A 0-sized bitmap in 2htdp is the neutral element for many operations. ;; [Listof Image] -> Image (define (composite l-of-images) (foldl beside empty-images l-of-images))
The inelegance of dealing with 1-element lists instead of all lists is beyond the pale. > On Aug 2, 2016, at 11:32 AM, Tony Garnock-Jones <to...@ccs.neu.edu> wrote: > > On 07/29/2016 12:26 PM, George Neuner wrote: >> I don't see any obvious utility in being allowed to create a zero >> sized bitmap. Likewise a widget or a canvas. > > It is useful when writing code that handles images generically. For > example, and this is a real example where the zero-size-bitmap error bit > me the other day, when rendering `2htdp/image`s to `bitmap%`s. > > Here's the code I have now: > > (define w (max 1 (image:image-width i))) > (define h (max 1 (image:image-height i))) > > where previously it was > > (define w (image:image-width i)) > (define h (image:image-height i)) > > I consider the `(max 1 ...)` to have made my code less elegant and more > brittle. > > *Negative* dimensions don't make sense. But zero dimensions do. (I feel > like I want to waffle about closure properties...) > >> IMO a zero dimension should be an error. If you don't know how big >> the bitmap should be, don't create it until you do. > > In the case I was facing, rendering `2htdp/image`'s `empty-image` to a > `bitmap%`, I knew exactly how big it should be: 0x0. I think supporting > 0x0 bitmaps makes good sense and helps avoid brittleness and inelegance. > > Tony > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
