I have just filed this as a bug report. Typed Racket appears to process nested annotations in the wrong order.
Welcome to Racket v5.0.99.5. > (ann (ann 5 Real) Integer) - : Real 5 > (ann (ann 5 Integer) Real) stdin::37: Type Checker: Expected Integer, but got Real in: 5 Carl Eastlund On Wed, Dec 22, 2010 at 3:42 PM, Carl Eastlund <[email protected]> wrote: > I believe your intermediate expression there, the one with two > "ann"otations in it, is a Typed Racket bug. You should definitely not > be able to take something with the type (Listof Symbol) and coerce it > to (List Symbol Symbol). For instance: > >> (: f ((Listof Symbol) -> (List Symbol Symbol))) >> (define (f x) x) > stdin::124: Type Checker: Expected (List Symbol Symbol), but got > (Listof Symbol) in: x > > Carl Eastlund > > On Wed, Dec 22, 2010 at 3:33 PM, Neil Van Dyke <[email protected]> wrote: >> Carl Eastlund wrote at 12/22/2010 03:06 PM: >>> >>> So each time you apply cons, if you don't want a Listof type you have to >>> "convince" it to build something else. Do this by either annotating each >>> step, or binding cons with a simpler type. >>> >> >> Thanks for the explanation. I found that annotating each step in the >> building of lists with "cons" works, but I was a surprised that was >> necessary. >> >> More importantly, I don't understand why the following works without >> signaling an error... >> >>> (list 'a 'b) >> - : (List 'a 'b) >> (a b) >>> (ann (list 'a 'b) (Listof Symbol)) >> - : (Listof Symbol) >> (a b) >>> (ann (ann (list 'a 'b) (Listof Symbol)) (List Symbol Symbol)) >> - : (Listof Symbol) >> (a b) >>> (ann (list 'a 'b) (List Symbol Symbol)) >> - : (List Symbol Symbol) >> (a b) >> >> ...yet the following does get errors when trying to do the same coercion >> from "(Listof Symbol)" to "(List Symbol Symbol)": >> >>> (cons 'a (cons 'b '())) >> - : (Listof (U 'a 'b)) >> (a b) >>> (ann (cons 'a (cons 'b '())) (Listof Symbol)) >> - : (Listof Symbol) >> (a b) >>> (ann (cons 'a (cons 'b '())) (List Symbol Symbol)) >> . . Type Checker: Polymorphic function cons could not be applied to >> arguments: >> Types: a (Listof a) -> (Listof a) >> a b -> (Pairof a b) >> Arguments: 'a (Listof 'b) >> Expected result: (List Symbol Symbol) >> in: (cons (quote a) (cons (quote b) (quote ()))) >>> (ann (ann (cons 'a (cons 'b '())) (Listof Symbol)) (List Symbol Symbol)) >> . . Type Checker: Polymorphic function cons could not be applied to >> arguments: >> Types: a (Listof a) -> (Listof a) >> a b -> (Pairof a b) >> Arguments: 'a (Listof 'b) >> Expected result: (List Symbol Symbol) >> in: (cons (quote a) (cons (quote b) (quote ()))) >> >> >> -- >> http://www.neilvandyke.org/ _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
