Haskell Typeclass for Tuples -


i playing around typeclasses , made this:

class firstable f   fst :: f ->  class secondable f   snd :: f ->

i tried add implementation (,) , realized do:

instance secondable ((,) a)   snd (x,y) = y

i'm pretty sure works because secondable should have kind (* -> *) ((,) a) has type, however, don't know how implement firstable ((,) * a) * bound variable, in interpretation trying equivalent of:

instance firstable (flip (,) a) ...

is there way in haskell? preferably without extensions?

thanks!

a version worse parametricity guarantees can had mptcs , fundeps or typefamilies.

type family fst p type instance fst (a,b) = type instance fst (a,b,c) =

...

class first p    fst :: p -> fst p  instance fst (a,b)    fst (a,_) =  instance fst (a,b,c)    fst (a,_,_) =

...

but ultimately, you'll need use extensions.


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