelä

first...
val anyfunc←otherval simply means

val ← val anyfunc otherval

matt

I... I give up

Adám

@matt It means filter the variable v in-place, preserving only elements less than 5.

Fredrik Niemelä

like a += b is a = a + b in many languages

matt

I still give up

Fredrik Niemelä

11:07 PM

Do you know C++?

matt

nope

Fredrik Niemelä

Ah

What languages do you know?

Adám

@FredrikNiemelä (Should have been called ++C imo)

matt

js & html are basically it

Fredrik Niemelä

Well js, does have +=

matt

11:08 PM

true

Adám

But even JavaScript allows v=42; v+=1

Fredrik Niemelä

a += b
in javascript means
a = a + b

matt

yes

Fredrik Niemelä

In APL the + can be any function

Adám

And the assignment is ← not =

matt

11:09 PM

@Adám which makes v=43

Fredrik Niemelä

so
a myfunction= b
would be
a = a myfunction b

matt

ohhh i get it

Fredrik Niemelä

but also... as @Adám said. = is ←

soooo

Adám

@matt Yes, and so to in APL:

matt

why the indent?

Fredrik Niemelä

11:10 PM

v(<⊢⍤/⊣)←5
means
assign v function 5 to v

Adám

In interactive mode (a REPL) it is customary to indent user input 6 spaces and have output flush left.

matt

also how crazy is apl syntax highlighting?

Fredrik Niemelä

where function is that stuff in the middle "<⊢⍤/⊣"

matt

right

Fredrik Niemelä

Hmm.. I've never seen APL syntax highlighting. @Adám what does it look like?

Now.. the funtion here is actually 3 functions connected together

<
⊢⍤/
⊣

Adám

11:12 PM

You can see coloured APL on TryAPL.

Fredrik Niemelä

@Adám A right... sorry I retract my statement and claim the opposite

Adám

That's a bit over the top on happy colours for my taste, but in an actual IDE you can choose or design your own scheme.

Fredrik Niemelä

:)

Adám

Fun fact: APL can syntax colour itself.

matt

whaaaaaat? how!

Fredrik Niemelä

11:13 PM

@matt
The first function < return true booleans for all places where v is less than 5

yes... whaaaat?

Sorry guys I need to head out...

matt

(was referring to how apl can color itself)

Fredrik Niemelä

yes... me too :)

@Adám can probably continue to explain the code better than I can. I've only known the language for a week or two.

matt

oh uh

a week?!

Fredrik Niemelä

...or two

Adám

@matt Yes, it is really easy to learn.

matt

11:15 PM

for you!

Fredrik Niemelä

It's really hard at the very beginning. since it just looks like greek

matt

i couldn't agreemore

Fredrik Niemelä

But when you understand the basics it all makes complete sense quite quickly

matt

agree more

Adám

APL colouring APL:

Fredrik Niemelä

11:16 PM

Anyway.... gottago!

Adám

      code←'∇foo' 'v←3 1 4 1 5 9 2 6 5 4' 'v{⍺/⍨⍺<⍵}←5' '∇'
      cols←200⌶code
      ↑code⍪⍤,¨¨cols
┌───┬───┬──┬──┬──┬──┬──┬──┬───┬──┬─┬─┬─┬─┬─┬─┬─┬─┬─┬─┬─┐
│  ∇│ f │ o│ o│  │  │  │  │   │  │ │ │ │ │ │ │ │ │ │ │ │
│180│21 │21│21│0 │0 │0 │0 │0  │0 │0│0│0│0│0│0│0│0│0│0│0│
├───┼───┼──┼──┼──┼──┼──┼──┼───┼──┼─┼─┼─┼─┼─┼─┼─┼─┼─┼─┼─┤
│v  │ ← │3 │  │1 │  │4 │  │1  │  │5│ │9│ │2│ │6│ │5│ │4│
│7  │19 │5 │5 │5 │5 │5 │5 │5  │5 │5│5│5│5│5│5│5│5│5│5│5│
├───┼───┼──┼──┼──┼──┼──┼──┼───┼──┼─┼─┼─┼─┼─┼─┼─┼─┼─┼─┼─┤

doesn't work for me

@matt Where? TryAPL?

yeah

No, TryAPL is very limited. You can download the full system from here.

matt

11:20 PM

doesn't support my lil chromebook :(

Bubbler

Or Try it online!

though it doesn't have latest features of 18.0

Adám

@Bubbler You're so much quicker than me!

matt

what do the boxes and numbers mean in the output?

Bubbler

First line in each box is the character in the code, and the number below it is the color code

matt

in... deciaml?

decimal

Bubbler

11:23 PM

Yes

Adám

It is actually better than a colour code. It is a code for what syntactic role that character has.

matt

more bad monospace

and what is a syntactic role and their codes?

