On Fri, Mar 30, 2012 at 16:56, Roelof Wobben <r.wob...@home.nl> wrote: > Op 30-3-2012 12:17, Pierpaolo Bernardi schreef: > >> On Fri, Mar 30, 2012 at 11:53, Roelof Wobben<r.wob...@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.wob...@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. > > Are you sure ?
Yes. > 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. You must pay more attention to small details. What is the p in (posn-y p)? Isn't an argument missing in (posn-x)? What is the u in (ufo-loc u) (that's the variable that DrRacket says it doesn't know). P. ____________________ Racket Users list: http://lists.racket-lang.org/users
