ob-lisp: more general handling of the default-directory value in lisp code

Once again, thanks to Mark Cox for raising these issues.

* lisp/ob-lisp.el (org-babel-lisp-dir-fmt): Defcustom for use in
  changing how/if the current directory is represented to lisp code.
  (org-babel-execute:lisp): More general handling of the default
  directory value.

lisp/ob-lisp.el

@@ -41,6 +41,12 @@
 (defvar org-babel-default-header-args:lisp '())
 (defvar org-babel-header-arg-names:lisp '(package))
 
+(defcustom org-babel-lisp-dir-fmt
+  "(let ((*default-pathname-defaults* #P%S)) %%s)"
+  "Format string used to wrap code bodies to set the current directory.
+For example a value of \"(progn ;; %s\\n   %%s)\" would ignore the
+current directory string.")
+
 (defun org-babel-expand-body:lisp (body params)
   "Expand BODY according to PARAMS, return the expanded body."
   (let* ((vars (mapcar #'cdr (org-babel-get-header params :var)))
@@ -73,13 +79,13 @@
     (with-temp-buffer
       (insert (org-babel-expand-body:lisp body params))
       (slime-eval `(swank:eval-and-grab-output
-		    ,(format "(let ((*default-pathname-defaults* %S)) %s)"
-			     (let ((dir (if (assoc :dir params)
+		    ,(let ((dir (if (assoc :dir params)
 					    (cdr (assoc :dir params))
 					  default-directory)))
-			       (when dir (concat "#P" dir)))
-			     (buffer-substring-no-properties
-			      (point-min) (point-max))))
+		       (format
+			(if dir (format org-babel-lisp-dir-fmt dir) "(progn %s)")
+			(buffer-substring-no-properties
+			 (point-min) (point-max)))))
 		  (cdr (assoc :package params)))))
    (org-babel-pick-name (cdr (assoc :colname-names params))
 			(cdr (assoc :colnames params)))