vectors.clj

(ns vectors
  (:require [clojure.test :refer [deftest is run-tests]]))

(defprotocol VectorMath2D
  (-vplus [v1 v2] "Adds two vectors"))

(defrecord Vec2D [x y]
  VectorMath2D
    (-vplus [v1 v2]
      (Vec2D. (+ (:x v1)
                 (get v2 :x 0))
              (+ (:y v1)
                 (get v2 :y 0)))))

(defn v+
  "A more general function to add 2D vectors. Takes any number of arguments,
  like +."
  ([] (Vec2D. 0 0))
  ([v] v)
  ([v1 v2] (-vplus v1 v2))
  ([v1 v2 & more] (reduce -vplus (-vplus v1 v2) more)))

(deftest addition
  (let [a (Vec2D.  3  0)
        b (Vec2D. -1 -1)
        c (Vec2D.  2  5)]
    (is (= (Vec2D. 0 0) (v+)))
    (is (= (Vec2D. 3 0) (v+ a)))
    (is (= (Vec2D. 2 -1) (v+ a b)))
    (is (= (Vec2D. 4 4) (v+ a b c)))))

(comment
  (run-tests)
  )