Description:

• The variable void represents the functional result of a side-effect or an empty argument. It is used only in combination with the applications of procedures or identifiers bound through externalproc to external procedures.
  
  The void result produced by a procedure or an external procedure is not printed at the prompt. However, it is possible to print it out in a print statement or in complex data types such as lists.
  
  The void argument is implicit when giving no argument to a procedure or an external procedure when applied. It can nevertheless be given explicitly. For example, suppose that foo is a procedure or an external procedure with a void argument. Then foo() and foo(void) are correct calls to foo. Here, a distinction must be made for procedures having an arbitrary number of arguments. In this case, an implicit void as the only parameter to a call of such a procedure gets converted into an empty list of arguments, an explicit void gets passed as-is in the formal list of parameters the procedure receives.
• void is used also as a type identifier for externalproc. Typically, an external procedure taking void as an argument or returning void is bound with a signature void -> some type or some type -> void. See externalproc for more details.