Is there, in Haskell, something similar to sub-guards?

Question

I\'m writing a program on the classification of musical intervals. The conceptual structure is quite complicated and I would represent it as clearly as possible. The first f

Answer 1

I'd recommend to group each nested condition in a function:

interval :: _ -> _ -> (String, String)
interval pt1 pt2
    | gd == 0 = doSomethingA pt1 pt2
    | gd == 1 = doSomethingB pt1 pt2
    | gd == 2 = doSomethingC pt1 pt2
    ...

and then, for example:

doSomethingA :: _ -> _ -> (String, String)
doSomethingA pt1 pt2
    | sd <  (-2) = ("unison",show (abs sd) ++ "d") 
    | sd == (-2) = ("unison","dd")
    | sd == (-1) = ("unison","d")
    | sd == 0    = ("unison","P")
    | sd == 1    = ("unison","A")
    | sd == 2    = ("unison","AA")
    | sd >  2    = ("unison",show sd ++ "A")
    where sd = displacementInSemitonesOfPitches pt1 pt2  

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Alternatively you can use the MultiWayIf language extension:

interval pt1 pt2 =
    if | gd == 0 -> if | sd <  (-2) -> ("unison",show (abs sd) ++ "d") 
                       | sd == (-2) -> ("unison","dd")
                       | sd == (-1) -> ("unison","d")
                       ...
       | gd == 1 -> if | sd <  (-1) -> ("second",show (abs sd) ++ "d")
                       | sd == (-1) -> ("second","dd")
                       | sd == 0    -> ("second","d")
                       ...