Re: Misleading strictness annotations in Data.List.NonEmpty

8 Jan 2021


      Yeah, the more I think about it, the more I like your stricter (<|). I
don't see any really useful laziness to add to groupBy1. What were you
thinking of?

On Fri, Jan 8, 2021 at 2:27 PM Keith  wrote:
...
There are a couple other ones that I'm less sure about.
cons:
a <| ~(b :| bs) = a :| b : bs
Unsugared this is
a <| bs = a :|
(case bs of b :| _ -> b ) :
case bs of _ :| bs -> bs
Would this make more sense?
a <| bs = a :| case bs of b :| bs' -> b : bs'
Then
cons x undefined = x :| undefined
not
x :| undefined : undefined
groupBy1 matches strictly, could be lazy. (Is this a performance issue or an oversight?)
—
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On January 8, 2021 6:36:58 PM UTC, Keith  wrote:
...
Thanks, will do.
On January 8, 2021 5:07:25 PM UTC, David Feuer  wrote:
...
The first one. Neither twiddles nor bangs are useful or add clarity.
On Fri, Jan 8, 2021, 11:53 AM Keith  wrote:
...
Currently:
head ~(a :| _) = a
 tail ~(_ :| as) = as
But head and tail are both strict. At best the '~'s have no effect.
Should I open a PR to change it to
head (a :| _) = a
 tail (_ :| as) = as
or maybe even more clearly
head !(a :l _) = a
 tail !(_ :| as) = as
?
 --Keith
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Good to know! Wasn't aware that that was in the works.
And sorry for accidentally threading this onto something unrelated.
-- Keith
Sent from my phone with K-9 Mail.
On January 8, 2021 5:13:31 PM UTC, Henning Thielemann  wrote:
...
On Fri, 8 Jan 2021, Keith wrote:
...
Currently:
head ~(a :| _) = a
tail ~(_ :| as) = as
But head and tail are both strict. At best the '~'s have no effect.
Should I open a PR to change it to
head (a :| _) = a
tail (_ :| as) = as
or maybe even more clearly
head !(a :l _) = a
tail !(_ :| as) = as
?
The last one would trigger the "redundant bang pattern" warning that is
going to be implemented/released:
    https://gitlab.haskell.org/ghc/ghc/issues/17340
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