Conway's Game Of Life in APL (2009) [video]

I hear Algolia has an API ;)

APL was designed to be executable math notation. I think of APL programs as math formulas. You don't expect to read an unfamiliar formula and immediately understand it. You decipher it, little by little, until it clicks and you understand what it means.

APL is readable more or less like you'd read English, so it's not hard to decipher. You can find a lot of talks on the normal video-sharing sites from people like Aaron Hsu and Roger Hui demonstrating this. The modern Dyalog style of writing it is (in my opinion) a bit harder to decipher than other ways, though (at least, the style used in their public code repositories); it's much too long, and looks more or less like BASIC with symbols nowadays.

When you internalize the parsing model, it's downright trivial to read pretty much anything in it or its dialects.

Cool article, but it does go through a lot of effort (copying a string many times and then executing it) in order to get a loop on one line. In modern APL we'd just use the Power operator (⍣), which repeats a function. The dfn {⎕←Life ⍵} gets the next iteration and displays it, so {{⎕←Life⍵}⍣⍺⊢⍵} does this ⍺ times, where ⍺ is the left argument (the ⊢ is the identity function: all it does it to prevent ⍺ and ⍵ from being stranded together into one array). If we want space between the iterations, we can print an empty line first, with {{⎕←''⋄⎕←Life⍵}⍣⍺⊢⍵}. Substituting in the definition of Life, we have

  RepLife ← {{⎕←''⋄⎕←↑1 ⍵∨.∧3 4=+/,¯1 0 1∘.⊖¯1 0 1∘.⌽⊂⍵}⍣⍺⊢⍵}

Try it with

  10 RepLife ¯10 ¯10↑3 3⍴1 1 1 1 0 0 0 1 0

Another old paper on the Game of Life is Eugene McDonnell's "Life: Nasty, Brutish, and Short" (https://www.jsoftware.com/papers/eem/life.htm). This was where John Scholes got the idea of doing three rotations along each dimension. Interestingly, McDonnell attributes the idea to an implementation by Don Knuth in METAFONT!