2533: Generic functions that take integral arguments should
work the same way as their prelude counterparts
gwern0 at gmail.com
Sat Aug 23 15:46:02 EDT 2008
On 2008.08.23 17:33:55 -0000, kahl at cas.mcmaster.ca scribbled 0.9K characters:
> Neil Mitchell <ndmitchell at gmail.com> wrote:
> > > Hi
> > >
> > >> The Prelude functions drop, take, and splitAt are unfailing (never
> > >> call error). This patch changes the Data.List generic versions to
> > >> behave the same way. At present, they call error on negative
> > >> arguments.
> > >
> > > I had always just assumed that take and genericTake did the same
> > > thing, so had never even realised this problem existed. I'd call this
> > > a bug, that needs fixing.
> > Maybe the bug is in 'drop', 'take' and 'splitAt' and it was intended to
> > fix it in 'generic' variants. Is there a good reason why to ignore
> > negative number arguments? It may hide bugs.
> A similar argument could be made against ``take 5  = ''.
> A different solution would be using Nat or Natural as arguments here ---
> then the conversion introduces an obvious place to check for errors.
I've actually long wondered about this: why don't more functions use Nat where it'd make sense? It can't be because Nat is hard to define - I'd swear I've seen many definitions of Nat (if not dozens when you count all the type-level exercises which include one).
ISSSP SADT NSV Rachel HAMASMOIS & Lindows wire ASPIC clandestine
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