I am trying to get a feel for the draw library in Scheme, but I've already had a problem.
(define defaultpos (make-posn 400 400))
(start 800 800)
(draw-circle defaultpos 10 'green)
In theory, this should open up a new window with a green circle in the middle. Instead, I get this error message:
draw-circle: expects a posn as first argument, given #<posn>
I've tried just making a list with two elements in it as the position, but that obviously doesn't work. Next, I checked whether the defaultpos was actually a posn struct, which it is.
(posn? defaultpos)
> #t
Can anybody help me?
Are you sure you're using the right language and imports? Set your language to "beginning student" and try this, it works for me:
(require htdp/draw)
(define defaultpos (make-posn 400 400))
(start 800 800)
(draw-circle defaultpos 10 'green)