nested let to nested lambdas

nested-let-wip.rkt

(define (last lst)
  (if (null? lst)
      null
      (if (null? (cdr lst))
          (car lst)
          (last (cdr lst)))))

; nested-lets->combination
; expected result:
; '((λ (a)
;     ((λ (b) ((λ (a) ((λ (c) ((λ (d) (display a) (newline) (display b) (newline) (display c) (newline) (display d) (newline)) (+ c 4))) (+ b 3))) (+ 1 1)))
;      (+ a 2)))
;   (+ 1 1))
(let ((let? (λ (exp) (eq? (car exp) 'let)))
      (let-assocs (λ (exp) (cadr exp)))
      (let-body (λ (exp) (cddr exp)))
      (make-lambda (λ (parameters body) (cons 'λ (cons parameters body))))
      (nested '(let ((a (+ 1 1)))
                 (let ((b (+ a 2)))
                   (let ((c (+ b 3)))
                     (let ((d (+ c 4)))
                       (display a)
                       (newline)
                       (display b)
                       (newline)
                       (display c)
                       (newline)
                       (display d)
                       (newline)))))))
  (let loop ((b (car (let-body nested))))
    (define assocs (let-assocs b))
    (define vars
      (if (null? assocs)
          null
          (map car assocs)))
    (define exps
      (cond
        ; empty associations
        ((null? assocs) null)
        ; only one association
        ((null? (cdr assocs)) (car assocs))
        ; malformed let
        ((not (pair? (cadr assocs)))
         (error "Malformed let associations -- NESTED-LETS->COMBINATION" assocs))
        (else (map cadr assocs))))
    (define exp (last exps))
    (cond ((let? (last b))
           (define top-var (caar (let-assocs nested)))
           (list (make-lambda (list top-var)
                              (cons (list (make-lambda vars (loop (last b)))) (list exp)))
                 (cadar (let-assocs nested))))
          (else
           (define ret (cons (make-lambda vars (let-body b)) (list exp)))
           (printf "ret: ~v~n" ret)
           ret))))