[Haskell-cafe] Strange quirk with {} syntax?

[Tom Ellis]

It was unexpected to me because A1 and A2 were not defined as record
constructors.  (Since I discovered it I now use it regularly; it's
very nice.)

On Thu, Nov 30, 2023 at 02:58:43PM +0100, David Kraeutmann wrote:
> Yes. You're just using record pattern match with no records. Why would it be
> unexpected?
> 
> On 30.11.2023 14:46, Noon van der Silk wrote:
> > Sometimes I have a type like:
> > 
> >     data A = A1 Int | A2 Int Int
> > 
> > Then if I want to do pattern matching and ignore the parameters I do:
> > 
> >     f (A1 _) = ..
> >     f (A2 _ _) = ...
> > 
> > But that's annoying; I need to remember how many parameters each one has!
> > 
> > Yesterday I learned I can just do this:
> > 
> >     f A1 {} = ...
> >     f A2 {} = ...
> > 
> > And GHC is happy.
> > 
> > Is this expected? Am I the last to learn about this trick?