[racket] "error: degrees->complex: 360.0"

There's a random-real generator in 
"math/private/utils/flonum-tests.rkt". The generator Typed Racket uses 
is in "tests/typed-racket/random-real.rkt".

I haven't settled on a general-purpose real number generator. For 
flonums I usually write something like this:

#lang racket

(require math/base math/flonum)

(define max-ord (flonum->ordinal +max.0))

(define (random-flonum)
   (define r (random))
   (cond [(< r 0.025)  +nan.0]
         [(< r 0.050)  +inf.0]
         [(< r 0.075)  -inf.0]
         [(< r 0.100)  -0.0]
         [(< r 0.125)  +0.0]
         [else  (ordinal->flonum (random-integer (- max-ord)
                                                 (+ max-ord 1)))]))

Sometimes I have cases for -max.0, -min.0, +min.0 and +max.0 to test 
near-underflow and near-overflow conditions, or a (- (random) 0.5) or 
similar case to test more typical inputs.

Rationals are a trickier because they're unbounded in both size and 
precision. Probabilistically, they're a weird domain: a uniform 
probability distribution over any given interval of rationals doesn't 
exist. You can get around this by using a fixed precision, but what 
would you fix it at?

Neil ⊥

On 05/13/2014 11:46 AM, Robby Findler wrote:
> Okay, then I'll go with this:
>
> (define/contract (angle->proper-range α)
>    (-> real? (between/c 0 360))
>    (let loop ([θ (- α (* 360 (floor (/ α 360))))])
>      (cond [(negative? θ) (+ θ 360)]
>            [(>= θ 360)    (- θ 360)]
>            [else θ])))
>
> Can you point me to your random real number generator, btw?
>
> Robby
>
>
> On Tue, May 13, 2014 at 9:06 AM, Neil Toronto <neil.toronto at gmail.com> wrote:
>> I can't get it to take more than on iteration, either. It's there in case I
>> missed something. :)
>>
>> Neil ⊥
>>
>>
>> On 05/13/2014 05:59 AM, Robby Findler wrote:
>>>
>>> Thanks, Neil!
>>>
>>> Why is the loop needed? I can't seem to get it to take more than one
>>> iteration.
>>>
>>> Robby
>>>
>>> On Mon, May 12, 2014 at 11:24 PM, Neil Toronto <neil.toronto at gmail.com>
>>> wrote:
>>>>
>>>> He went with exact rationals. Here's another option, which preserves
>>>> inexactness:
>>>>
>>>>       (define (angle->proper-range α)
>>>>         (let loop ([θ  (- α (* 360 (floor (/ α 360))))])
>>>>           (cond [(negative? θ)  (loop (+ θ 360))]
>>>>                 [(>= θ 360)     (loop (- θ 360))]
>>>>                 [else  θ])))
>>>>
>>>> Its accuracy drops off outside of about [-1e16,1e16].
>>>>
>>>> The fact that this is hard to get right might be good motivation for an
>>>> `flmodulo` function.
>>>>
>>>> Neil ⊥
>>>>
>>>>
>>>> On 05/12/2014 09:49 PM, Sean Kanaley wrote:
>>>>>
>>>>>
>>>>> Interesting, my code has the same bug then.  I called it modulo/real,
>>>>> used for things like displaying the space ship's rotation to the user or
>>>>> wrapping x coordinates to stay in the world.  Apparently it's going to
>>>>> fail at some point with vector ref out of range.  What was your fix?  I
>>>>> was thinking to just clamp explicitly like mod/real = (max 0 (min
>>>>> the-mod-minus-1 (old-modulo/real x)))
>>>>>
>>>>>
>>>>> On Mon, May 12, 2014 at 11:12 PM, Robby Findler
>>>>> <robby at eecs.northwestern.edu <mailto:robby at eecs.northwestern.edu>>
>>>>> wrote:
>>>>>
>>>>>       Right. Probably there is a better fix, but the essential problem,
>>>>> as I
>>>>>       understand it, is that there are more floating points between 0 and
>>>>> 1
>>>>>       than between any two other integers and the code made the
>>>>> assumption
>>>>>       that that didn't happen....
>>>>>
>>>>>       The basic desire is to turn a real number into a number in [0,360)
>>>>>       such that the result represents the same number in degrees but is
>>>>>       normalized somehow.
>>>>>
>>>>>       Robby
>>>>>
>>>>>       On Mon, May 12, 2014 at 10:06 PM, Danny Yoo <dyoo at hashcollision.org
>>>>>       <mailto:dyoo at hashcollision.org>> wrote:
>>>>>        > Wow.  Floating point really is nasty.  I see how it might have
>>>>>       happened now.
>>>>>        >
>>>>>        > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>>>>        >> -0.0000000000000001
>>>>>        > -1e-16
>>>>>        >> (+ 360 -1e-16)
>>>>>        > 360.0
>>>>>        >>
>>>>>        > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ____________________
>>>>>      Racket Users list:
>>>>>      http://lists.racket-lang.org/users
>>>>>
>>>>
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>>
>>