| pattern Ascii :: String
| pattern Ascii <- (all isAscii -> True)
|
| and now
|
| foo (Ascii @ ('X':rest)) =
|
| is now longer as silly…
That’s a good example. It's easy to work around:
pattern And p q = p@q
foo (Ascii `And` ('X' : rest)) = ..
The proposal draw attention to whether ( (K) @type ) is or is not a legal pattern type application. I think currently it is not. So using "significant" parentheses would be another workaround.
Neither workaround is truly satisfactory, but I think the goodness of type applications in patterns (which we know we want) is more important than truly uniform and-patterns (which no one is asking for, yet).
Simon
| -----Original Message-----
| From: ghc-steering-committee
| On Behalf Of Joachim Breitner
| Sent: 16 August 2018 23:02
| To: ghc-steering-committee@haskell.org
| Subject: Re: [ghc-steering-committee] Discussion about "Type Application
| in Patterns" (#126)
|
| 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@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@joachim-breitner.de
|
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