Mark H Weaver <[email protected]> skribis:
> + ((_ check? struct-expr ((getter . rest) expr) ...)
> + ;;
> + ;; FIXME: Improve compile-time error reporting:
> + ;; 1. report an error if any getter-path is a
> + ;; prefix of any other getter-path.
> + ;; 2. report an error if the initial getters
> + ;; do not all belong to the same record type.
> + ;;
> + ;; forest : (tree ...)
> + ;; tree : (getter (rest . expr) ...)
> + (let ((forest
> + (fold (lambda (g r e forest)
> + (cond ((find (lambda (tree)
> + (free-identifier=? g (car tree)))
> + forest)
> + => (lambda (tree)
> + (cons (cons g (cons (cons r e)
> + (cdr tree)))
> + (delq tree forest))))
> + (else (cons (list g (cons r e))
> + forest))))
> + '()
> + #'(getter ...)
> + #'(rest ...)
> + #'(expr ...))))
BTW this will need some more comments ;-), and perhaps splitting in
several functions for clarity. Using SRFI-1 alists and ‘match’ may help
as well. WDYT?
(I often find myself avoiding occurrences of ‘car’, ‘cdr’ & co. in my
code these days.)
FWIW I was using this approach to represent the tree of accessors:
(define (field-tree fields)
;; Given FIELDS, a list of field-accessor-lists, return a tree
;; that groups together FIELDS by prefix. Example:
;; FIELDS: ((f1 f2 f3) (f1 f4))
;; RESULT: ((f1 (f2 (f3)) (f4)))
(define (insert obj tree)
(match obj
((head tail ...)
(let ((sub (or (assoc-ref tree head) '())))
(cons (cons head (insert tail sub))
(alist-delete head tree))))
(()
tree)))
(fold-right insert '() fields))
Thanks,
Ludo’.
