Add motifs including arpeggios (#6)

src/motifs.jl

@@ -0,0 +1,58 @@
+
+# A motif is a repeating pattern within a scale
+# Specify by how many scale notes to increment for each subsequent note
+
+arpeggio = [2, 2, 3]
+# broken thirds = [2, -1]
+# broken octaves = [7, -6]
+# broken arpeggio = [4, -2, 5] 
+
+# stateful iterator:
+mutable struct Motif
+    scale::Scale
+    pattern::Vector{Int}
+    current::Pitch
+    i::Int
+end
+
+Motif(scale, pattern) = Motif(scale, pattern, first(iterate(scale)), 1)
+
+function Base.iterate(m::Motif)
+    return_value = m.current
+    current, next = iterate(scale)
+
+    for i in 1:m.pattern[m.i] - 1
+        current, next = iterate(scale, next)
+    end
+
+    m.i += 1
+    if m.i > length(m.pattern)
+        m.i = 1
+    end
+
+    m.current = return_value
+    return return_value, next
+end
+
+function Base.iterate(m::Motif, next)
+
+    return_value = next
+
+    for i in 1:m.pattern[m.i]
+        current, next = iterate(scale, next)
+    end
+
+    m.i += 1
+    if m.i > length(m.pattern)
+        m.i = 1
+    end
+
+    m.current = return_value
+
+    return return_value, next
+end
+
+
+Base.IteratorSize(::Type{Motif}) = Base.IsInfinite()
+Base.IteratorEltype(::Type{Motif}) = Base.HasEltype()
+Base.eltype(::Type{Motif}) = Pitch

test/motifs.jl

@@ -0,0 +1,8 @@
+@testset "Arpeggio" begin
+    scale = Scale(C[4], major_scale)
+    arpeggio_motif = Motif(scale, [2, 2, 3])
+
+    arpeggio = collect(Base.Iterators.take(arpeggio_motif, 6))
+
+    @test arpeggio == Pitch[C[4], E[4], G[4], C[5], E[5], G[5]]
+end