Function: rx--expand-template

rx--expand-template is a byte-compiled function defined in rx.el.gz.

Signature

(rx--expand-template OP VALUES ARGLIST TEMPLATE)

Documentation

Return TEMPLATE with variables in ARGLIST replaced with VALUES.

Source Code

;; Defined in /usr/src/emacs/lisp/emacs-lisp/rx.el.gz
;; FIXME: Consider adding extensions in Lisp macro style, where
;; arguments are passed unevaluated to code that returns the rx form
;; to use.  Example:
;;
;;   (rx-let ((radix-digit (radix)
;;             :lisp (list 'any (cons ?0 (+ ?0 (eval radix) -1)))))
;;     (rx (radix-digit (+ 5 3))))
;; =>
;;   "[0-7]"
;;
;; While this would permit more powerful extensions, it's unclear just
;; how often they would be used in practice.  Let's wait until there is
;; demand for it.

;; FIXME: An alternative binding syntax would be
;;
;;   (NAME RXs...)
;; and
;;   ((NAME ARGS...) RXs...)
;;
;; which would have two minor advantages: multiple RXs with implicit
;; `seq' in the definition, and the arglist is no longer an optional
;; element in the middle of the list.  On the other hand, it's less
;; like traditional lisp arglist constructs (defun, defmacro).
;; Since it's a Scheme-like syntax, &rest parameters could be done using
;; dotted lists:
;;  (rx-let (((name arg1 arg2 . rest) ...definition...)) ...)

(defun rx--expand-template (op values arglist template)
  "Return TEMPLATE with variables in ARGLIST replaced with VALUES."
  (let ((bindings nil)
        (value-tail values)
        (formals arglist))
    (while formals
      (pcase (car formals)
        ('&rest
         (unless (cdr formals)
           (error
            "Expanding rx def `%s': missing &rest parameter name" op))
         (push (cons (cadr formals) value-tail) bindings)
         (setq formals nil)
         (setq value-tail nil))
        (name
         (unless value-tail
           (error
            "Expanding rx def `%s': too few arguments (got %d, need %s%d)"
            op (length values)
            (if (memq '&rest arglist) "at least " "")
            (- (length arglist) (length (memq '&rest arglist)))))
         (push (cons name (list (car value-tail))) bindings)
         (setq value-tail (cdr value-tail))))
      (setq formals (cdr formals)))
    (when value-tail
      (error
       "Expanding rx def `%s': too many arguments (got %d, need %d)"
       op (length values) (length arglist)))
    (let ((subst (rx--substitute bindings template)))
      (if (and subst (not (cdr subst)))
          (car subst)
        (error "Expanding rx def `%s': must result in a single value" op)))))