From Letters

http://programmingpraxis.com/2010/11/30/form-letters/

import re
def from_letters(message, seq):
    def repl(m):
        i = int(m.group(2))
        return m.group(1)+seq[i]
    return re.sub(r'([^\$])\$(\d+)', repl, message)

S = """
Welcome back, $1!
We hope that you and all the members
of the $0 family are constantly
reminding your neighbors there
on $5 to shop with us.
As usual, we will ship your order to
    $3 $1 $2. $0
    $4 $5
    $6, $7 $8
"""

seq = ['Public', 'Jane', 'Q', 'Ms.', '600', 'Maple Street', 'Your Town', ' Iowa', '12345']
seq2 = ['Smith', 'John', 'Z', 'Dr.', '1234', 'Main Street', 'Anytown', 'Missouri', '63011']
print from_letters(S, seq)
print from_letters(S, seq2)

scheme

"\\12345"が上手く置換できないバグがある。

(use gauche.experimental.lamb)
(define S "
Welcome back, $1!
We hope that you and all the members
of the $0 family are constantly
reminding your neighbors there
on $5 to shop with us.
As usual, we will ship your order to
    $3 $1 $2. $0
    $4 $5
    $6, $7 $8
")

(define (from-letters s seq)
  (let* ((rx-generator (compose string->regexp (cut format #f "([^\\$])\\$~a" <>)))
         (rxs (list-tabulate (length seq) rx-generator))
         (args (apply append (zip rxs (map (cut format "\\1:~a" <>) seq))))) ;;\\12345となってしまう。
    (apply regexp-replace-all* s args)))

(let1 seq '("Public" "Jane" "Q" "Ms." "600" "Maple Street" "Your Town" " Iowa" "12345")
  (from-letters S seq))

追記

先読み、後読みの正規表現を使うとよい。

先読み否定	(?!)
先読み肯定	(?=)
後読み否定	(?)
後読み肯定	(?<=)

scheme

(use text.tree)

(define (from-letters s seq)
  (let1 vseq (list->vector seq)
    (define (%replace str)
      (cond ((rxmatch #/^\d+/ str) 
             => (^m (let1 i (string->number (m 0))
                      (list (vector-ref vseq i) (m 'after)))))
            (else str)))
    (tree->string
     (map %replace (string-split s #/(?<!\$)\$(?=\d+)/)))))