Implement (dur)

project.clj

@@ -1,2 +1,4 @@
 (defproject clojure-school-of-music "0.1.0"
-  :dependencies [[overtone "0.10.3"]])
+  :dependencies [[org.clojure/clojure "1.8.0"]
+                 [org.clojure/core.match "0.3.0-alpha5"]
+                 [overtone "0.10.3"]])

src/music.clj

@@ -1,4 +1,5 @@
-(ns music)
+(ns music
+  (:require [clojure.core.match :refer [match]]))
 
 ;; an octave is an int, e.g. 4
 ;; a pitch class is a keyword from :Abb to G##
@@ -109,3 +110,16 @@
       (if (> (abs-pitch p) (abs-pitch max-ps))
        p
        max-ps))))
+
+(defn dur
+  "Computes the duration of the music value"
+  [music]
+  (match music
+         {:duration d} d
+         [:+ m & ms] (+ (dur m) (dur (into [:+] ms)))
+         [:+] 0
+         [:= & ms] (apply max (map dur ms))
+         [:=] 0
+         [:modify {:tempo r} m] (/ (dur m) r)
+         [:modify _ m] (dur m)))
+