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-- copypasta from https://github.com/ephemient/aoc2017/blob/master/src/Day8.hs
import Data.Map.Lazy as Map
exec :: (Num a, Ord a, Read a) => Map String a -> String -> Map String a
exec regs line
| q cond (fromMaybe 0 $ Map.lookup when regs) (read cmp)
= Map.insert reg (p op (fromMaybe 0 $ Map.lookup reg regs) (read val)) regs
| otherwise = regs where
[reg, op, val, "if", when, cond, cmp] = words line
p "inc" = (+); p "dec" = (-); q "<" = (<); q "<=" = (<=)
q "==" = (==); q ">=" = (>=); q ">" = (>); q "!=" = (/=)
day8a :: String -> Int
day8a = maximum . Map.elems . foldl' exec Map.empty . lines
day8b :: String -> Int
day8b = maximum . concatMap Map.elems . scanl' exec Map.empty . lines
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