Darrin Thompson wrote:
I thought that I should be able to write something like the toHtml function below with pure H98, but when I went to write it I ended up needing fundeps. Is there a way to express this without using any extensions?
The idea was to take a remotely Dom-like tree and flatten it into a string, but not require any particular string type.
data (IsString s, Monoid s) => Dom s = Element s [Attr s] [Dom s] | Text s
data (IsString s, Monoid s) => Attr s = Attr s s
class (Monoid s, IsString s) => HTML d s | d -> s where toHtml :: d -> s
instance (Monoid s, IsString s) => HTML (Dom s) s where
instance (Monoid s, IsString s) => HTML (Attr s) s where
The H98 way is to make a class for type constructors: class HTML d where toHTML :: (Monoid s, IsString s) => d s -> s instance HTML Dom where ... instance HTML Attr where ... Btw, naming the class "HTML" is feels wrong, something like Serialize is probably a better fit. Regards, apfelmus