--- orig/lisp/cmuscheme.el
+++ mod/lisp/cmuscheme.el
@@ -127,6 +127,8 @@
 (define-key scheme-mode-map "\C-c\M-r" 'scheme-send-region-and-go)
 (define-key scheme-mode-map "\C-c\M-c" 'scheme-compile-definition)
 (define-key scheme-mode-map "\C-c\C-c" 'scheme-compile-definition-and-go)
+(define-key scheme-mode-map "\C-c\C-t" 'scheme-trace-procedure)
+(define-key scheme-mode-map "\C-c\C-x" 'scheme-expand-current-form)
 (define-key scheme-mode-map "\C-c\C-z" 'switch-to-scheme)
 (define-key scheme-mode-map "\C-c\C-l" 'scheme-load-file)
 (define-key scheme-mode-map "\C-c\C-k" 'scheme-compile-file) ;k for "kompile"
@@ -143,6 +145,10 @@
     '("Compile Definition & Go" . scheme-compile-definition-and-go))
   (define-key map [com-def]
     '("Compile Definition" . scheme-compile-definition))
+  (define-key map [exp-form]
+    '("Expand current form" . scheme-expand-current-form))
+  (define-key map [trace-proc]
+    '("Trace procedure" . scheme-trace-procedure))
   (define-key map [send-def-go]
     '("Evaluate Last Definition & Go" . scheme-send-definition-and-go))
   (define-key map [send-def]
@@ -153,7 +159,7 @@
     '("Evaluate Region" . scheme-send-region))
   (define-key map [send-sexp]
     '("Evaluate Last S-expression" . scheme-send-last-sexp))
-)
+  )
 
 (defvar scheme-buffer)
 
@@ -311,6 +317,69 @@
      (beginning-of-defun)
      (scheme-compile-region (point) end))))
 
+(defcustom scheme-trace-command "(trace %s)"
+  "*Template for issuing commands to trace a Scheme procedure.
+Some Scheme implementations might require more elaborate commands here.
+For PLT-Scheme, e.g., one should use
+
+   (setq scheme-trace-command \"(begin (require (lib \\\"trace.ss\\\")) (trace %s))\")
+
+For Scheme 48 and Scsh use \",trace %s\"."
+  :type 'string
+  :group 'cmuscheme)
+
+(defcustom scheme-untrace-command "(untrace %s)"
+  "*Template for switching off tracing of a Scheme procedure.
+Scheme 48 and Scsh users should set this variable to \",untrace %s\"."
+
+  :type 'string
+  :group 'cmuscheme)
+
+(defun scheme-trace-procedure (proc &optional untrace)
+  "Trace procedure PROC in the inferior Scheme process.
+With a prefix argument switch off tracing of procedure PROC."
+  (interactive
+   (list (let ((current (symbol-at-point))
+               (action (if current-prefix-arg "Untrace" "Trace")))
+           (if current
+               (read-string (format "%s procedure [%s]: " action current) nil nil (symbol-name current))
+             (read-string (format "%s procedure: " action))))
+         current-prefix-arg))
+  (when (= (length proc) 0)
+    (error "Invalid procedure name"))
+  (comint-send-string (scheme-proc)
+                      (format 
+                       (if untrace scheme-untrace-command scheme-trace-command)
+                       proc))
+  (comint-send-string (scheme-proc) "\n"))
+
+(defcustom scheme-macro-expand-command "(expand %s)"
+  "*Template for macro-expanding a Scheme form.
+For Scheme 48 and Scsh use \",expand %s\"."
+  :type 'string
+  :group 'cmuscheme)
+
+(defun scheme-expand-current-form ()
+  "Macro-expand the form at point in the inferior Scheme process."
+  (interactive)
+  (let ((current-form (scheme-form-at-point)))
+    (if current-form
+        (progn
+          (comint-send-string (scheme-proc)
+                              (format 
+                               scheme-macro-expand-command
+                               current-form))
+          (comint-send-string (scheme-proc) "\n"))      
+      (error "Not at a form"))))
+
+(defun scheme-form-at-point ()
+  (let ((next-sexp (thing-at-point 'sexp)))
+    (if (and next-sexp (string-equal (substring next-sexp 0 1) "("))
+        next-sexp
+      (save-excursion
+        (backward-up-list)
+        (scheme-form-at-point)))))
+
 (defun switch-to-scheme (eob-p)
   "Switch to the scheme process buffer.
 With argument, position cursor at end of buffer."