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

[Joachim Breitner]

Hi,

Am Donnerstag, den 16.08.2018, 08:46 +0000 schrieb Simon Peyton Jones
via ghc-steering-committee:
> What would be ambiguous is this and-pattern:
>         Nothing @ pat
> (i.e. with a nullary contructor as the first of p1 at p2).  But that's a
> pretty silly and-pattern so I think we could let this ambiguous case
> resolve as a pattern type application. 

nullary constructors can be synonyms!

   pattern Ascii :: String
   pattern Ascii <- (all isAscii -> True)

and now

   foo (Ascii @ ('X':rest)) = 

is now longer as silly…

>  You could I suppose write
> (Nothing)@pat to get the and-pattern.

Significant parenthesis? Ugh.

But yeah, maybe it is good enough™ to deal with this particular corner.

Cheers,
Joachim



-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/
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