(define (ip2long ip)
(let
((quads (map (lambda (x) (string->number x)) (string-split ip #\.))))
(fold-left (lambda (x y) (+ (* x 256) y)) 0 quads)))

And the string-split function: (some Scheme compilers have it built-in)

; split string str by delimiter del
; returns list of strings
(define (string-split str del)
(let ((i (string-find-next-char str del)))
(if (false? i)
(cons str ())
(cons
(substring str 0 i)
(string-split
(substring str (+ i 1) (string-length str))
del)))))

I would be happy to hear comments on these too

Very interesting implementations for ip-to-int and int-to-ip.

The way you used map with two lists for ip-to-int was pretty clever – I didn’t even know you can pass many lists as arguments to map.

The unfold-right procedure was also new for me, I guess that’s because there is no built-in implementation for MIT-Scheme.

#lang mzscheme
(require srfi/1/list
srfi/14/char-set
srfi/13/string)

(define ip-to-int
(lambda (ip)
(apply +
(map *
(map string->number (string-tokenize ip (string->char-set “0123456789″)))
(map (lambda (x) (expt 256 x)) (iota 4 3 -1))))))

(define int-to-ip
(lambda (intip)
(string-join
(map
number->string
(unfold-right
zero?
(lambda (x) (remainder x 256))
(lambda (x) (quotient x 256))
intip))
“.”)))