module Theory exposing (..) import Array exposing (Array) import List.Extra import Maybe.Extra import Misc {-| Notes are the individuals sounds that we use to create music. Think: "do re mi fa so la ti do". Note: Technically a "C-sharp" is also a "D-flat", but I will model accidentals (i.e. sharps and flats) as sharps and represent the ambiguity when I render the underlying state of the application. Note: There are "notes" like A, B, D-flat, and then there are notes like "middle C", also denoted in scientific pitch notation as C4. I'm unsure of what to call each of these, and my application does not model scientific pitch notation yet, so these non-scientific pitch denote values are "notes" for now. -} type Note = C1 | C_sharp1 | D1 | D_sharp1 | E1 | F1 | F_sharp1 | G1 | G_sharp1 | A1 | A_sharp1 | B1 | C2 | C_sharp2 | D2 | D_sharp2 | E2 | F2 | F_sharp2 | G2 | G_sharp2 | A2 | A_sharp2 | B2 | C3 | C_sharp3 | D3 | D_sharp3 | E3 | F3 | F_sharp3 | G3 | G_sharp3 | A3 | A_sharp3 | B3 | C4 | C_sharp4 | D4 | D_sharp4 | E4 | F4 | F_sharp4 | G4 | G_sharp4 | A4 | A_sharp4 | B4 | C5 | C_sharp5 | D5 | D_sharp5 | E5 | F5 | F_sharp5 | G5 | G_sharp5 | A5 | A_sharp5 | B5 | C6 | C_sharp6 | D6 | D_sharp6 | E6 | F6 | F_sharp6 | G6 | G_sharp6 | A6 | A_sharp6 | B6 | C7 | C_sharp7 | D7 | D_sharp7 | E7 | F7 | F_sharp7 | G7 | G_sharp7 | A7 | A_sharp7 | B7 | C8 {-| I alluded to this concept in the Note type's documentation. These are the letters of notes. For instance C2, C3, C4 are all instances of C. -} type NoteClass = C | C_sharp | D | D_sharp | E | F | F_sharp | G | G_sharp | A | A_sharp | B {-| Encode whether you are traversing "up" or "down" intervals -} type StepDirection = Up | Down {-| One can measure the difference between between notes using intervals. -} type Interval = Half | NHalves Int | Whole | MajorThird | MinorThird | PerfectFifth | AugmentedFifth | DiminishedFifth | MajorSeventh | DominantSeventh {-| Add direction to a distance on the piano. -} type alias IntervalVector = { interval : Interval , direction : StepDirection } {-| A bundle of notes which are usually, but not necessarily harmonious. -} type alias Chord = { note : Note , chordType : ChordType , chordInversion : ChordInversion } {-| Many possible chords exist. This type encodes the possibilities. I am tempted to model these in a more "DRY" way, but I worry that this abstraction may cause more problems than it solves. -} type ChordType = Major | Sus2 | Sus4 | Major7 | MajorDominant7 | Minor | MinorMajor7 | MinorDominant7 | Augmented | AugmentedDominant7 | Diminished | DiminishedDominant7 | DiminishedMajor7 {-| On a piano, a triad can be played three ways. As a rule-of-thumb, The number of ways a pianist can play a chord is equal to the number of notes in the chord itself. -} type ChordInversion = Root | First | Second {-| Whether a given note is a white key or a black key. -} type KeyClass = Natural | Accidental {-| Songs are written in one or more keys, which define the notes and therefore chords that harmonize with one another. -} type alias Key = { noteClass : NoteClass , mode : Mode } {-| We create "scales" by enumerating the notes of a given key. These keys are defined by the "tonic" note and the "mode". I thought about including Ionian, Dorian, Phrygian, etc., but in the I would like to avoid over-abstracting this early on, so I'm going to err on the side of overly concrete until I have a better idea of the extent of this project. -} type Mode = BluesMode | MajorMode | MinorMode type alias NoteMetadata = { note : Note , label : String , noteClass : NoteClass , natural : Bool } scaleDegree : Int -> Key -> NoteClass scaleDegree which { noteClass } = case noteClass of _ -> C {-| Returns the Note