aoc17.apl

⎕io←0
'display' ⎕CY 'dfns'

⍝ I replaced newlines with ` because IDK how to deal with multi-line input other than files
input ← 'x=495, y=2..7`y=7, x=495..501`x=501, y=3..7`x=498, y=2..4`x=506, y=1..2`x=498, y=10..13`x=504, y=10..13`y=13, x=498..504'

⍝ Process it into a list of points:
split ← {⍵⊆⍨~⊃+/⌽∘(⍺⍷⍵)¨0-⍳≢⍺}
sort ← {⍵[⍋↑⍵]}
fromto ← {⍺↓⍳1+⍵}
parserange ← {⊃fromto/ ⍎¨ '..' split 2↓⍵}
points ← ↑,/↑,/(∘.,/¨ parserange¨∘⌽∘sort∘(', '∘split)¨ '`'split input)

⍝ Paint them on a grid:
s← 2014 700 ⍴ 0
s[points]←1
s[⊂0 500]←2

⍝ Water physics cellular automaton
rule ← {
  (ul u ur l x r dl d dr)←,⍵
  sl←(dl∊1 6)∧(l=3)
  sr←(dr∊1 6)∧(r=3)
  (⌈/,⍵)<2 :x
  (x=0)∧(u>1)     :2
  (x=2)∧(d=1)     :3
  (x=0)∧(sl∨sr)   :3
  (x∊3 5)∧(l∊1 4) :x+1
  (x∊3 4)∧(r∊1 5) :x+2
  (x∊4 5)∧(6∊l r) :6
  (x=2)∧(d=6)     :3
  x
}

simulate ← rule⌺(3 3)⍣≡
s← 0 450 ↓ s
⎕← {'.#|~⍨⍨≈'[⍵]}¨  (rule⌺(3 3)⍣0) s