do error checking

rpn.go

@@ -178,28 +178,18 @@ DESCRIPTION
         [no]debug            toggle debug output (nodebug turns it off)
         [no]showstack        show the last 5 items of the stack (noshowtack turns it off)
 
-    Show commands:
+    Show commands: dump display the stack contents hex show last stack item
+    in hex form (converted to int) history display calculation history vars
+    show list of variables
 
-        dump                 display the stack contents
+    Stack manipulation commands: clear clear the whole stack shift remove
-        hex                  show last stack item in hex form (converted to int)
+    the last element of the stack reverse reverse the stack elements swap
-        history              display calculation history
+    exchange the last two stack elements dup duplicate last stack item undo
-        vars                 show list of variables
+    undo last operation edit edit the stack interactively using vi or
+    $EDITOR
 
-    Stack manipulation commands:
+    Other commands: help|? show this message manual show manual
-
+    quit|exit|c-d|c-c exit program
-        clear                clear the whole stack
-        shift                remove the last element of the stack
-        reverse              reverse the stack elements
-        swap                 exchange the last two stack elements
-        dup                  duplicate last stack item
-        undo                 undo last operation
-        edit                 edit the stack interactively using vi or $EDITOR
-
-    Other commands:
-
-        help|?               show this message
-        manual               show manual
-        quit|exit|c-d|c-c    exit program
 
     Register variables:
 

rpn.pod

@@ -186,14 +186,12 @@ Configuration Commands:
     [no]showstack        show the last 5 items of the stack (noshowtack turns it off)
 
 Show commands:
-
     dump                 display the stack contents
     hex                  show last stack item in hex form (converted to int)
     history              display calculation history
     vars                 show list of variables
 
 Stack manipulation commands:
-
     clear                clear the whole stack
     shift                remove the last element of the stack
     reverse              reverse the stack elements
@@ -203,7 +201,6 @@ Stack manipulation commands:
     edit                 edit the stack interactively using vi or $EDITOR
 
 Other commands:
-
     help|?               show this message
     manual               show manual
     quit|exit|c-d|c-c    exit program