[racket] use plot as render in universe

Thanks for the assurance. It helped me to focus on my
world->list-of-vectors It turns out it did not return enough vectors (at
least 2, I think) for initial-world.




On Sun, Aug 11, 2013 at 12:34 PM, Matthias Felleisen
<matthias at ccs.neu.edu>wrote:

>
> On Aug 10, 2013, at 7:04 PM, J G Cho wrote:
>
> I get an error (somewhat expectedly) when I try
>
>   (big-bang init
>             (on-tick random-walk 1)
>             ;(on-key door-actions)
>             (to-draw plot-render)
>             ))
>
> where plot-render is defined as
>
> (define (plot-render world)
>   (p:plot (p:lines
>          (world->list-of-vectors world)
>          #:color 6 #:label "Random walk")))
>
> with the following at the top
>
> (require (prefix-in p: plot))
>
> The error msg is
>
> plot: could not determine sensible plot bounds; got x ∈ [0,0], y ∈ [1,1]
>
> Is there way to let plot know of the context? Or pass a context to plot
> and extract the pixels and hand it over to via some proc in 2htdp/image? Or
> maybe there is a simple way?
>
>
>
> This works like a charm for me:
>
> #lang racket
>
> (require (prefix-in p: plot) 2htdp/universe)
>
> (define (plot-render world)
>   (p:plot (p:lines (world->list-of-vectors world)
>            #:color 6 #:label "Random walk")))
>
> (define (world->list-of-vectors world)
>   `(#(1 3) #(2 -2) #(4 3)))
>
> (define (random-walk world)
>   'more-dummy)
>
> (big-bang 'dummy ; init
>           (on-tick random-walk 1)
>           (to-draw plot-render))
>
> ;; ---
>
> When I had a student implement the first plot version, I intentionally
> made sure that plot returned something I could use in big-bang.
>
> And btw, this works too:
>
> #lang racket
>
> (require (prefix-in p: plot) 2htdp/universe 2htdp/image)
>
> (define (plot-render world)
>   (overlay
>    (p:plot (p:lines (world->list-of-vectors world)
>                     #:color 6 #:label "Random walk"))
>    (square 800 'solid 'blue)))
>
> (define (world->list-of-vectors world)
>   `(#(1 3) #(2 -2) #(4 3)))
>
> (define (random-walk world)
>   'more-dummy)
>
> (big-bang 'dummy ; init
>           (on-tick random-walk 1)
>           (to-draw plot-render))
>
>
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