show: Handle multiple values correctly.

While we're at it, make sure the output is pretty-printed in an
attractive way, and print semicolons down the left hand side to protect
any weird characters which appear from messing up the REPL state.

diff --git a/mdw-base.lisp b/mdw-base.lisp
index 59ea692..37a3068 100644 (file)
--- a/mdw-base.lisp
+++ b/mdw-base.lisp
@@ -53,11 +53,17 @@
      (defun ,name ,args ,@body)))
 
 (defmacro show (x)
-  "Debugging tool: print the expression X and its value."
+  "Debugging tool: print the expression X and its values."
   (let ((tmp (gensym)))
-    `(let ((,tmp ,x))
-       (format t "~&~S: ~S~%" ',x ,tmp)
-       ,tmp)))
+    `(let ((,tmp (multiple-value-list ,x)))
+       (format t "~&")
+       (pprint-logical-block (*standard-output* nil :per-line-prefix ";; ")
+        (format t
+                "~S = ~@_~:I~:[#<no values>~;~:*~{~S~^ ~_~}~]"
+                ',x
+                ,tmp))
+       (terpri)
+       (values-list ,tmp))))
 
 (defun stringify (str)
   "Return a string representation of STR.  Strings are returned unchanged;