Question

The following procedure random-choice contains a procedure called choice:

(define (random-choice strategy-1 strategy-2) 
 (choice strategy-1
 strategy-2
 (lambda (ship-state) (= (random 2) 0))))

How do I create the procedure choice that chooses the two strategies at random?
Also can you explain how lambda can be passed as an argument from procedure to procedure?

Answer 1

Here’s an example of how you would choose a value at random, between two possible values:

(define (choice s1 s2)
  (if (zero? (random 2)) s1 s2))

The procedure returns the randomly chosen value, it’s up to you how to use it. And a lambda can be passed as an argument as any other value, there isn’t anything different about it. For example:

((choice (lambda (x) (first x))
         (lambda (x) (last  x)))
 '(1 2 3 4 5))

The above will select randomly between a strategy for picking either the first or the last element in a list, and then it applies the selection to a list. Run it several times, you’ll see that sometimes 1 is returned, and sometimes 5 is returned.