win_registry_get_value(+Key, 
+Name, -Value)Windows only. Fetches the value of a Windows registry key. Key 
is an atom formed as a path name describing the desired registry key.
Name is the desired attribute name of the key. Value 
is unified with the value. If the value is of type DWORD, 
the value is returned as an integer. If the value is a string, it is 
returned as a Prolog atom. Other types are currently not supported. The 
default‘root’is HKEY_CURRENT_USER. Other roots 
can be specified explicitly as
HKEY_CLASSES_ROOT, HKEY_CURRENT_USER,
HKEY_LOCAL_MACHINE or HKEY_USERS. The example 
below fetches the extension to use for Prolog files (see README.TXT 
on the Windows version):
?- win_registry_get_value(
       'HKEY_LOCAL_MACHINE/Software/SWI/Prolog',
       fileExtension,
       Ext).
Ext = pl