Q: having problem when define a table type in PL/SQL

Hi group, I am having a problem when try to define a table type in PL/SQL. The code fragment is as follows:         

        TYPE table_type IS TABLE OF number INDEXED BY BINARY_INTEGER;

	error message:
	Encountered the symbol "OF" when expecting one of the following "[" 
	Fatal syntax error unable to recover.

I am using FORM 4.5 on a window 3.1 system. Lots of thanks.