Ok, it took me a while to see how to eliminate the apply:
(define-syntax-rule (table (a ...) body)
(for/list : (Listof (Listof Boolean))
([b : (Listof Boolean) (boolean-tuple (length '(a ...)))])
(match-define (list a ...) b)
(append b (list ((λ ([a : Boolean] ...) : Boolean
body) a ...)))))
Dan
On Sat, Jun 11, 2016 at 7:47 AM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu>
wrote:
> The problem here is that you have a fixed-argument function (taking 3
> Boolean arguments) and you're applying it to a list of unknown length. Your
> program knows that this won't be a problem, because `boolean-tuple` always
> produces a list of exactly the right length, but Typed Racket doesn't know
> that.
>
> Sam
>
> On Fri, Jun 10, 2016 at 5:39 PM Daniel Prager <daniel.a.pra...@gmail.com>
> wrote:
>
>> I'm working my way through the 99 Lisp Problems (
>> http://www.ic.unicamp.br/~meidanis/courses/mc336/2006s2/funcional/L-99_Ninety-Nine_Lisp_Problems.html)
>> to improve my proficiency with Typed Racket.
>>
>> While sometimes the discipline of the types helps me catch mistakes,
>> quite often I find myself wrestling to get through the type-check.
>>
>> My tactics to get things working include: dropping back to Racket to make
>> the program work first, switching between for/... and recursive forms,
>> widening the type (e.g. from Natural to Integer), and using cast.
>>
>> I'll post some examples of where I've struggled (or am struggling). First
>> example below.
>>
>> Tips and strategies gratefully accepted!
>>
>> Dan
>>
>>
>> The first example writes out truth tables for a boolean expression with
>> an arbitrary number of parameters.
>>
>> E.g.
>>
>> > (table (a b c) (equal? (and a (or b c))
>> (or (and a b)
>> (and a c))))
>> ; a b c result
>> ;
>> '((#t #t #t #t)
>> (#t #t #f #t)
>> (#t #f #t #t)
>> (#t #f #f #t)
>> (#f #t #t #t)
>> (#f #t #f #t)
>> (#f #f #t #t)
>> (#f #f #f #t))
>>
>>
>> Works in Racket:
>>
>> #lang racket
>>
>> ;P48 (**) Truth tables for logical expressions (3).
>>
>> (define (boolean-tuple n)
>> (if (= n 1)
>> '((#t) (#f))
>> (for*/list
>> ([a '(#t #f)] [t (boolean-tuple (sub1 n))])
>> (cons a t))))
>>
>> (define-syntax-rule (table (a ...) body)
>> (for/list
>> ([b (boolean-tuple (length '(a ...)))])
>> (append b (list (apply (λ (a ...)
>> body)
>> b)))))
>>
>>
>> Can't get past type-check in TR:
>>
>> #lang typed/racket
>>
>>
>> (define (boolean-tuple [n : Integer]) : (Listof (Listof Boolean))
>> (if (= n 1)
>> '((#t) (#f))
>> (for*/list : (Listof (Listof Boolean))
>> ([a '(#t #f)] [t (boolean-tuple (sub1 n))])
>> (cons a t))))
>>
>> (define-syntax-rule (table (a ...) body)
>> (for/list : (Listof (Listof Boolean))
>> ([b : (Listof Boolean) (boolean-tuple (length '(a ...)))])
>> (append b (list (apply (λ ([a : Boolean] ...) : Boolean
>> body)
>> b)))))
>>
>> Type Checker: Bad arguments to function in `apply':
>> Domain: Boolean Boolean Boolean
>> Arguments: (Listof Boolean) *
>> in: (apply (λ ((a : Boolean) ...) : Boolean body) b)
>>
>> --
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>
--
*Daniel Prager*
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