baseball.clj

(ns baseball
  (:require [clojure.core.match :refer [match]]))

(def initial-state {:ball 0
                    :strike 0
                    :out 0
                    :error 0})

(defn rules [state]
  (match [state]
    ;; BB
    [{:ball 4}] {:ball 0 :strike 0}
    ;; 3 Outs
    [{:strike 3 :out 2}] initial-state
    ;; Out
    [{:strike 3}] {:ball 0 :strike 0 :out (inc (:out state))}
    :else state))

(defn key-for [x]
  (condp = x
    "B" :ball
    "S" :strike
    :error))

(defn calculate-score [s]
  (reduce (fn [state batting]
            (->> (update state (key-for batting) inc)
                 rules
                 (merge state)))
          initial-state
          (map str s)))

deps.edn

{:deps
 {org.clojure/core.match {:mvn/version "0.3.0-alpha5"}}
 :aliases
 {:repl {:extra-deps {com.bhauman/rebel-readline {:mvn/version "0.1.1"}}
         :main-opts ["-m" "rebel-readline.main"]}}}