ref: 352ab3f5f8eceb576afdfccbde7ab7cf93f69433
dir: /examples/bq.scm/
(define (bq-process2 x d)
(define (splice-form? x)
(or (and (pair? x) (or (eq? (car x) 'unquote-splicing)
(eq? (car x) 'unquote-nsplicing)
(and (eq? (car x) 'unquote)
(length> x 2))))
(eq? x 'unquote)))
;; bracket without splicing
(define (bq-bracket1 x)
(if (and (pair? x) (eq? (car x) 'unquote))
(if (= d 0)
(cadr x)
(list cons ''unquote
(bq-process2 (cdr x) (- d 1))))
(bq-process2 x d)))
(define (bq-bracket x)
(cond ((atom? x) (list list (bq-process2 x d)))
((eq? (car x) 'unquote)
(if (= d 0)
(cons list (cdr x))
(list list (list cons ''unquote
(bq-process2 (cdr x) (- d 1))))))
((eq? (car x) 'unquote-splicing)
(if (= d 0)
(list 'copy-list (cadr x))
(list list (list list ''unquote-splicing
(bq-process2 (cadr x) (- d 1))))))
((eq? (car x) 'unquote-nsplicing)
(if (= d 0)
(cadr x)
(list list (list list ''unquote-nsplicing
(bq-process2 (cadr x) (- d 1))))))
(else (list list (bq-process2 x d)))))
(cond ((symbol? x) (list 'quote x))
((vector? x)
(let ((body (bq-process2 (vector->list x) d)))
(if (eq? (car body) list)
(cons vector (cdr body))
(list apply vector body))))
((atom? x) x)
((eq? (car x) 'quasiquote)
(list list ''quasiquote (bq-process2 (cadr x) (+ d 1))))
((eq? (car x) 'unquote)
(if (and (= d 0) (length= x 2))
(cadr x)
(list cons ''unquote (bq-process2 (cdr x) (- d 1)))))
((or (> d 0) (not (any splice-form? x)))
(let ((lc (lastcdr x))
(forms (map bq-bracket1 x)))
(if (null? lc)
(cons list forms)
(if (null? (cdr forms))
(list cons (car forms) (bq-process2 lc d))
(nconc (cons list* forms) (list (bq-process2 lc d)))))))
(else
(let loop ((p x) (q ()))
(cond ((null? p) ;; proper list
(cons 'nconc (reverse! q)))
((pair? p)
(cond ((eq? (car p) 'unquote)
;; (... . ,x)
(cons 'nconc
(nreconc q
(if (= d 0)
(cdr p)
(list (list list ''unquote)
(bq-process2 (cdr p)
(- d 1)))))))
(else
(loop (cdr p) (cons (bq-bracket (car p)) q)))))
(else
;; (... . x)
(cons 'nconc (reverse! (cons (bq-process2 p d) q)))))))))
#|
tests
> ``(,a ,,a ,b ,@b ,,@b)
`(,a ,1 ,b ,@b (unquote 2 3))
> `(,a ,1 ,b ,@b (unquote 2 3))
(1 1 (2 3) 2 3 2 3)
(define a 1)
(bq-process2 '`(,a (unquote unquote a)) 0)
(define b '(unquote a))
(define unquote 88)
(bq-process2 '``(,a ,,,@b) 0)
; etc. => (1 88 1)
(define b '(a a))
(bq-process2 '``(,a ,,,@b) 0)
; etc. => (1 1 1)
|#
;; minimal version with no optimizations, vectors, or dotted lists
(define (bq-process0 x d)
(define (bq-bracket x)
(cond ((and (pair? x) (eq? (car x) 'unquote))
(if (= d 0)
(cons list (cdr x))
(list list (list cons ''unquote
(bq-process0 (cdr x) (- d 1))))))
((and (pair? x) (eq? (car x) 'unquote-splicing))
(if (= d 0)
(list 'copy-list (cadr x))
(list list (list list ''unquote-splicing
(bq-process0 (cadr x) (- d 1))))))
(else (list list (bq-process0 x d)))))
(cond ((symbol? x) (list 'quote x))
((atom? x) x)
((eq? (car x) 'quasiquote)
(list list ''quasiquote (bq-process0 (cadr x) (+ d 1))))
((eq? (car x) 'unquote)
(if (and (= d 0) (length= x 2))
(cadr x)
(list cons ''unquote (bq-process0 (cdr x) (- d 1)))))
(else
(cons 'nconc (map bq-bracket x)))))
#t