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CALL or CALLS (Non-BASIC Procedures) Details
 
Syntax
 
There are three different forms that can be used to perform this
function:
 
  CALL name [( call-argumentlist )]
  name [ call-argumentlist ]
  CALLS name [( calls-argumentlist )]
 
  Argument            Description
  name                The name of the procedure being called. A name
                      is limited to 40 characters.
  call-argumentlist   The variables or constants passed to the
                      procedure. The syntax of a call-argumentlist is
                      described below.
  calls-argumentlist  A list containing the variables and constants
                      that CALLS passes to the procedure. Entries are
                      separated by commas. Note that these arguments
                      are passed by reference as far addresses,
                      using the segment and offset of the variable.
                      You cannot use BYVAL and SEG in a calls-
                      argumentlist.
 
A call-argumentlist has the following syntax:
 
  [[{BYVAL|SEG}]argument][,[{BYVAL|SEG}]argument]...
 
If argument is an array, parentheses are required:
 
  [[{BYVAL|SEG}]argument[()]][,[{BYVAL|SEG}]argument]...
 
  Part       Description
  BYVAL      Indicates the argument is passed by value, rather than
             by near reference (the default)
  SEG        Passes the argument as a segmented (far) address
  argument   A BASIC variable, array, or constant passed to a
             procedure
 
CALLS is the same as using CALL with a SEG before each argument: every
argument in a CALLS statement is passed as a segmented address.
 
  Note: The syntax described above does not correctly invoke a BASIC
        procedure -- only procedures in other languages. See the
        ◄CALL (BASIC) statement► for the other syntax.
 
If the argument list of either statement includes an array argument,
the array is specified by the array name and a pair of parentheses:
 
  DIM IntArray(20) AS INTEGER
  .
  .
  .
  CALL ShellSort(IntArray() AS INTEGER)
 
When you use the CALL statement, the CALL keyword is optional.
However, when you omit CALL, you must declare the procedure
in a DECLARE statement. Notice also that when you omit CALL,
you also omit the parentheses around the argument list.
 
The result of the BYVAL keyword differs from BASIC's pass by value:
 
  CALL Difference (BYVAL A,(B))
 
For the first argument, only the value of A is passed to Difference.
In contrast, (B) is evaluated, a temporary location is created for
the value, and the address of the temporary location is passed to
Difference. You can use BASIC's pass by value for an argument, but
you must write the procedure in the other language so the procedure
accepts an address.
 
  Note: If name refers to an assembly-language procedure, it must be
        a PUBLIC name (symbol). PUBLIC names beginning with "$" and
        "_" may conflict with names used by the BASIC run-time system.
        Duplicate names cause a linker error message "Symbol already
        defined" to be generated.
 
Be careful using the SEG keyword to pass arrays because BASIC may move
variables in memory before the called routine begins execution.
Anything in an argument list that causes memory movement may create
problems. You can safely pass variables using SEG if the CALL
statement's argument list contains only simple variables, arithmetic
expressions, or arrays indexed without the use of intrinsic or user-
defined functions.
 
Differences from BASICA
 
Assembly-language programs invoked from BASICA that have string
arguments must be changed because the string descriptor is now four
bytes long. The four bytes are the low byte and high byte of the
length followed by the low byte and high byte of the address.
 
To locate the routine being called, the BASICA CALLS statement uses
the segment address defined by the most recently executed DEF SEG
statement. There is no need to use DEF SEG with the CALLS statement
because all arguments are passed as far (segmented) addresses.