Kata: Back to the Checkout in Clojure

I just did the Back to the Checkout kata.

These are the tests using Midje:

	(ns back-checkout.core-test
	(:require
	[midje.sweet :refer :all]
	[back-checkout.core :as checkout]))
	(facts
	"about the checkout system"
	(let [prices-by-good {:A {:unit-price 50
	:special-prices {3 130}}
	:B {:unit-price 30
	:special-prices {2 70}}
	:C {:unit-price 100
	:special-prices {3 200}}
	:D {:unit-price 500
	:special-prices {2 600}}
	:E {:unit-price 80}}
	price (partial checkout/price prices-by-good)]
	(fact
	"the price for zero goods is 0"
	(price "") => 0)
	(fact
	"one unit of a good costs its unit price"
	(price "A") => 50
	(price "B") => 30)
	(fact
	"one unit of several goods cost the sum of their unit prices"
	(price "AB") => 80)
	(fact
	"several units of a good cost the sum of its unit prices
	if there is no special price for the given amount of goods"
	(price "AA") => 100)
	(fact
	"several units of a good cost the special price
	for the given amount of goods"
	(price "AAA") => 130)
	(fact
	"several units of goods with and without special prices"
	(price "AAABBBCCCDE") => 1000)))

view raw back-checkout_test.clj hosted with ❤ by GitHub

and this is the resulting code:

	(ns back-checkout.core)
	(defn sku [c]
	(keyword (str c)))
	(defn unit-price [prices-by-good good-sku]
	(get-in prices-by-good [good-sku :unit-price] 0))
	(defn regular-price [prices-by-good [good-sku amount]]
	(* amount (unit-price prices-by-good good-sku)))
	(defn special-price [prices-by-good [good-sku amount]]
	(get-in prices-by-good [good-sku :special-prices amount]))
	(defn good-price [prices-by-good ordered-goods]
	(or (special-price prices-by-good ordered-goods)
	(regular-price prices-by-good ordered-goods)))
	(defn price [prices-by-good goods]
	(->> goods
	(map sku)
	frequencies
	(map #(good-price prices-by-good %))
	(reduce +)))

view raw back-checkout.clj hosted with ❤ by GitHub

I did a mix of TDD and playing in the REPL to solve it.

You can check commits step by step here.

You can find all the code on GitHub.