TIL that memoize doesn’t memoize when the memoized function returns nil.

Might be worth creating an issue for that behavior, if there isn't already one.

Is anyone using lipsy? When I am typing and I want to create a function, when I press [ it jumps to the beginning of the expression

I will report that memoize issue. Looks like I’m supposed to do that at https://debbugs.gnu.org/ , but that seems to be down.