[Haskell-beginners] MaximumBy

[Ut Primum]

Hi,
if it is ok for you to work only with lists (not generic foldables), you
could write it this way:

maximumBy cmp [x] = x
maximumBy cmp (x:y:xs) = if (cmp x y)==GT then maximumBy cmp (x:xs) else
maximumBy cmp (y:xs)

the signature is
maximumBy :: (a -> a -> Ordering) -> [a] -> a

Ut



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Il giorno ven 22 mag 2020 alle ore 20:53 Alexander Chen <
alexander at chenjia.nl> ha scritto:

> Hi,
>
> maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
>
> its in the Data.List
>
> May 22, 2020 8:33:33 PM CEST "Daniel van de Ghinste (Lord_Luvat)" <
> danielvandeghinste at gmail.com> wrote:
>
> Hi,
>
> Maybe I’m on a different version, but I don’t see a function called
> maximumBy in my base Prelude. Can you give us a type signature for the
> function? If you’re not sure how to do that just type:
> Prelude> :t maximumBy
> In your ghci interpreter and it should return the type signature of
> whatever you have after ‘:t ‘ (this works for compound expressions too if
> you put them in brackets)
>
> Perhaps maximumBy is what you’re meant to call your rewrite of the
> existing function I see called ‘maximum’ (seems to do the same thing). Let
> me know if thats the case and I can explain how it works.
>
>
> Best regards,
> Daniel van de Ghinste
>
> On 22 May 2020, at 20:20, Alexander Chen <alexander at chenjia.nl> wrote:
>
> Hi,
>
> I want to re-write a function maximumBy (its an assignment).
>
> However, I don't get how it works.
>
> >maximumBy compare [1,53,9001, 10]
> 9001
>
> but what does it actually do to get there?
>
> thanks in advance.
>
> best,
>
>
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