This was how it was originally done in HStringTemplate, as I recall.
The mptcs were introduced in order to maintain lookup-maps of the
correct type, and particularly to allow embedding of templates within
one another. There may have been some other corner-cases involved as
well. However, unless you run into them, the H98 way is certainly
cleaner.
--Sterl
On Jun 3, 2008, at 1:17 PM, apfelmus wrote:
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
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