string-join can add separators at beginning and end now

strings.lisp

@@ -14,12 +14,14 @@ replacement."
                       (princ (subseq string pos) str))))
         (repl 0)))))
 
-(defun string-join (sequence &optional (separator " "))
+(defun string-join (sequence &optional (separator " ") start end)
   "Concatenate the string representation of the elements of
-`sequence', with `separator' between consecutive elements."
+`sequence', with `separator' between consecutive elements. If `start'
+or `end' is non-nil, put the separator also there."
   (with-output-to-string (stream)
-    (le1 (first t)
+    (le1 (first (not start))
       (map nil (lambda (x)
                  (if first (setf first nil) (princ separator stream))
                  (princ x stream))
-           sequence))))
+           sequence))
+    (when end (princ separator stream))))