20. Using BASIC in the Common Language
  Environment
  The BASIC compiler lets you call external routines from a
  BASIC program. This chapter shows you how to call the
  following:

  .
        External routines written in other OpenVMS languages
  .
        OpenVMS Run-Time Library routines
  .
        OpenVMS system services

  The terms routine, procedure, and function are used
  throughout this chapter. A routine is a closed, ordered
  set of instructions that performs one or more specific tasks.
  Every routine has an entry point (the routine name), and
  may or may not have an argument list. Procedures and
  functions are specific types of routines: a procedure is a
  routine that does not return a value, while a function is a
  routine that returns a value by assigning that value to the
  function's identifier.

  System routines are prewritten OpenVMS routines that
  perform common tasks such as finding the square root of
  a number or allocating virtual memory. You can call any
  system routine from BASIC provided that the data struc-
  tures necessary for that routine are supported. The system
  routines used most often are OpenVMS Run-Time Library
  routines and system services. System routines, which are
  discussed later in this chapter, are documented in detail in
  the OpenVMS Run-Time Library Routines Volume and the
  OpenVMS System Services Reference Manual .