Discussion: lookups in maps

[Ivan Lazar Miljenovic]

I know I've had cases where I didn't have a good default `a` but did have
an `r` (and I wanted to apply a function to the result if there was a value
in the Map anyway).


On mobile; please excuse any tpyos.

On Tue, 9 Jun 2020, 5:49 am Oliver Charles, <ollie at ocharles.org.uk> wrote:

> Could you share why you are more enthusiastic about such a function?
>
> On Mon, 8 Jun 2020, at 8:07 PM, David Feuer wrote:
>
> Discussion has gotten going again about harmonizing between the names
> findWithDefault and lookupDefault in containers and unordered-containers:
>
>     findWithDefault :: Ord k
>       => a -> k -> Map k a -> a
>     lookupDefault :: (Eq k, Hashable k)
>       => a -> k -> HashMap k a -> a
>
> I've been fairly unenthusiastic about adding extra names for this function
> in one package or the other, in large part because I don't like the
> function. I'd much rather have something in the spirit of `either`,
> `maybe`, `bool`, etc.:
>
>     lurkup :: Ord k
>        => r -> (a -> r) -> k -> Map k a -> r
>     lurkup r f k = maybe r f . lookup k
>     lookup k = lurkup Nothing Just k
>
> Unfortunately, I haven't been able to come up with a decent name for this
> function. Can anyone help?
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