Begin implementing (perform)

src/performance.clj

@@ -1,4 +1,15 @@
-(ns performance)
+(ns performance
+  (:require [clojure.core.match :refer [match]]))
+
+;; A player is an entity that knows how to interpret music in a certain ways
+;; I need to flesh most of this out -- see section 8.3 on page 141
+(def a-player
+  {:name "player1"          ;; player name
+   :play-note
+   (fn [context note] ())   ;; function to play a note with a context, returns Performance
+   :interp-phrase
+   (fn [p-map context attrs music]) ;; function to interpret a Music value, returns performance
+   :notate [context note]}) ;; function to transcribe a note - not implemented in Euterpea
 
 ;; A performance is a data structure that describes the act
 ;; of performing a piece of music. It is a vector of events,
@@ -17,13 +28,41 @@
 ;; changing tempo, key signature, tempo, etc.
 (def my-context
   {:time 0              ;; time at which the performance starts in seconds
-   :player {:?? :??}    ;; not sure what this is
+   :player a-player     ;; player currently interpreting the music
    :instrument "Cello"  ;; instrument currently playing (?)
    :duration-t 2        ;; the duration in seconds of a whole note
    :pitch-offset 0      ;; a pitch offset -- number of semitones to transpose notes up or down
    :volume 50           ;; volume of performance
    :key [:C :major]})   ;; current key signature
 
+(defn perform
+  "Convert a music value to a performance value"
+  [player-map context music]
+  (first (perf player-map context music)))
+
+(defn perf
+  "Implementation of perform, returns a tuple of (performance, duration)"
+  [player-map context music]
+  (let [{:keys [player duration-t]} context]
+    (match music
+          {:duration duration
+           :pitch pitch} (apply (:play-note player)
+                                context
+                                duration
+                                pitch
+                                (* duration duration-t))
+          {:duration duration} [[] (* duration duration-t)]
+          [:+ & ms] (reduce (fn [[events-acc dur-acc] m]
+                              (let [[events dur] (perf player-map
+                                                       context
+                                                       m)]
+                                [(concat events-acc dur-acc)
+                                 (+ dur-acc dur)])) 
+                            [[] 0]
+                            ms)
+          [:= & ms] :TODO
+          [:modify control m] :TODO)))
+
 (defn metro
   "Generates a duration-t value (the duration in seconds of a whole note)
   from the number of beats per minute and the duration of a beat (1/4 for