Include beat structure every bar.

lib/roborabb.rb

@@ -28,12 +28,17 @@ def to_lilypond
     def format_bars(bars, voice)
       last_bar = Bar.new({})
       bars.map do |bar|
-        preamble = if last_bar.time_signature != bar[:bar].time_signature
-          %(\\time "#{bar[:bar].time_signature}"\n)
+        preamble = ""
+        if last_bar.time_signature != bar[:bar].time_signature
+          preamble += %(\\time "#{bar[:bar].time_signature}"\n)
+        end
+
+        if last_bar.beat_structure != bar[:bar].beat_structure
+          preamble += %(\\set Staff.beatStructure = #'(%s)\n) % bar[:bar].beat_structure.join(' ')
         end
         last_bar = bar[:bar]
 
-        preamble.to_s + bar[voice]
+        preamble + bar[voice]
       end.join(' | ')
     end
 

spec/unit_spec.rb

@@ -104,7 +104,10 @@ def construct(attributes)
   describe '#to_lilypond' do
     def bar(attributes)
       double("Bar", {
-        time_signature: "4/4"
+        unit:           8,
+        notes:          {hihat: [true]},
+        time_signature: "4/4",
+        beat_structure: [4, 4]
       }.merge(attributes))
     end
 
@@ -197,5 +200,18 @@ def bar(attributes)
       bars[1].should_not include(%(\\time "1/8"))
       bars[2].should     include(%(\\time "1/4"))
     end
+
+    it 'includes beat structure changes per bar' do
+      generator = [
+        bar(beat_structure: [3, 2]),
+        bar(beat_structure: [3, 2]),
+        bar(beat_structure: [2, 3]),
+      ].each
+      formatter = described_class.new(generator, bars: 3)
+      bars = formatter.to_lilypond.split('|')
+      bars[0].should     include(%(\\set Staff.beatStructure = #'(3 2)))
+      bars[1].should_not include(%(\\set Staff.beatStructure))
+      bars[2].should     include(%(\\set Staff.beatStructure = #'(2 3)))
+    end
   end
 end