And

two parts as one

type alias And first second =

( first, second )

Both a first and second part, conveniently represented as a tuple.

Using this type instead of a tuple visually unifies it with all the other types such as List, Maybe, or Result.

This in my opinion reads a tad better, especially as a type argument:

List (Maybe ( String, Int ))

becomes:

List (Maybe (And String Int))

change

firstMap : (first -> firstMapped) -> And first second -> And firstMapped second

Change the first part based on its current value

(second -> secondMapped)

-> And first second

-> And first secondMapped

Change the second part based on its current value