>>(define y '(1 2 3 4)) >>(define dt 1) >>(define foo > (lambda (t) (do ((i 0 (+ i 1))) ((> i 3)) (if (and (>= t 0) (and (>= t > (* i dt)) (< t (* (+ i 1) dt)))) (list-ref y i) #f))))
DO does not return its body. It can be a little confusing. http://www.schemers.org/Documents/Standards/R5RS/HTML/r5rs-Z-H-7.html#%_sec_4.2.4 Also I think you have an extra AND there. You can have as many arguments to AND as you need, so doing (and 1 (and 2 3)) is the same as (and 1 2 3). You can accomplish the same thing with LET. I think this does what you want: > (define (foo t) > (let loop ((i 0)) > (if (and (>= t 0) (>= t (* i dt)) (< t (* (+ i 1) dt))) > (list-ref y i) > (if (> i 3) > #f > (loop (+ i 1))))))
