Special Functions:

The purpose of the special functions is to set values into
memory locations, so that these values can be used by external
subroutines.  Invocation of any of these functions does not
cause control to leave BASIC, as it does with the USR and CALL
functions.  Thus, the functions may be used without having any
routine that actually uses their results.  One thing peculiar
about these functions is that they have no value.  That is,
no value is returned when they are used.  They may be used
nearly anywhere, except that they must be separated from all
other elements of an expression by commas, and if they are
used in an assignment statement (LET or FOR), they must be
the last elements of the expression.  Normally, they are used
in disk input/output statements, such as LOAD, SAVE, OPEN,
CLOSE, GET, PUT, etc. to pass useful parameters.  Another
thing common to all these functions is that once the function
is used, the associated parameter(s) remain that way until it
is used again.  That way, the functions only need to be used
when it a change is required from the current values.  The
parameters are all initialized to zero by the I/O section
when BASIC is first entered.


DISK(<numeric expression between 0 and 3>)
This function is normally used to specify the number of the
disk drive which you wish to select.  If the function is not
used, the last drive selected will be used.  The value
of <numeric expression> is placed in the location DISK.  See
appendix C for the address of the pointer.  The I/O section
normally initializes the DISK number to the currently logged drive.
Examples:  OPEN DISK(1),FILE(8),3,"DATATEST"
	   LOAD DISK(0),"STARTREK"

DO(<expression>,<expression>)
Each expression can be either a numeric expression or a
string expression.  If numeric, the 2-byte number is passed.
If string, the string's address is passed.  The first
expression is passed to location DO.  The second expression
is passed into location DOPARA.  The addresses of these
locations are in the address table at the beginning of BASIC.
See appendix C.  The main idea of the DO function is to use
the first expression to decide on the type of function, and
to use the second expression to pass the argument.  The present
I/O section does not support any particular DO operation.














				5-1