In Racket, is it possible to have multiple event-handlers in big-bang?

问题

I am wanting to do two different things at each tick. Is it possible to have multiple on-tick event handlers in a big-bang environment?

This is what I would like to do:

(big-bang world

  (on-draw show-world)

  (on-tick event1 event2 1))

or

(big-bang world

  (on-draw show-world)

  (on-tick event1 1)

  (on-tick event2 1))

Neither of these methods is allowed. Is there a way to do this?

Thank you.

回答1:

What would it mean?

For example, suppose that

;; A World is a Nat (a natural number).

and here are the two tick handlers:

;; advance-by-one : World -> World
(define (advance-by-one w)
  (add1 w))

;; reset-at-ten : World -> World
(define (reset-at-ten w)
  (if (< w 10) w 0))

If the current World is 9, then what would you expect the next World to be? (I can think of two plausible answers; you have to pick one.)

Can you define another function that has the meaning you want and just use that (single) function as the tick handler? (Hint: you should use the two existing handler functions rather than trying to merge their definitions into one big function.)

(If you've made it to ISL:) What if you had three handlers, or four, or ten, that you wanted to compose together? Can you design a function that takes a list of handlers and produces a single handler function?

来源：https://stackoverflow.com/questions/53663171/in-racket-is-it-possible-to-have-multiple-event-handlers-in-big-bang