Work around this with explicit let or other intermediate bindings: Welcome to Racket v5.0.99.5. > (let: ([x : Integer 5]) (ann x Real)) - : Real 5 > (let: ([x : Real 5]) (ann x Integer)) stdin::64: Type Checker: Expected Integer, but got Real in: x
Carl Eastlund On Wed, Dec 22, 2010 at 3:54 PM, Carl Eastlund <[email protected]> wrote: > 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
