new: expand elisp macros

* elisp.el (elisp-macro-buffer): The buffer that displays the
expansion.

(elisp-macro-expand): Expand the macro, and either displays in a
temporary buffer, or replace the original region.  Right now this only
expands one form at a time.  I might want to modify this in the future
so that this will expand every form found in the region.  For now this
is enough for me.

(emacs-lisp-mode-map): Bind it to C-c C-e.

1 files changed, 32 insertions, 0 deletions

diff --git a/elisp.el b/elisp.el
index c944040..bb68713 100644
--- a/elisp.el
+++ b/elisp.el
@@ -310,6 +310,38 @@ PARSE-START is the starting position of the parse."
               (t
                normal-indent))))))
 
+;;; macro expansion
+
+(defconst elisp-macro-buffer "*ELisp-Macroexpand*"
+  "The name of the buffer that displays the expansion of \
+macros.")
+
+;;;###autoload
+(defun elisp-macro-expand (start end subst)
+  "Expand ELisp macros in the region.
+Normally display output in temp buffer, but
+prefix arg means replace the region with it.
+
+Note that this only expands one Emacs Lisp form.  So multiple
+forms have to be expanded separately.
+
+Adapted from `c-macro-expand'."
+  (interactive "r\nP")
+  (let ((form (read (buffer-substring-no-properties start end)))
+        (buf (cond ((not subst)
+                    (get-buffer-create elisp-macro-buffer)))))
+    (cond
+     ((not subst)
+      (with-current-buffer buf
+        (erase-buffer)
+        (insert (format "%s" (macroexpand-all form))))
+      (display-buffer buf))
+     (t
+      (delete-region start end)
+      (insert (format "%S" (macroexpand-all form)))))))
+
+(define-key emacs-lisp-mode-map (vector 3 5) #'elisp-macro-expand)
+
 (provide 'elisp)
 
 ;;; elisp.el ends here