The compiler from my blog article

c.scm

(define emit printf)

(define (compile exp)
  (cond
    [(fixnum? exp)   (emit "push ~a~%" exp)]
    [(eq? '+ (car exp))    (begin
                              (compile (cadr exp))
                              (compile (caddr exp))
                              (emit "pop eax~%")
                              (emit "pop ebx~%")
                              (emit "add eax, ebx~%")
                              (emit "push eax~%"))]))

(define (compile-top exp)
  (emit "global start~%")
  (emit "start:~%")
  (compile exp)
  (emit "sub esp, 4~%") ; Mach-O special
  (emit "mov eax, 0x1~%")
  (emit "int 0x80~%"))

;(compile-top '(+ 1 2))
(compile-top '(+ (+ 21 21) (+ 64 64)))