On Mon, Nov 28, 2011 at 11:05 AM, Ismael Figueroa Palet <[email protected]> wrote: > Now my example typechecks, but effectively I can't do anything with the > function :-( so it is very unpractical
There's no way to have a type that accepts all functions, and also allows you to apply them to particular arguments. What if that function wasn't prepared to accept that argument? What should happen then? > (: f ((Nothing -> Any) -> True)) > (define (f g) #t) > (f (lambda: ([x : Integer]) #t)) > > is there any way to make the typechecker happy, but being able to apply > functions? > > For me, it would be something like: > > (: f ((Bottom -> True) -> True)) > (define (f g) (g 1)) > (f (lambda: ([x : Integer]) #t)) If this program type checked, then you could do this: (f (lambda: ([x : String]) (string-append "a" x))) and then you'd get a runtime error from `string-append'. Those kind of runtime errors are exactly what Typed Racket rules out. > ?? or any other workaround? > should I instead use an untyped module? It really depends on what you're trying to do. What would you want to happen in the case of `string-append'? Once you know what can happen then, it's easier to figure out the right solution. > 2011/11/28 Sam Tobin-Hochstadt <[email protected]> >> >> On Mon, Nov 28, 2011 at 10:35 AM, Ismael Figueroa Palet >> <[email protected]> wrote: >> > 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). >> >> You're probably looking for the type `Nothing'. Note that functions >> of type `(Nothing -> T)' are very hard to apply, though. >> >> -- >> sam th >> [email protected] > > > > -- > Ismael > > -- sam th [email protected] _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
