`double?` predicate

[shellbro]

There is a new predicate double? added to Clojure 1.9. I just found out about it and it might be a good idea to add it to Clojure cheat sheet for completeness. The right place would be Primitives > Numbers > Test list of predicates.

[jafingerhut]

double? and several other new-in-Clojure-1.9 predicate functions were added to the new "Spec" section of the cheat sheet shortly after Clojure 1.9 was released, but I agree it makes sense to add them to the Primitives > Numbers > Test section of the cheatsheet as well.

Added with this commit to this repository, and also now published at the usual place at http://jafingerhut.github.io

It should make its way to the cheatsheet on clojure.org in time. Not sure of time frame there.