Added some empty commands

pga.ml

@@ -7,12 +7,16 @@ let main () =
     prerr_endline "command:";
     prerr_endline "  help        show this help page";
     prerr_endline "  echo TERM   pretty-print a program";
+    prerr_endline "  norm TERM   get the norm of a program";
+    prerr_endline "  i TERM      get the ith instruction of a program";
+    prerr_endline "  dot TERM    generate Dot code for a flow graph";
     prerr_endline "input program syntax:";
     prerr_endline "  - write star (*) instead of omega sign";
     prerr_endline "  - write dollar sign ($) instead of pound sign";
     prerr_endline "";
     prerr_endline "A TERM argument may also be omitted and passed on stdin";
-    prerr_endline "instead for convenient use of UNIX pipes";
+    prerr_endline "instead for convenient use of UNIX pipes, e.g.:";
+    prerr_endline "$ ./pga echo 'a;b;(c)*' | ./pga dot | dot -T png | display";
     exit status
   in
 
@@ -35,6 +39,8 @@ let main () =
         usage 0
       | "echo" ->
         print_endline (string_of_program (input_term 2))
+      | "norm" | "i" | "dot" ->
+        raise (Failure "not implemented")
       | _ ->
         usage 1
     with