As Any is supertype of all values, what is the equivalent type for function types? (Any -> Any) does not work because of the contra-variant requirement of the argument. (: f ((Any -> Any) -> True)) (define (f g) #t) (f (lambda (x) x) #t) ;; works (f (lambda: ([x : Integer]) #f)) ;; does not work The error is: Type Checker: Expected (Any -> Any), but got (Integer -> Any) in: (lambda: ((x : Integer)) #f) If I understand it correctly, the type I'm looking for is (Bottom -> Any), which satisfies the contra-variant and variant requirements for function subtyping. However, the Bottom type doesn't seem to exist (at least at the user-level, because I remember seeing some error messages that mentioned Top and Bottom). Thanks -- Ismael