Overriding a buttons callback in Racket

I'm writing a calculator app, which will have the numbered buttons append their values to the text-field when they are clicked. I'm trying to create a new button class with a callback that is overriden so I don't have to add the same lambda function to every single instantiation of the button. In the canvas% the I can do this by overriding on-paint since on-paint calls the paint-callback, but I haven't found a similar solution in the button.

(define number-button% (class button%                       (super-new)                       (inherit get-label)                       (define/override (callback)                         (let ([value (send input-screen get-value)])                           (send input-screen set-value (string-append value (get-label)))))))  

And an example of what I'm trying to avoid

(define 7button (new button% [label "7"] [parent second-row]                       [callback (λ (b e)                                   (let ([value (send input-screen get-value)] [b-label (send b get-label)])                                     (send input-screen set-value (string-append value b-label))))]))  

Does anyone have any ideas? I'll write a macro if I have to.

https://stackoverflow.com/questions/65866210/overriding-a-buttons-callback-in-racket January 24, 2021 at 09:06AM