Implement abs-pitch and sketch out pitch

src/music.clj

@@ -34,21 +34,6 @@
           {:duration 1/4, :pitch [:G 3]}
           {:duration 1/4, :pitch [:A 3]}]])
 
-;; TODO exercise 2.1 (ii-V-I function)
-;; this will involve being able to answer, "what pitch is n semitones above this one?"
-
-(def ii-V-I
-  (let [Dm [:= (note 1 [:D 4])
-               (note 1 [:F 4])
-               (note 1 [:A 4])]
-        Gmaj [:= (note 1 [:G 4])
-                 (note 1 [:B 4])
-                 (note 1 [:D 5])]
-        Cmaj [:= (note 2 [:C 4])
-                 (note 2 [:E 4])
-                 (note 2 [:G 4])]]
-    [:+ Dm Gmaj Cmaj]))
-
 (defn note [duration pitch]
   {:duration duration, :pitch pitch})
 
@@ -70,5 +55,40 @@
 (defn player [player-name music]
   [:modify music {::player player-name}])
 
-(defn keysig [pitch mode music]
-  [:modify music {::keysig [pitch mode]}])
+(defn keysig [pitch-class mode music]
+  [:modify music {::keysig [pitch-class mode]}])
+
+(defn pc-to-int [pitch-class]
+  (case pitch-class
+    :Cbb -2 :Cb -1 :C 0 :C# 1 :C## 2
+    :Dbb 0 :Db 1 :D 2 :D# 3 :D## 4
+    :Ebb 2 :Eb 3 :E 4 :E# 5 :E## 6
+    :Fbb 3 :Fb 4 :F 5 :F# 6 :F## 7
+    :Gbb 5 :Gb 6 :G 7 :G# 8 :G## 9
+    :Abb 7 :Ab 8 :A 9 :A# 10 :A## 11
+    :Bbb 9 :Bb 10 :B 11 :B# 12 :B## 13))
+
+(defn abs-pitch [pitch-class octave]
+  "Returns the absolute pitch of a pitch class at an octave"
+  (+ (* 12 octave) (pc-to-int pitch-class)))
+
+;; TODO
+(defn pitch [abs-pitch]
+  "Returns the pitch class and octave represented by the absolute pitch.
+   In cases of enharmonic equivalence, returns the sharp rather than the flat."
+  ())
+
+;; TODO exercise 2.1 (ii-V-I function)
+;; this will involve being able to answer, "what pitch is n semitones above this one?"
+
+(def ii-V-I
+  (let [Dm [:= (note 1 [:D 4])
+               (note 1 [:F 4])
+               (note 1 [:A 4])]
+        Gmaj [:= (note 1 [:G 4])
+                 (note 1 [:B 4])
+                 (note 1 [:D 5])]
+        Cmaj [:= (note 2 [:C 4])
+                 (note 2 [:E 4])
+                 (note 2 [:G 4])]]
+    [:+ Dm Gmaj Cmaj]))