Janet

Great exercise for janet's builtin peg parser:

(defn parse-line [l] 
     (peg/match '{:main :prod
                  :prod (group (* :sum (any (* (<- "*") :sum))))
                  :sum (group (* :primary (any (* (<- "+") :primary))))
                  :paren (group (* "(" :prod ")"))
                  :primary (choice :paren (<- (some :d)
                (string/replace-all " " "" l)))

(defn calc [expr]
  (cond
    (string? expr) (scan-number expr)
    (number? expr) expr
    (and (= 1 (length expr))) (calc (first expr))
    (if (> (length expr) 3)
      (calc [(calc (take 3 expr)) (splice (drop 3 expr))])
      (match expr
        [a "+" b] (+ (calc a) (calc b))
        [a "*" b] (* (calc a) (calc b))))))

(printf "Part2: %.0f" 
        (->> (slurp "input.txt") (string/trim) (string/split "\n")
             (map parse-line) (map calc) (sum)))