Quine

A quine is a program which takes no input and produces a copy of its own source code as its only output.

In APL, a quine is listed in the FinnAPL idiom library as "an expression giving itself":

      1⌽22⍴11⍴'''1⌽22⍴11⍴'''

In 2019, Nick Nikolov proposed to shorten it using the commute operator:

      1⌽,⍨9⍴'''1⌽,⍨9⍴'''

Explanation:

• '''1⌽,⍨9⍴''' the characters '1⌽,⍨9⍴'
• 9⍴ reshape to shape 9, resulting in '1⌽,⍨9⍴''
• ,⍨ concatenate with itself, resulting in '1⌽,⍨9⍴'''1⌽,⍨9⍴''
• 1⌽ rotate one character to the left, getting the characters: 1⌽,⍨9⍴'''1⌽,⍨9⍴'''

Further Entries

In 2022, APL Farm user OsKaR31415 shared the following:

      '{∊⍵⍺⍵⍺,4/⍵}'{∊⍵⍺⍵⍺,4/⍵}''''