[racket] ufo structure problem

Op 30-3-2012 12:17, Pierpaolo Bernardi schreef:
> On Fri, Mar 30, 2012 at 11:53, Roelof Wobben<r.wobben at home.nl>  wrote:
>> Op 30-3-2012 9:46, Pierpaolo Bernardi schreef:
>>
>>> Hello Roelof,
>>>
>>> On Fri, Mar 30, 2012 at 09:32, Roelof Wobben<r.wobben at home.nl>    wrote:
>>>
>>>> (define (show-ufo ufo)
>>>>   (place-image BLU (ufo-loc u) MTS))
>>>>
>>>> But still I can't get the show-ufo work.
>>> Check carefully the name of your variables!
>>>
>>> Doesn't DrRacket give you an explicative error message in this case?
>>>
>>> P.
>>>
>> Oke, I will do that.
>>
>> Yes, The error that variable u is not known.
> I didn't want to tease you.  I thought that you would see it if I
> pointed you at it.  8^)
>
> (define (show-ufo ufo)
>     (place-image BLU (ufo-loc u) MTS))
>
> See that the variables ufo and u should actually the same variable.
> So, either you rename u to ufo, or rename ufo to u.
>
> There may be other errors, I have not checked further.
>
> Cheers
> P.
>
>
>
>>
>> Roelof
>>
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Are you sure ?

I thought that the position of the ufo can be find at (posn-y p) and 
(posn-x) because the postition is a struct of Posn.

Roelof