Question

I am trying to create a procedure that has a user input a non-empty string and then returns a random letter from the input in a substring of length one.

i.e.

(pick-at-random "word")

~"w"

(pick-at-random "word")

~"r"

So far I’ve got:

    (define pick-at-random
      (lambda (s)
        (substring s (random(string-length s)) ())))

This gives me the position of the letter I want to display and I feel like where the () is, I should have some variable representing the start value of the substring and then add one to it. However, I don’t know how to do this. Simply put, I am asking how I can limit the substring to length one while using the random function in the start value.

Answer 1

You may use let to bind the random number to a variable.

(define pick-at-random
  (lambda (s)
    (let ((index (random (string-length s))))
      (substring s index (+ index 1)))))