Passing ((-) x) as function to map functions is not intuitive

[kuon]

I noticed that if we do:

desaturatedColor =
    Color.red
    |> mapSaturation ((-) 0.3)

We end up with a color with saturation -0.7 instead of 0.7.

I think being able to pass ((-) x) is good. One workaround would be to chain the passed function with abs, it wouldn't break (*), (+) and always as generating negative makes no real sense (it would change the behavior of (+) -0.5 if the value is less than 0.5 but is it an issue?).

[mdgriffith]

Interesting, yeah that isn't intuitive.

One potential problem with using abs is with something like:

--existing value of 0.3
 mapSaturation ((-) 0.6)
-- results in 0.3, though it should probably result in 0.

Maybe just having a note in the docs to write the full lambda like:

mapSaturation (\x -> x - 0.6)

[kuon]

Yeah I guess, while abs somehow make it intuitive, it has too many drawbacks.

We could suggest the full lambda and also something like:

sub a b =
    b - a

mapSaturation (sub 0.6)

I dunno if any operator makes sense (maybe something like -: instead of sub, but in the end sub is shorter than (-:) so...).

But I guess pointing the issue clearly in the doc and provide the example should be enough.

[kuon]

Do you want a PR with doc update for this? So we can close that one:)