[Haskell] Re: Type synonyms in the instance head
ashley at semantic.org
Thu Feb 2 15:53:15 EST 2006
Mads Lindstrøm wrote:
> "You cannot, for example, write:
> type P a = [[a]]
> instance Monad P where ...
> This design decision is independent of all the others, and easily
> reversed, but it makes sense to me."
It's not clear to me how this can be reversed. Wouldn't reversing this
mean introducing "type lambda", and doesn't that raise all kinds of
nasty issues (like having to type-annotate function applications)?
> If I have:
> data LongAndUglyName a = ...
> type ShortAndTellingName a = LongAndUglyName a
> It seems to make sensible to:
> instance Foo ShortAndTellingName
You can do this instead:
type ShortAndTellingName = LongAndUglyName
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