Range Over Built in Racket

Our first program will demonstrate iterating over elements in a variety of built-in data structures using for. Let’s see how to use iteration with some of the data structures we’ve already learned.

#lang racket

(define (sum-list lst)
  (define sum 0)
  (for ([num lst])
    (set! sum (+ sum num)))
  (displayln (format "sum: ~a" sum)))

(define nums '(2 3 4))
(sum-list nums)

(for ([i nums]
      [num (in-indexed nums)])
  (when (= (cdr num) 3)
    (displayln (format "index: ~a" (car num)))))

(define kvs (hash "a" "apple" "b" "banana"))
(for ([(k v) (in-hash kvs)])
  (displayln (format "~a -> ~a" k v)))

(for ([k (in-hash-keys kvs)])
  (displayln (format "key: ~a" k)))

(for ([p (in-string "go")])
  (displayln (format "~a ~a" (char-index p) (char->integer (char-value p)))))

To run the program, save the code in a file named range-over-built-in-types.rkt and then use the Racket interpreter to execute it.

$ racket range-over-built-in-types.rkt
sum: 9
index: 1
a -> apple
b -> banana
key: a
key: b
0 103
1 111

We’ve seen how to iterate over lists, hash tables, and strings in Racket. Now, let’s explore more about the language.

Recursion in Racket

Pointers in Racket

Learn X By Example

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Range Over Built in Racket