griffin(52)% rs
RScheme (v0.7.2, 97.12.21)
Copyright (C) 1995-1997 Donovan Kolbly <d.kolbly@rscheme.org>

top[0]=>(append '(1 2 3) '(4 5 6))
value := (1 2 3 4 5 6)


top[3]=>(define x '(1 2 3))
value := x
top[4]=>(define y '(4 5 6))
value := y
top[5]=>(append x y)    ;; append does not modify its parameters
value := (1 2 3 4 5 6)
top[6]=>x
value := (1 2 3)
top[7]=>y
value := (4 5 6)

top[9]=>(define (append l1 l2)
          (cond ((null? l1) l2)
                (else (cons (car l1) (append (cdr l1) l2)))
                ))

top[10]=>(append '(1 2 3) '(5 6 7))
value := (1 2 3 5 6 7)
top[11]=>
top[11]=>(reverse '(1 2 3 4))
value := (4 3 2 1)
top[12]=>(reverse '(1 2 (3 4) 5))
value := (5 (3 4) 2 1)

;;; this is the straightforward, but O(n^2), version of reverse
top[13]=>(define (rev l)
           (cond ((null? l) '())
                 (else (append (rev (cdr l))
                               (list (car l))))
                 ))
value := rev
top[14]=>(rev '(1 2 (3 4) 5))
value := (5 (3 4) 2 1)
top[15]=>
top[15]=>

;; here is the O(n) version

(define (newrev l accum)
           (cond ((null? l) accum)
                 (else (newrev (cdr l) (cons (car l) accum)))
                 ))


break[0]=>(newrev '(1 2 (3 4) 5) '())
value := (5 (3 4) 2 1)

break[1]=>(define (rev2 l)
            (newrev l '()))

break[2]=>(rev2 '(1 2 (3 4) 5))
value := (5 (3 4) 2 1)



top[0]=> ;; assignment using set!

top[0]=>(define x 7)
value := x
top[1]=>x
value := 7
top[2]=>(set! x (- x 1))
value := 6
top[3]=>x
value := 6
top[4]=>;; for modifying the car and cdr fields of a cons cell
top[4]=>;; use set-car! and set-cdr!

top[4]=>(define l '(1 2 3))
value := l
top[5]=>l
value := (1 2 3)
top[6]=>(set-car! l 4)
top[7]=>l
value := (4 2 3)
top[8]=>
top[8]=>(set-cdr! l '(5 6))
top[9]=>l
value := (4 5 6)
top[10]=>
top[10]=>(set-cdr! l l)
top[11]=>l
value := (4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 ...
top[12]=>(set! l '(4 5 6))
value := (4 5 6)
top[13]=>l
value := (4 5 6)
top[14]=>(set-car! l l)
top[15]=>l
value := (((((((((((((((((((((((((((((((((((((((((((((((((((((...
top[16]=>
top[16]=>
top[16]=>;; local variables are introduced using the LET construct
top[16]=>
top[16]=>(define (f x)
           (let ((y 3) (z 7))
             (+ x y z)))

top[17]=>(f 5)
value := 15
top[18]=>(+ 4 (let ((a 3)) a))
value := 7
top[19]=> (define (f x) (lambda (y) (+ x y)))
value := f
top[20]=>(define g (f 3))
value := g
top[21]=>(g 6)
value := 9
top[24]=>
top[24]=>(define h (let ((count 0))
                     (lambda () (set! count (+ count 1))
                                count)))
value := h
top[25]=>(h)
value := 1
top[26]=>(h)
value := 2
top[27]=>(h)
value := 3
top[28]=>count
runtime error: top-level-var `count' not bound

break[0]=>(define f h)
value := f
break[1]=>(f)
value := 4
break[2]=>(h)
value := 5