I'm doing AoC 2021 in Python to remember the language, and I'm enjoying contrasting how I did this in Python vs. APL:
def mark_boards(num):
for board in boards:
for i, n in enumerate(board):
if n == num:
board[i] = -n
⍝ Mark a number on a board by adding 100 to it:
mark←{(⊃⍵)∊2⊃⍵:{({100+⍵}@(⊃⍵)(⊃⍵))2⊃⍵}(⍸(2⊃⍵)∊⊃⍵)(2⊃⍵)⋄1:2⊃⍵}
That line of APL is just so funny to me. Absolutely inscrutable. Presumably I understood it while I wrote it almost a year ago? Who knows.
