sformat and some tests

*scratch*.el

(defun sformat/replacer (text values match-data)
  (cond
    ((functionp values)
     ;; We don't need to save it, the caller does that
     (set-match-data match-data)
     ;; Call the user function to return the valuyes
     (funcall values text))
    ((hash-table-p values)
     (gethash text values))
    ((sequencep values)
     (elt values (string-to-number text)))))

(defun* sformat (template values)
  (let ((saved-match-data (match-data))
        (vtype
         (cond
           ((or (functionp values)
                (hash-table-p values)) :strings)
           ((or (listp values)
                (vectorp values)) :sequence))))
    (unwind-protect
         (replace-regexp-in-string
          (case vtype
            (:strings "\\${\\([^}]+\\)}")
            (:sequence "\\$\\([0-9]+\\)"))
          (lambda (text)
            (let ((in-matcher-data (match-data)))
              (unwind-protect
                   (sformat/replacer
                    (match-string 1 text)
                    values
                    saved-match-data)
                (set-match-data in-matcher-data)))) template)
      (set-match-data saved-match-data))))

(sformat
 "help ${name}! I'm ${malady}"
 #s(hash-table test equal data ("name" "nic" "malady" "on fire")))

(sformat
 "help ${name}! I'm ${malady}"
 (lambda (key)
   (case (intern key)
     ('name "nic")
     ('malady "on a plane!"))))