[Haskell-cafe] Promoting associated data types

[Kosyrev Serge]

I'm sorry, I made a mistake in the type signature of 'prefer' --
CatEntry ought to be CatAssoc:

> prefer ∷ Category c ⇒ c → CatAssoc → CatX c → CatX c

yielding:

> prefer ∷ Category c ⇒ c → CatAssoc → CatX c → CatX c
> prefer cat (CatAssoc xs) defx =
>     case find (\(CatEntry (icat, _)) → cat == icat) xs of
>       Just (CatEntry (icat, x)) → x
>       Nothing                   → defx

..and

> prefer ∷ Category c ⇒ c → CatAssoc → LayoutName c → LayoutName c
> prefer cat (CatAssoc xs) deflayout =
>     case find (\(CatEntry (icat, _)) → cat == icat) xs of
>       Just (CatEntry (icat, lay)) → lay
>       Nothing                     → deflayout

-- 
respectfully,
Косырев Серёга