 tree to its generic representaion. This function is
-- inverse of 'toBin'. Constructor for unit tree is called @"Leaf"@, for
-- composite tree -- @"Bin"@.
fromBin ∷ Bin a → BinG a
fromBin Leaf        = LEFT  . CONS "Leaf" $ UNIT
fromBin (Bin l x r) = RIG
fromBin ∷ Bin a → BinG a
fromBin Leaf        = LEFT  . CONS "Leaf" $ UNIT
fromBin Leaf        = LEFT  . CONS "Leaf" $ UNIT