The APL Orchard

11:46 AM

@Adám will there be another CMC today? :)

@JamesHeslip Feel free to post your own too!

12:24 PM

**CMC:** A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

Stolen verbatim from projecteuler.net/problem=4

@JamesHeslip You should insert **CMC:** at the front of your message. (but that won't work with multi-line messages)

Gotcha, one second.

Is that better?

Yes, but in the future, to overcome the multi-line vs markdown issue, you can just post multiple messages in a row. They get merged automatically.

OK. I haven't actually solved this in a little while (couple years). I learnt APL by reading the Legrand book and practicing on Project Euler. I don't have any of my old solutions, but I figure this will be golfable fairly easily. Will be interesting to see what people come up with, though.

@JamesHeslip 6 bytes: 580085

@JamesHeslip You're asking for a constant answer. It isn't really interesting unless there's a parameter so the answer can vary. E.g. find the largest palindrome made from the product of two N-digit numbers.

@JamesHeslip For that, I've got ⊃⌽a/⍨(⌽≡⊢)∘⍕¨a←,∘.×⍨⊃↓∘⍳/10*⎕-1 0Try it online!

12:55 PM

Yeah, didn't really think the question through... haha. That's what I get for asking questions before lunch.

Thanks for putting a spin on it, though.

1 hour later…

1:58 PM

@Deadcode on the adjacency-matrix approach, i just tried it with the regex that tests for divisibility by 3 that you commented under the haskell solution and it works after fixing a tiny bug; on the ~140b solution that brute-forces all possible matches, i got a WS FULL (took too much memory)

@dzaima oh right, we've sacrificed ambivalency

@dzaima what are these "strands" that you and bubbler refer to in your messages here?

@KritixiLithos 1 2 3 and (1 2)(3 4) and a b c (for these names being arrays)

ah i see

@Bubbler if g wasn't a nilad, how would you have an array of g and 1?

dzaima

2 days ago, by dzaima

aka, fns as proper values = no strand notation, at which point the syntax slowly goes to k's. (not that that's a bad thing, an apl with k-ish syntax (but still unicode) is one of many apl things i'd like to attempt to make at some point)

so you're suggesting something other than strand notation to construct arrays containing functions?

dzaima

@KritixiLithos for my testing, i just used ⋄-separated arrays - (g⋄1)

2:10 PM

interesting

2:50 PM

@Adám - For a future lesson... I like the modern control structures (:IF :FOR etc), but how about covering how flow control was managed in tradAPL?

@JeffZeitlin A history lesson? It isn't really useful info other than occasionally for code golf.

Do the modern control structures allow for 'computed' branching? Similar to BASIC's ON...GOTO...?

@JeffZeitlin :GoTo Y is exactly the same as →Y and :Return is exactly the same as →

So I can write :GoTo (A=B)/LABEL1 instead of :IF A=B ⋄ :GoTo LABEL1 ?

@JeffZeitlin Yes. or even :GoTo LABEL1 LABEL2 42 LABEL3 'abc'[?4] any expression that results in a scalar or vector is fine, as along as the first element (if any) is an integer.

3:00 PM

@Adám - I like that - yeah, it's golfy and APL is not a golfing language, but handling control like that always appealed to my quirky side...

1 hour later…