[Haskell] Re: View patterns in GHC: Request for feedback

[ajb at spamcop.net]

G'day all.

"Claus Reinke" <claus.reinke at talk21.com> schrieb im Newsbeitrag
news:004a01c7cde1$04b190f0$2e3f8351 at cr3lt...

> >    type Typ
> >
> >    unit :: Typ -> Maybe ()
> >    arrow :: Type -> Maybe (Typ,Typ)
> >    size :: Typ -> Integer
> >    size (unit -> ()) = 1
> >    size (arrow -> (t1,t2)) = size t1 + size t2

The whole point of a view is that you make views that are semantically
useful.

data UsefulView = Unit | Arrow Type Type

usefulView :: Type -> UsefulView

size :: Type -> Integer
size (usefulView -> Unit) = 1
size (usefulView -> Arrow t1 t2) = size t1 + size t2

Cheers,
Andrew Bromage