Then you should produce 'some canonical representation for database
entries suited for comparison', like Stefan mentioned. For example:
> data Entry = forall a. (DatabaseEntry a) => Entry a
>
> instance DatabaseEntry Entry where
> entryLabel (Entry e) = entryLabel e
> formatEntry (Entry e) = formatEntry e
> compareEntries (Entry x) (Entry y) = compare (entryLabel x)
(entryLabel y)
Gerrit
Max Vasin wrote:
"Geest," == Geest, G van den <[EMAIL PROTECTED]> writes:
Geest,> I suppose you want to define compareEntries like this:
compareEntries (Entry x) (Entry y) = compareEntries x y
Geest,> An option is to just implement it the following way
Geest,> (Haskell98!):
class DatabaseEntry e where entryLabel :: e -> String formatEntry
:: e -> String compareEntries :: e -> e -> Ordering
data Entry a = Entry a
No. I don't want that. The database parsing function returns
Map.Map String Entry but entries can of different types (and
these type vary over styles).
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
