Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

■ The function defined by DEF FN cannot be called. More than
  one condition can cause this error:
 
  • The DEF FN function is undefined.
 
  • The DEF FN function calls another function that is
    undefined.
 
  • The DEF FN function attempts to call itself recursively.
 
■ If you need additional help, move the cursor to a keyword
  and press F1 to open the Help window.