1 CALL
 The CALL statement transfers  control  to  a  BASIC  subprogram  or  other
 callable  routine.  You can pass optional arguments to the routine and can
 specify how these arguments are to be passed.   When  the  called  routine
 finishes executing, control returns to the calling program.

 Example

 CALL SUB1 BY REF (A$, Z BY VALUE, D$() BY DESC)

2 Syntax

     CALL routine [ pass-mech ] [ ( [ actual-param ],... ) ]

       routine:  { sub-name              }
                 { any callable routine  }

       pass-mech:  { BY REF   }
                   { BY VALUE }
                   { BY DESC  }

       actual-param:  { exp                              }
                      { array ( [,]... ) } [ pass-mech ] }

2 Passing_mechanisms
 The term "parameter passing mechanism" refers to the way in  which  data
 is  passed  to  a  subprogram.   BASIC  supports three parameter passing
 mechanisms with the following BY clauses:  BY  VALUE,  BY  REF,  and  BY
 DESC.   By  default,  BASIC  passes  and receives scalar numeric data by
 reference, and strings and arrays by descriptor.  All BASIC FUNCTION and
 SUB subprograms receive parameters BY REF or BY DESC.

 If a program consists entirely of BASIC program modules, you should  not
 specify  any  parameter  passing  mechanism.  However, other programming
 languages may not pass or receive parameters in the same way.   You  may
 have  to  specify  a  parameter passing mechanism when calling non-BASIC
 programs.