clamp function in base

[Jon Purdy]

I’m also strongly for ‘clamp :: (Ord a) => (a, a) -> a -> a’.

Even if we don’t resolve it now, I do want to mention that, in discussing
this with some acquaintances recently, we agreed that one-sided clamps
likely warrant a home in ‘Data.Ord’ as well:

atLeast :: (Ord a) => a -> a -> a
atLeast = max
{-# INLINE atLeast #-}

atMost :: (Ord a) => a -> a -> a
atMost = min
{-# INLINE atMost #-}

clamp :: (Ord a) => (a, a) -> a -> a
clamp (lower, upper) = atLeast lower . atMost upper

While their implementations are identical to ‘max’ and ‘min’, semantically
they privilege their arguments differently, serving as documentation of
intent in code like ‘nonnegative = fmap (atLeast 0)’. The hope is that this
may help reduce bugs caused by the common error of mixing up ‘min’ and
‘max’, owing to the unfortunate false friendship between “at least/most”
and “the least/most”.


On Sun, Aug 16, 2020 at 2:43 AM Henning Thielemann <
lemming at henning-thielemann.de> wrote:

>
> On Fri, 14 Aug 2020, Sandy Maguire wrote:
>
> > It seems to me that base is missing the very standard function `clamp ::
> Ord a => a -> a -> a -> a`:
> >
> > ```haskell
> > clamp :: Ord a => a -> a -> a -> a
> > clamp low high = min high .max low
> > ```
>
>
>
> https://hackage.haskell.org/package/utility-ht-0.0.15/docs/Data-Ord-HT.html#v:limit
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