Quine: Difference between revisions

In 2022, [[APL Farm]] user OsKaR31415 shared the following:<ref>[https://discord.com/channels/821509511977762827/821511138184396840/976205210580037662 Transcript for 2022-05-17] – [[APL Farm]]</ref>

Explanation:

 

In this code, the main function is <source lang=apl inline>{∊⍵⍺⍵⍺,4/⍵}</source> with the right argument <source lang=apl inline>⍵</source> being single quote literal (spelled with four quotes, <source lang=apl inline>''''</source>, because single quotes delimit APL character literals, and quotes inside such must be doubled), and the left argument <source lang=apl inline>⍺</source> being the character vector representation of the function (<source lang=apl inline>'{∊⍵⍺⍵⍺,4/⍵}'</source>).

 

The idea behind this quine is that the only thing you need to have a string containing the original code is to reproduce this structure: [quote] [function] [quote] [function] [quote] [quote] [quote] [quote]. This is precisely what the function does. Given the representation of a function <source lang=apl inline>⍺</source> (itself in this case), and character <source lang=apl inline>⍵</source> (here, the quote), it produces the structure <source lang=apl inline>⍵ ⍺ ⍵ ⍺ ⍵ ⍵ ⍵ ⍵</source>. A more explicit version would be <source lang=apl inline>'{⍵,⍺,⍵,⍺,⍵,⍵,⍵,⍵}'{⍵,⍺,⍵,⍺,⍵,⍵,⍵,⍵}''''</source> which simply concatenates together the required parts. The original quine is very similar, only using the shorter <source lang=apl inline>4/⍵</source> to produce the 4 occurrences of <source lang=apl inline>⍵</source>, and [[code golf|golfs]] away the spaces, instead opting for [[Enlist]] (<source lang=apl inline>∊</source>) to flatten the intermediary [[nested array]].