ada and gnat (mingw)

[Hans Vlems <hvlems@freenet.de>]

This is not a real ADA language question and thus possibly off topic
but don't be too hard on a newbie :)
I want to use my own packages. Example:

package my_constants is

 cc_hyphen : constant character := '-';
 cc_comma : constant character := ',';
 cc_digit9   : constant character := '9';

end my_constants;

This file is stored as my_constants.adb (on a WIndows platform).
gnatmake my_constants.adb results in:
gnatmake: my_constants.adb:1:08: keyword "body" expected here [see
file name]

Inserting the reserverd word body after package on line 1 doesn't
help...
What am I doing wrong and where can I find information on how to drive
this compiler?
Hans

PS
Apologies for the OT post