in the cental octave of the piano for a given NoteClass. For example, C4 -- or "middle C" -- for C. -} noteInCentralOctave : NoteClass -> Note noteInCentralOctave noteClass = case noteClass of C -> C4 C_sharp -> C_sharp4 D -> D4 D_sharp -> D_sharp4 E -> E4 F -> F4 F_sharp -> F_sharp4 G -> G4 G_sharp -> G_sharp4 A -> A4 A_sharp -> A_sharp4 B -> B4 {-| Return the human-readable version of a chord inversion. -} inversionName : ChordInversion -> String inversionName inversion = case inversion of Root -> "Root" First -> "First" Second -> "Second" {-| Return the human-readable version of a chord type. -} chordTypeName : ChordType -> String chordTypeName chordType = case chordType of Major -> "major" Sus2 -> "suspended 2" Sus4 -> "suspended 4" Major7 -> "major 7th" MajorDominant7 -> "major dominant 7th" Minor -> "minor" MinorMajor7 -> "minor major 7th" MinorDominant7 -> "minor dominant 7th" Augmented -> "augmented" AugmentedDominant7 -> "augmented dominant 7th" Diminished -> "diminished" DiminishedDominant7 -> "diminished dominant 7th" DiminishedMajor7 -> "diminished major 7th" {-| Return the note that is one half step away from `note` in the direction, `dir`. In the case of stepping up or down from the end of the piano, this returns a Maybe. -} halfStep : StepDirection -> Note -> Maybe Note halfStep dir note = let everyNote = notesFromRange C2 C8 in case dir of Up -> Misc.comesAfter note everyNote Down -> Misc.comesBefore note everyNote {-| Return a list of steps to take away from the root note to return back to the root note for a given mode. -} intervalsForMode : Mode -> List IntervalVector intervalsForMode mode = let up x = { direction = Up, interval = x } down x = { direction = Down, interval = x } in case mode of MajorMode -> List.map up [ Whole, Whole, Half, Whole, Whole, Whole, Half ] MinorMode -> List.map up [ Whole, Half, Whole, Whole, Half, Whole, Whole ] BluesMode -> List.map up [ MinorThird, Whole, Half, Half, MinorThird ] {-| Return a list of the intervals the comprise a chord. Each interval measures the distance away from the root-note of the chord. -} intervalsForChordType : ChordType -> ChordInversion -> List IntervalVector intervalsForChordType chordType chordInversion = let up x = { direction = Up, interval = x } down x = { direction = Down, interval = x } in case ( chordType, chordInversion ) of -- Major ( Major, Root ) -> [ up MajorThird, up PerfectFifth ] ( Major, First ) -> [ down (NHalves 5), down (NHalves 8) ] ( Major, Second ) -> [ down (NHalves 5), up MajorThird ] -- Sus2 ( Sus2, Root ) -> [ up Whole, up PerfectFifth ] ( Sus2, First ) -> [ down (NHalves 10), down (NHalves 5) ] ( Sus2, Second ) -> [ down (NHalves 5), up Whole ] -- Sus4 ( Sus4, Root ) -> [ up (NHalves 5), up PerfectFifth ] ( Sus4, First ) -> [ down (NHalves 7), down (NHalves 5) ] ( Sus4, Second ) -> [ down (NHalves 5), up (NHalves 5) ] -- Major7 ( Major7, Root ) -> [ up MajorThird, up PerfectFifth, up MajorSeventh ] ( Major7, First ) -> down Half :: intervalsForChordType Major chordInversion ( Major7, Second ) -> down Half :: intervalsForChordType Major chordInversion -- MajorDominant7 ( MajorDominant7, Root ) -> up DominantSeventh :: intervalsForChordType Major chordInversion ( MajorDominant7, First ) -> down Whole :: intervalsForChordType Major chordInversion ( MajorDominant7, Second ) -> down Whole :: intervalsForChordType Major chordInversion -- Minor ( Minor, Root ) -> [ up MinorThird, up PerfectFifth ] ( Minor, First ) -> [ down (NHalves 5), down (NHalves 9) ] ( Minor, Second ) -> [ down (NHalves 5), up MinorThird ] -- MinorMajor7 ( MinorMajor7, Root ) -> up MajorSeventh :: intervalsForChordType Minor chordInversion ( MinorMajor7, First ) -> down Half :: intervalsForChordType Minor chordInversion ( MinorMajor7, Second ) -> down Half :: intervalsForChordType Minor chordInversion -- MinorDominant7 ( MinorDominant7, Root ) -> up DominantSeventh :: intervalsForChordType Minor chordInversion ( MinorDominant7, First ) -> down Whole :: intervalsForChordType Minor chordInversion ( MinorDominant7, Second ) -> down Whole :: intervalsForChordType Minor chordInversion -- Augmented ( Augmented, Root ) -> [ up MajorThird, up AugmentedFifth ] ( Augmented, First ) -> [ down (NHalves 8), down (NHalves 4) ] ( Augmented, Second ) -> [ down (NHalves 4), up MajorThird ] -- AugmentedDominant7 ( AugmentedDominant7, Root ) -> up DominantSeventh :: intervalsForChordType Augmented chordInversion ( AugmentedDominant7, First ) -> down Whole :: intervalsForChordType Augmented chordInversion ( AugmentedDominant7, Second ) -> down Whole :: intervalsForChordType Augmented chordInversion -- Diminished ( Diminished, Root ) -> [ up MinorThird, up DiminishedFifth ] ( Diminished, First ) -> [ down (NHalves 6), down (NHalves 9) ] ( Diminished, Second ) -> [ down (NHalves 6), up MinorThird ] -- DiminishedDominant7 ( DiminishedDominant7, Root ) -> up DominantSeventh :: intervalsForChordType Diminished chordInversion ( DiminishedDominant7, First ) -> down Whole :: intervalsForChordType Diminished chordInversion ( DiminishedDominant7, Second ) -> down Whole :: intervalsForChordType Diminished chordInversion -- DiminishedMajor7 ( DiminishedMajor7, Root ) -> up MajorSeventh :: intervalsForChordType Diminished chordInversion ( DiminishedMajor7, First ) -> down Half :: intervalsForChordType Diminished chordInversion ( DiminishedMajor7, Second ) -> down Half :: intervalsForChordType Diminished chordInversion {-| Return the note in the direction, `dir`, away from `note` `s` intervals -} step : IntervalVector -> Note -> Maybe Note step { direction, interval } note = let doStep int = step { direction = direction, interval = int } in case interval of Half -> halfStep direction note NHalves n -> List.repeat n { direction = direction , interval = Half } |> (\x -> applySteps x note) |> Maybe.andThen (List.reverse >> List.head) Whole -> note |> doStep Half |> Maybe.andThen (doStep Half) MinorThird -> note |> doStep Whole |> Maybe.andThen (doStep Half) MajorThird -> note |> doStep Whole |> Maybe.andThen (doStep Whole) PerfectFifth -> note |> doStep MajorThird |> Maybe.andThen (doStep MinorThird) AugmentedFifth -> note |> doStep PerfectFifth |> Maybe.andThen (doStep Half) DiminishedFifth -> note |> doStep MajorThird |> Maybe.andThen (doStep Whole) MajorSeventh -> note |> doStep PerfectFifth |> Maybe.andThen (doStep MajorThird) DominantSeventh -> note |> doStep PerfectFifth |> Maybe.andThen (doStep MinorThird) {-| Returns a list of all of the notes away from a give `note`. - The 0th element is applied to `note`. - The 1st element is applied to the result of the previous operation. - The 2nd element is applied to the result of the previous operation. - and so on...until all of the `steps` are exhausted. In the case where applying any of the steps would result in running off of either edge of the piano, this function returns a Nothing. -} applySteps : List IntervalVector -> Note -> Maybe (List Note) applySteps steps note = doApplySteps steps note [] |> Maybe.map List.reverse doApplySteps : List IntervalVector -> Note -> List Note -> Maybe (List Note) doApplySteps steps note result = case steps of [] -> Just (note :: result) s :: rest -> case step s note of Just x -> doApplySteps rest x (note :: result) Nothing -> Nothing {-| Return the KeyClass for a given `note`. -} keyClass : Note -> KeyClass keyClass note = if isNatural note then Natural else Accidental {-| Return