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

[Noon van der Silk]

Yes I agree with Tom; it's at least a bit unexpected because unlike with
records, there is (if I understand well) nothing I can write inside the {}
that would actually be valid for that type.

On Thu, 30 Nov 2023 at 14:06, Tom Ellis <
tom-lists-haskell-cafe-2023 at jaguarpaw.co.uk> wrote:

> 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?
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-- 
Noon van der Silk, ن

http://silky.github.io/

"My programming language is kindness."
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