Bubbler

e.g. number literal has code 5, function name foo has code 21

Adám

We can even ask APL that too:

      5{⍵[⍵[;2]⍳⍺;1 3]}201⌶0
┌────────────┬───────┐
│Global token│MINI_NC│
└────────────┴───────┘

Number 5 is a global token, namely a Numeric Constant that was identified by the "mini-scanner".

matt

this is a very deep rabbit hole

Adám

11:27 PM

      21{⍵[⍵[;2]⍳⍺;1 3]}201⌶0
┌────────────┬──────────┐
│Global token│MINI_FNAME│
└────────────┴──────────┘

21 is a global token, namely a Function NAME identified by the mini-scanner.

Bubbler

My guess was right :)

matt

1=comment
2=UCC?

Adám

Btw, there's are a couple of puns here too.

matt

3=white

4=CC

Adám

UCC: Unicode Character Constant if I recall right.

matt

11:29 PM

"white"?

Adám

whitespace

matt

"CC"?

Adám

(single-byte) Character Constant

But mind you, you never need to use these codes, unless you're doing some serious "meta-programming".

matt

so how do the codes do syntax hilighting?

Adám

You can use them to assign classes to <span>s.

matt

11:32 PM

HTML + APL ?!!

Adám

That's what we did here (click "View: APL code")

Yeah ^ is a website defined in APL (as you can see by viewing the code behind it) running on a webserver that's also written purely in APL.

matt

what's that amazing font?

Avi F. S.

Are there any helpful funcs or techniques for maneuvering around through a matrix in APL? For instance for maze games/solving, if you want to take numerous steps, each time remembering your current position, and then 'moving' accordingly as a function of your neighboring cells...

Adám

@matt That's what happens if you use a proper font instead of the ChromeBook's default.

Avi F. S.

At the moment, all I can think of to help is the stencil primitive, but its usefulness is limited here

Adám

11:35 PM

@AviF.S. I'd just remember the current position and then chop around that to get the neighbours if needed.

matt

is it APL385?

Adám

Yes.

@matt You can find it and more here.

Avi F. S.

@Adám By chopping do you mean ↑↓?

Adám

@AviF.S. Yes.

Avi F. S.

There must be a better way, no?

Also, that begs a tradfn which I'm trying very hard to avoid...

Trying to think of a slightly less procedural way, if possible

Adám

11:38 PM

@matt Here's the code that created the syntax colouring you see on the website.

Bubbler

@AviF.S. One way is to model the game states as a graph and throw in shortest path etc.

matt

so what things are what colors?

Avi F. S.

@Bubbler Good idea for an actual maze solver. Unfortunately, it's not quite what I'm trying to do, just the closest analog I could think of...

Anything that can thoughtfully trace through a matrix (by 'thoughtfully' I mean step through in a manner dictated by its neighbors at each step), is what I'm looking for

Any mechanism that'll neatly allow that, I mean

Adám

@matt CSS here.

Bubbler

> step through in a manner dictated by its neighbors at each step

Avi F. S.

11:43 PM

I thought there might be more stencil-like tools in the library I was missing that one could perhaps use to run the logic on the matrix all at once, first. Before then tracing through it (if that makes sense)...

@Bubbler What about that?

Bubbler

Then you can compute the next move for every position in the matrix beforehand

matt

@adan hm

Avi F. S.

@Bubbler Exactly! That's what I'm doing with ⌺

But I still need a way to then trace through it, and I'm really trying very hard to not utilize the tradfn constructs. But I'm afraid I'll have to use a while loop...

Bubbler

And then a graph search algorithm will automatically find you the path you'll take

Avi F. S.

@Bubbler But there's no question as to what the correct path is. I don't have to find the best one from several, nor optimize.

I just have to follow the 'instructions' as given by the neighbors, to trace through once

In a particular fashion

So I'm afraid graphs won't work. Really it's just a while loop that updates a pointer with the current position until it's at the end

Bubbler

11:47 PM

If you have only one possible step at every position in the matrix, the path will be definitely linear, but you still need to compute it

Avi F. S.

Just hoping there's a purer APL way to do that, because I distrust :Constructs deeply

Bubbler

And a linear path is still a graph.

matt

where are all the apl things in unicode?

Marshall

@matt Miscellaneous technical mostly.

Bubbler

Miscellaneous Technical

Miscellaneous Technical is a Unicode block ranging from U+2300 to U+23FF, which contains various common symbols which are related to and used in the various technical, programming language, and academic professions. For example: Symbol ⌂ (HTML hexadecimal code is ⌂) represents a house or a home. Symbol ⌘ (⌘) is a "place of interest" sign. It may be used to represent the Command key on Mac keyboard. Symbol ⌚ (⌚) is a watch (or clock). Symbol ⏏ (⏏) is the "Eject" button symbol found on electronic equipment. Symbol ⏚ (⏚) is the "Earth Ground" symbol found on...

matt

11:50 PM

mostly?

Avi F. S.

@Bubbler Hmm... I'm not really sure that's an efficient use of resources, though. It'd take far more ingenuity and complexity to convert it than to solve as is...

Adám

@matt Lots of plain ASCII in use too.

Marshall

@matt Stuff like ≤ that's not specific to APL is elsewhere.

Bubbler

@AviF.S. Then a simple ⍣-loop should do.

Avi F. S.

@Bubbler Oh my god, what an idiot!

matt

11:52 PM

@adam hm

Avi F. S.