Basically, rather than storing the attributes as given, you should store the resultant properties of a chord with these attributes. One simple (but not really nice, musically) solution would be, storing only the final pitches:
newtype Pitch = Pitch {midiNote :: Int}
a, as, bb, b, bs, c, cs, db, d, ds, eb, e, es, f, fs, gb, g, gs, ab :: Pitch
[ a, as,bb, b,bs, c,cs,db, d,ds,eb, e,es, f,fs,gb, g,gs,ab] = map Pitch
[55,56,56,57,58,58,59,59,60,61,61,62,63,63,64,64,65,66,66]
type Chord = [Pitch]
minor :: Pitch -> Chord
minor (Pitch fund) = map (Pitch . (fund+)) [0, 3, 7]
seventh :: Pitch -> Chord
seventh (Pitch fund) = map (Pitch . (fund+)) [0, 4, 7, 10]
spread :: Chord -> Chord
spread = sort
. zipWith (\octShift (Pitch note) -> Pitch $ note + 12 * octShift) $ cycle [0,1]
To be used as e.g.
chords :: [Chord]
chords = [ minor e, seventh d, minor e, minor a, seventh b, spread $ minor e ]
A more sophisticated approach might actually store the information about a chord in a more musically meaningful way:
data Chord = Chord { fundamental :: Pitch
, gender :: Maybe ChordGender
, ExtraNotes :: [AddNote]
, OctaveShifts :: [Int]
}
data ChordGender = Major | Minor
data AddNote = AddNote { roughInterval :: Int, intervalIsMajor :: Bool }
major :: Pitch -> Chord
major fund = Chord fund (Just Major) [] []
sus4 :: Pitch -> Chord
sus4 fund = Chord fund Nothing [AddNote 4 False] []
spread :: Chord -> Chord
spread ch@(Chord _ _ _ shifts)
= ch{shifts = cycle [0,1]}
This can be used in much the same way, but is more versatile.
If you don't like giving the attributes as prefix functions, you can do as the diagrams package, with
infixl 8 #
(#) :: a -> (a -> b) -> b
(#) = flip ($)
to write
chords = [ c # major
, g # sus4
, g # major
, a # minor
, f # major # spread
, g # sus4 # spread
, g # major # spread
, c # major # spread
]