[Haskell-cafe] Re: HList error with hFoldr
dbueno at gmail.com
Sat Jan 26 14:40:54 EST 2008
On Sat, Jan 26, 2008 at 11:03 AM, Denis Bueno <dbueno at gmail.com> wrote:
> Have I made some sort of simple error, or am I going about this the
> wrong way altogether?
After some fooling around, I came up with something I think makes
sense. Let me know if this is the right/wrong thing. It seems to
work for the examples I've tried so far.
instance (Floating f, MetricSpace e f
,MetricSpace e' f, HZip l l (HCons (e', e') l')
,HFoldr ApplyDistSum Float l' f)
=> MetricSpace (HCons e l) f where
c `dist` c' = sqrt $ hFoldr ApplyDistSum (0::Float) (hZip c c')
Thanks again for your help, oleg.
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