[ghc-steering-committee] Discussion about "Type Application in Patterns" (#126)

[Richard Eisenberg]

So what's the new rule? Is it:

- @ denotes a type application if it is preceded by a non-identifier character and succeeded by a non-whitespace character
- @ denotes an as-pattern if is preceded by an identifier character or succeeded by a whitespace character

This means that `f@ Int` is an as-pattern.

I think the new rule just adds another twist to an already too-complicated plot.

I'm not worried about backward-compat issues here (echoing Joachim's sentiments) but I don't see the advantage to this new spec.

Richard

> On Aug 17, 2018, at 1:27 PM, Joachim Breitner <mail at joachim-breitner.de> wrote:
> 
> Hi,
> 
> Am Freitag, den 17.08.2018, 13:00 -0400 schrieb Eric Seidel:
>> I've always thought of "@Int" as a single syntactic unit, so I'd be happy to disallow spaces between the @ and the type.
> 
> not opposed in principle, but if we go that route, it should also apply
> to type applications in expressions, for consistency. Are we willing to
> potentially break code out there?  (Well, it’s an extension, the fix is
> simple and fully backward-compatible, and most people probably got it
> right in the first place, so maybe breaking is not too bad.)
> 
> Cheers,
> Joachim
> 
> 
> -- 
> Joachim Breitner
>  mail at joachim-breitner.de
>  http://www.joachim-breitner.de/
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