the NoteClass for a given note. -} classifyNote : Note -> NoteClass classifyNote note = note |> getNoteMetadata |> .noteClass {-| Return a list of the notes that comprise a `chord` -} notesForChord : Chord -> Maybe (List Note) notesForChord { note, chordType, chordInversion } = intervalsForChordType chordType chordInversion |> List.map (\interval -> step interval note) |> Maybe.Extra.combine |> Maybe.map (\notes -> note :: notes) {-| Return the scale for a given `key` -} notesForKey : Key -> List Note notesForKey { noteClass, mode } = let origin = noteInCentralOctave noteClass in case applySteps (intervalsForMode mode) origin of -- We should never hit the Nothing case here. Nothing -> [] Just scale -> scale {-| Return true if `note` is a black key. -} isAccidental : Note -> Bool isAccidental note = note |> isNatural |> not {-| Return true if `note` is a white key. -} isNatural : Note -> Bool isNatural note = note |> getNoteMetadata |> .natural {-| Return a list of all of the notes that we know about. Only return the notes within the range `start` and `end`. -} notesFromRange : Note -> Note -> List Note notesFromRange start end = noteMetadata |> Array.toList |> List.map .note |> List.Extra.dropWhile ((/=) start) |> List.Extra.takeWhile ((/=) end) {-| Return a list of all of the chord inversions about which we know. -} allInversions : List ChordInversion allInversions = [ Root, First, Second ] {-| Return a list of all of the chord types about which we know. -} allChordTypes : List ChordType allChordTypes = [ Major , Sus2 , Sus4 , Major7 , MajorDominant7 , Minor , MinorMajor7 , MinorDominant7 , Augmented , AugmentedDominant7 , Diminished , DiminishedDominant7 , DiminishedMajor7 ] noteMetadata : Array NoteMetadata noteMetadata = Array.fromList [ { note = A1, label = "A1", noteClass = A, natural = True } , { note = A_sharp1, label = "A♯/B♭1", noteClass = A_sharp, natural = False } , { note = B1, label = "B1", noteClass = B, natural = True } , { note = C1, label = "C1", noteClass = C, natural = True } , { note = C_sharp1, label = "C♯/D♭1", noteClass = C_sharp, natural = False } , { note = D1, label = "D1", noteClass = D, natural = True } , { note = D_sharp1, label = "D♯/E♭1", noteClass = D_sharp, natural = False } , { note = E1, label = "E1", noteClass = E, natural = True } , { note = F1, label = "F1", noteClass = F, natural = True } , { note = F_sharp1, label = "F♯/G♭1", noteClass = F_sharp, natural = False } , { note = G1, label = "G1", noteClass = G, natural = True } , { note = G_sharp1, label = "G♯/A♭1", noteClass = G, natural = False } , { note = A2, label = "A2", noteClass = A, natural = True } , { note = A_sharp2, label = "A♯/B♭2", noteClass = A_sharp, natural = False } , { note = B2, label = "B2", noteClass = B, natural = True } , { note = C2, label = "C2", noteClass = C, natural = True } , { note = C_sharp2, label = "C♯/D♭2", noteClass = C_sharp, natural = False } , { note = D2, label = "D2", noteClass = D, natural = True } , { note = D_sharp2, label = "D♯/E♭2", noteClass = D_sharp, natural = False } , { note = E2, label = "E2", noteClass = E, natural = True } , { note = F2, label = "F2", noteClass = F, natural = True } , { note = F_sharp2, label = "F♯/G♭2", noteClass = F_sharp, natural = False } , { note = G2, label = "G2", noteClass = G, natural = True } , { note = G_sharp2, label = "G♯/A♭2", noteClass = G, natural = False } , { note = A3, label = "A3", noteClass = A, natural = True } , { note = A_sharp3, label = "A♯/B♭3", noteClass = A_sharp, natural = False } , { note = B3, label = "B3", noteClass = B, natural = True } , { note = C3, label = "C3", noteClass = C, natural = True } , { note = C_sharp3, label = "C♯/D♭3", noteClass = C_sharp, natural = False } , { note = D3, label = "D3", noteClass = D, natural = True } , { note = D_sharp3, label = "D♯/E♭3", noteClass = D_sharp, natural = False } , { note = E3, label = "E3", noteClass = E, natural = True } , { note = F3, label = "F3", noteClass = F, natural = True } , { note = F_sharp3, label = "F♯/G♭3", noteClass = F_sharp, natural = False } , { note = G3, label = "G3", noteClass = G, natural = True } , { note = G_sharp3, label = "G♯/A♭3", noteClass = G, natural = False } , { note = A4, label = "A4", noteClass = A, natural = True } , { note = A_sharp4, label = "A♯/B♭4", noteClass = A_sharp, natural = False } , { note = B4, label = "B4", noteClass = B, natural = True } , { note = C4, label = "C4", noteClass = C, natural = True } , { note = C_sharp4, label = "C♯/D♭4", noteClass = C_sharp, natural = False } , { note = D4, label = "D4", noteClass = D, natural = True } , { note = D_sharp4, label = "D♯/E♭4", noteClass = D_sharp, natural = False } , { note = E4, label = "E4", noteClass = E, natural = True } , { note = F4, label = "F4", noteClass = F, natural = True } , { note = F_sharp4, label = "F♯/G♭4", noteClass = F_sharp, natural = False } , { note = G4, label = "G4", noteClass = G, natural = True } , { note = G_sharp4, label = "G♯/A♭4", noteClass = G, natural = False } , { note = A5, label = "A5", noteClass = A, natural = True } , { note = A_sharp5, label = "A♯/B♭5", noteClass = A_sharp, natural = False } , { note = B5, label = "B5", noteClass = B, natural = True } , { note = C5, label = "C5", noteClass = C, natural = True } , { note = C_sharp5, label = "C♯/D♭5", noteClass = C_sharp, natural = False } , { note = D5, label = "D5", noteClass = D, natural = True } , { note = D_sharp5, label = "D♯/E♭5", noteClass = D_sharp, natural = False } , { note = E5, label = "E5", noteClass = E, natural = True } , { note = F5, label = "F5", noteClass = F, natural = True } , { note = F_sharp5, label = "F♯/G♭5", noteClass = F_sharp, natural = False } , { note = G5, label = "G5", noteClass = G, natural = True } , { note = G_sharp5, label = "G♯/A♭5", noteClass = G, natural = False } , { note = A6, label = "A6", noteClass = A, natural = True } , { note = A_sharp6, label = "A♯/B♭6", noteClass = A_sharp, natural = False } , { note = B6, label = "B6", noteClass = B, natural = True } , { note = C6, label = "C6", noteClass = C, natural = True } , { note = C_sharp6, label = "C♯/D♭6", noteClass = C_sharp, natural = False } , { note = D6, label = "D6", noteClass = D, natural = True } , { note = D_sharp6, label = "D♯/E♭6", noteClass = D_sharp, natural = False } , { note = E6, label = "E6", noteClass = E, natural = True } , { note = F6, label = "F6", noteClass = F, natural = True } , { note = F_sharp6, label = "F♯/G♭6", noteClass = F_sharp, natural = False } , { note = G6, label = "G6", noteClass = G, natural = True } , { note = G_sharp6, label = "G♯/A♭6", noteClass = G, natural = False } , { note = A7, label = "A7", noteClass = A, natural = True } , { note = A_sharp7, label = "A♯/B♭7", noteClass = A_sharp, natural = False } , { note = B7, label = "B7", noteClass = B, natural = True } , { note = C7, label = "C7", noteClass = C, natural = True } , { note = C_sharp7, label = "C♯/D♭7", noteClass = C_sharp, natural = False } , { note = D7, label = "D7", noteClass = D, natural = True } , { note = D_sharp7, label = "D♯/E♭7", noteClass = D_sharp, natural = False } , { note = E7, label = "E7", noteClass = E, natural = True } , { note = F7, label = "F7", noteClass = F, natural = True } , { note = F_sharp7, label = "F♯/G♭7", noteClass = F_sharp, natural = False } , { note = G7, label = "G7", noteClass = G, natural = True } , { note = G_sharp7, label = "G♯/A♭7", noteClass = G, natural = False } , { note = C8, label = "C8", noteClass = C, natural = True } ] {-| Mapping of note data to commonly needed metadata for that note. -} getNoteMetadata : Note -> NoteMetadata getNoteMetadata note = case Array.get (noteAsNumber note) noteMetadata of Just metadata -> metadata -- This case should never hit, so we just return C1 to appease the -- compiler. Nothing -> getNoteMetadata C1 {-| Return the numeric representation of `note` to ues when comparing two notes. -} noteAsNumber : Note -> Int noteAsNumber note = case note of C1 -> 0 C_sharp1 -> 1 D1 -> 2 D_sharp1 -> 3 E1 -> 4 F1 -> 5 F_sharp1 -> 6 G1 -> 7 G_sharp1 -> 8 A1 -> 9 A_sharp1 -> 10 B1 -> 11 C2 -> 12 C_sharp2 -> 13 D2 -> 14 D_sharp2 -> 15 E2 -> 16 F2 -> 17 F_sharp2 -> 18 G2 -> 19 G_sharp2 -> 20 A2 -> 21 A_sharp2 -> 22 B2 -> 23 C3 -> 24 C_sharp3 -> 25 D3 -> 26 D_sharp3 -> 27 E3 -> 28 F3 -> 29 F_sharp3 -> 30 G3 -> 31 G_sharp3 -> 32 A3 -> 33 A_sharp3 -> 34 B3 -> 35 C4 -> 36 C_sharp4 -> 37 D4 -> 38 D_sharp4 -> 39 E4 -> 40 F4 -> 41 F_sharp4 -> 42 G4 -> 43 G_sharp4 -> 44 A4 -> 45 A_sharp4 -> 46 B4 -> 47 C5 -> 48 C_sharp5 -> 49 D5 -> 50 D_sharp5 -> 51 E5 -> 52 F5 -> 53 F_sharp5 -> 54 G5 -> 55 G_sharp5 -> 56 A5 -> 57 A_sharp5 -> 58 B5 -> 59 C6 -> 60 C_sharp6 -> 61 D6 -> 62 D_sharp6 -> 63 E6 -> 64 F6 -> 65 F_sharp6 -> 66 G6 -> 67 G_sharp6 -> 68 A6 -> 69 A_sharp6 -> 70 B6 -> 71 C7 -> 72 C_sharp7 -> 73 D7 -> 74 D_sharp7 -> 75 E7 -> 76 F7 -> 77 F_sharp7 -> 78 G7 -> 79 G_sharp7 -> 80 A7 -> 81 A_sharp7 -> 82 B7 -> 83 C8 -> 84 {-| Return true if all of the notes that comprise `chord` can be played on a piano whose keys begin at `start` and end at `end`. -} chordWithinRange : Note -> Note -> Chord -> Bool chordWithinRange start end chord = case notesForChord chord of Just notes -> let nums = List.map noteAsNumber notes lo = List.minimum nums |> Maybe.withDefault (noteAsNumber start) hi = List.maximum nums |> Maybe.withDefault (noteAsNumber end) in lo >= noteAsNumber start && hi < noteAsNumber end Nothing -> False {-| Return a list of all of the chords that we know about. -} allNoteClasses : List NoteClass allNoteClasses = [ C , C_sharp , D , D_sharp , E , F , F_sharp , G , G_sharp , A , A_sharp , B ] {-| Return a list of all of the chords that we know about. Only create chords from the range of notes delimited by the range `start` and `end`. -} allChords : { start : Note , end : Note , inversions : List ChordInversion , chordTypes : List ChordType , noteClasses : List NoteClass } -> List Chord allChords { start, end, inversions, chordTypes, noteClasses } = let notes = notesFromRange start end |> List.filter (\note -> List.member (classifyNote note) noteClasses) in notes |> List.Extra.andThen (\note -> chordTypes |> List.Extra.andThen (\chordType -> inversions |> List.Extra.andThen (\inversion -> [ { note = note , chordType = chordType , chordInversion = inversion } ] ) ) ) |> List.filter (chordWithinRange start end) {-| Serialize a human-readable format of `note`. -} viewNote : Note -> String viewNote note = note |> getNoteMetadata |> .label inspectChord : Chord -> String inspectChord { note, chordType, chordInversion } = viewNote note ++ " " ++ chordTypeName chordType ++ " " ++ inversionName chordInversion ++ " position" viewChord : Chord -> String viewChord { note, chordType, chordInversion } = viewNoteClass (classifyNote note) ++ " " ++ chordTypeName chordType ++ " " ++ inversionName chordInversion ++ " position" {-| Serialize a human-readable format of `noteClass`. -} viewNoteClass : NoteClass -> String viewNoteClass noteClass = case noteClass of C -> "C" C_sharp -> "C♯/D♭" D -> "D" D_sharp -> "D♯/E♭" E -> "E" F -> "F" F_sharp -> "F♯/G♭" G -> "G" G_sharp -> "G♯/A♭" A -> "A" A_sharp -> "A♯/B♭" B -> "B"