[racket] for*/list and Typed Racket
Hi All,
It seems that the problem is in for*/list: itself. For example, the
following code fails to typecheck, but I don't see anything wrong with
it:
#lang typed/racket
(for*/list: ([a : Number '(1 2 3)]
[b : Number '(4 5 6)])
(+ a b))
Any idea of why doesn't typecheck? I'm totally lost now ...
Thanks.
2012/6/25 Adolfo Pérez Álvarez <adolfo.pa at gmail.com>:
> Oh my ... I mis-annotated the code *again* :-(
>
> Here is the corrected definition of colorize:
>
> (: colorize : Map (Listof Color) -> (Listof Solution))
> (define (colorize map colors)
> (for/fold: ([solutions : (Listof Solution) empty-solution]) ([entry
> : Map map])
> (match-let ([(cons region neighbours) entry])
> (for*/list: ([s : Solution solutions]
> [c : Color colors]
> #:when (not (findf (λ: ([rc : (Pair Region Color)])
> (and (memv (car rc) neighbours)
> (eqv? (cdr rc) c)))
> s)) )
> (cons (cons region c) s)))))
>
> 2012/6/25 Adolfo Pérez Álvarez <adolfo.pa at gmail.com>:
>> Thanks a lot for your answer, Sam. It seems I completely missed the
>> for/xxx: forms while looking up the documentation.
>>
>>> One, as the error message said, Typed Racket needed more help in the
>>> form of annotations to check your program. Two, you were using
>>> `for*/list` as if it was `for*/fold`. Unfortunately, the
>>
>> Sorry to inform you that your version doesn't work as expected ;-) I
>> use for*/list to generate 'n' new partial solutions for each one of
>> the 's' generated by the outer for/fold for each color (it's is a
>> quick and dirty solution to the map coloring problem). So the inner
>> for/fold: doesn't do the trick :-).
>>
>> Anyway, I got the type annotations completely wrong ... by mistake I
>> defined a set of solutions as a (Listof (Pair Region Color)) instead
>> of a (Listof (Listof (Pair Region Color))). Also, I should have called
>> "empty-solution" "empty-solutions" or "empty-solution-set" instead.
>>
>> Now I've tried to use for*/list:, annotating the bindings (correctly I
>> hope), but still doesn't work. It fails (again) with the same error
>> message:
>>
>> Type Checker: Error in macro expansion -- insufficient type
>> information to typecheck. please add more type annotations in:
>> (for*/list: ((s : (Listof (Pair Region Color)) solutions) (c : (Listof
>> Color) colors) #:when (not (findf (λ: ((rc : (Pair Region Color)))
>> (and (memv (car rc) neighbours) (eqv? (cdr rc) c))) s))) (cons (cons
>> region c) s))
>>
>> To make things a little clearer I've added a new type "Solution"; now
>> the code looks like this:
>>
>> #lang typed/racket
>>
>> (define-type Region Number)
>> (define-type Color Number)
>> (define-type Solution (Listof (Pair Region Color)))
>>
>> (: empty-solution : (Listof Solution))
>> (define empty-solution '(()))
>>
>> (define-type Map (Listof (Pair Region (List Region))))
>>
>> (: colorize : Map (Listof Color) -> (Listof Solution))
>> (define (colorize map colors)
>> (for/fold: ([solutions : (Listof Solution) empty-solution]) ([entry
>> : Map map])
>> (match-let ([(cons region neighbours) entry])
>> (for*/list: ([s : Solution solutions]
>> [c : (Listof Color) colors]
>> #:when (not (findf (λ: ([rc : (Pair Region Color)])
>> (and (memv (car rc) neighbours)
>> (eqv? (cdr rc) c)))
>> s)) )
>> (cons (cons region c) s)))))
>>
>> And again, thanks a lot for your answer.