(define-syntax let1*
(syntax-rules ()
((_ (((var0 val0) proc0 ...)) body ...)
((lambda (var0) proc0 ... body ...) val0))
((_ (((var0 val0) proc0 ...) ((var1 val1) proc1 ...) ...) body ...)
((lambda (var0)
proc0 ...
(let1* (((var1 val1) proc1 ...) ...) body ...))
val0))))
(define (multiple-dwellings)
(let1* (((fletcher (amb 1 2 3 4 5))
(require (not (= fletcher 1)))
(require (not (= fletcher 5))))
((cooper (amb 1 2 3 4 5))
(require (not (= cooper 1)))
(require (not (= (abs (- fletcher cooper)) 1)))
(require (not-member cooper (list fletcher))))
((smith (amb 1 2 3 4 5))
(require (not (= (abs (- smith fletcher)) 1)))
(require (not-member smith (list fletcher smith))))
((miller (amb 1 2 3 4 5))
(require (> miller cooper))
(require (not-member miller (list smith cooper fletcher))))
((baker (amb 1 2 3 4 5))
(require (not (= baker 5)))
(require (not-member baker (list miller smith cooper fletcher)))))
`((baker ,baker)
(cooper ,cooper)
(fletcher ,fletcher)
(miller ,miller)
(smith ,smith))))I wrote the attached macro today to remove some ugly lateral movement while optimizing the ‘multiple-dwelling’ procedure from SICP. If I was going to be writing in this non-deterministic language frequently I think I would change the interface a good bit (just look at that nasty repetition of ‘non-member’!), but this helps a good bit.