The keys() functions extension does not inherit from FilterFunction and define its argument/return types.
We probably need to return a special "Nothing" value that plays nicely with contains and in, then return that if keys() is passed a non-mapping argument.
The
keys()functions extension does not inherit fromFilterFunctionand define its argument/return types.We probably need to return a special "Nothing" value that plays nicely with
containsandin, then return that ifkeys()is passed a non-mapping argument.