It's wrong that it's "improper" to use the term "variable" for Haskell variables, since it is an established usage. This usage of "variable" occurs in the very

It's wrong that it's "improper" to use the term "variable" for Haskell variables, since it is an established usage. This usage of "variable" occurs in the very first paragraph of Church's first paper on lambda calculus from 1931 in the motivation for the whole project!