Get a chord's type:

chordType (dominantSeventh PitchClass.a) == ChordType.dominantSeventh

Get a chord's root:

root (dominantSeventh PitchClass.a) == PitchClass.a

Determine whether a chord contains a given pitch class:

containsPitchClass PitchClass.cSharp (major PitchClass.a) == True

Detect chords that contain the given pitch classes:

detect
    [ ChordType.majorSix
    , ChordType.minorSeventh
    ]
    [ PitchClass.a
    , PitchClass.c
    , PitchClass.e
    , PitchClass.g
    ]
    == [ minorSeventh PitchClass.a
       , majorSix PitchClass.c
       ]

Passing in a list of chord types to detect is required, since there exists no exhaustive list of valid chords in tonal music.

Get the pitch classes in a chord:

toPitchClasses (major PitchClass.a)
    == [ PitchClass.a
       , PitchClass.cSharp
       , PitchClass.e
       ]

Note: for converting a chord to pitches, I recommend looking at the functions in the Voicing chords section below.

Get the chord symbol for a chord:

toString (dominantNinth PitchClass.a) == "A9"

Looking for more flexibility? Look at ChordType.classify.

Create a chord from a custom chord type. For use with ChordType.custom:

myCustomChordType =
    ChordType.custom
        |> ChordType.withMinorThird
        |> ChordType.withDiminishedFifth
        |> ChordType.withMinorSeventh


myCustomChord =
    |> custom PitchClass.c myCustomChordType


-- Equivalent to `halfDiminishedSeventh PitchClass.c`

You can also use custom to construct a chord from a chord type, in cases where the chord type may vary:

custom PitchClass.c ChordType.majorSeventh
    == Chord.majorSeventh PitchClass.c