is a predicate for applications which consist only of Tcl code (no C extensions or packages).

PRO:
   * portable, will run on most or all platforms
   * easily edited even in deployed form

CON:
   * may run slower, especially in number-crunching
   * may expose implementation details that the end user is not supposed to know

In general, it is sensible to start coding an app in pure Tcl, and replace only those parts (if any) with C code that are just too slow. (But CPUs are picking up speed considerably faster than C coders ;-) ([RS])