[plt-scheme] typed scheme intro

What type annotations did you put, exactly? I tried changing the
result of mag to Number and otherwise leaving it as is (from the docs)
and I get this:

Welcome to DrScheme, version 4.2.5.6-svn8apr2010 [3m].
Language: typed/scheme; memory limit: 512 MB.
. Type Checker: No function domains matched in function application:
Domains: Exact-Nonnegative-Integer
         Number
Arguments: Number Number
 in: (sqrt (sqr (pt-x p)) (sqr (pt-y p)))


Robby

On Thu, Apr 8, 2010 at 3:11 PM, Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
> Those are both bugs.  The return type of `mag' should be `Number', as
> the untyped version indicates.  I've fixed this in SVN.
>
> sam th
>
> On Thu, Apr 8, 2010 at 3:41 PM, Danny Yoo <dyoo at cs.wpi.edu> wrote:
>> I'm trying to run the mag program described in:
>>
>>    http://docs.plt-scheme.org/ts-guide/quick.html
>>
>> but it doesn't look quite right: the addition of the squared
>> components appears to be missing.
>>
>> Furthermore, when I do change it to:
>>
>> (: mag (pt -> Real))
>> (define (mag p)
>>  (sqrt (+ (sqr (pt-x p))
>>           (sqr (pt-y p)))))
>>
>> I get a type error because I can't convince the type checker that the
>> result of the addition will be a positive real.  I worked around by
>> doing:
>>
>> (: mag (pt -> Real))
>> (define (mag p)
>>  (real-part (sqrt (+ (sqr (pt-x p))
>>                           (sqr (pt-y p))))))
>>
>>
>> Am I missing something?
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>>
>
>
>
> --
> sam th
> samth at ccs.neu.edu
> _________________________________________________
>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>