Sure, it can certainly be done:
class CombineLines a b where
(++) :: a -> b -> Lines
instance CombineLines Line Line where { ... }
instance CombineLines Line Lines where { ... }
instance CombineLines Lines Line where { ... }
instance CombineLines Lines Lines where { ... }
Of course, whether or not such a class is an especially useful thing is
another matter entirely. Other encodings might be more helpful in
practice. Perhaps something like this is closer to what you really want:
class ToLines a where
toLines :: a -> Lines
instance ToLines Line where
toLines = lineToLines
instance ToLines Lines where
toLines = id
(++) :: (ToLines a, ToLines b) => a -> b -> Lines
x ++ y = toLines x `addLines` toLines y
Or perhaps none of these are really all that helpful in practice, and
the overloading isn’t really worth it.
> On Jun 12, 2018, at 22:58, Hilco Wijbenga <hilco.wijbenga@gmail.com> wrote:
>
> Hi all,
>
> Given definitions of Line and Lines is it possible to define a type
> class (or maybe multiple type classes) that would allow for the
> following:
>
> (++) :: Line -> Line -> Lines
> (++) :: Line -> Lines -> Lines
> (++) :: Lines -> Line -> Lines
> (++) :: Lines -> Lines -> Lines
>
> I.e. is there a way to overload (++) such that it supports each of
> these 4 combinations? (Let's ignore that (++) already exists for the
> moment.)
>
> Cheers,
> Hilco
_______________________________________________
Haskell-Cafe mailing list
To (un)subscribe, modify options or view archives go to:
http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
Only members subscribed via the mailman list are allowed to post.