[Agda] recursive \times
Dr. ÉRDI Gergő
gergo at erdi.hu
Fri Apr 12 12:51:37 CEST 2013
Look at Data.List.All in the std lib.
On Apr 12, 2013 6:48 PM, "Serge D. Mechveliani" <mechvel at botik.ru> wrote:
> Please, why the program below is not type-checked?
>
> EachPositive : List Nat -> List (Set _)
> EachPositive xs = map (\ n -> n > 0) xs
>
> f : (ns : List Nat) -> EachPositive ns -> Nat
> f _ _ = 0
>
> -- a contrived example: f takes ns and needs to use a proof for n > 0
> for each n in ns.
>
> If I comment out f, then EachPositive is compiled
> (despite that I expected "List (Set _)" to be wrong).
>
> What should be the intended signature for f ?
>
> I attach to this letter t.agda.zip
>
> -- the variant with ManyProduct -- with applies \times recursively.
>
> 1) Has Standard library something close to ManyProduct ?
> 2) Can the attempt with map (\ n -> n > 0) be improved, or it is just a
> basically wrong idea?
>
> Thank you in advance for explanation,
>
> ------
> Sergei
>
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