Interestingly, in Common Lisp, (push event (gethash day days)) does this with zero extra effort, since the default value for fetching from a hashtable is NI

Interestingly, in Common Lisp, (push event (gethash day days)) does this with zero extra effort, since the default value for fetching from a hashtable is NIL. The magic of reasonable defaults... I feel like it's underappreciated sometimes.