%EOF returns '1' if the most recent read operation or write to
a subfile ended in an end of file or beginning of file condition;
otherwise, it returns '0'.
The following operations, if successful, set %EOF(filename)
off. If the operation is not successful, %EOF(filename) is not changed.
%EOF with no parameter is not changed by these operations.
When a full-procedural file is specified, this function returns
'1' if the previous operation in the list above, for the specified
file, resulted in an end of file or beginning of file condition. For
primary and secondary files, %EOF is available only if the file name
is specified. It is set to '1' if the most recent input operation
during *GETIN processing resulted in an end of file or beginning of
file condition. Otherwise, it returns '0'.
This function is allowed for input, update, and record-address
files; and for display files allowing WRITE to subfile records.