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. Mostly I'm ripping
off HStringTemplate for the fun of it.
{-# OPTIONS -fglasgow-exts #-}
module Control.WebWidget where
import Data.Monoid
import Data.String
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
toHtml (Element name attrs children) =
mconcat [
fromString "<",
name,
mconcat $ map toHtml attrs,
fromString ">",
mconcat $ map toHtml children,
fromString "</",
name,
fromString ">" ]
toHtml (Text s) = s
instance (Monoid s, IsString s) => HTML (Attr s) s where
toHtml (Attr key value) =
mconcat [
fromString " '",
key,
fromString "'='",
value,
fromString "' " ]
--
Darrin
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