[Haskell-cafe] Re: Rewrite class with fundeps in pure h98?
s.clover at gmail.com
Tue Jun 3 15:02:49 EDT 2008
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
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
>> 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.
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