In Lisp, all parameters are passed to a subprogram by passing pointers to the values.

In other languages, there are two primary ways of passing parameters.

Call by value is the default for all values in Pascal and for small parameters (e.g. integers and floats) in C++. With this method, a copy of the value of the parameter is made and sent to the procedure that is called.

• A change to a parameter is not seen by the calling program.

• This method is slower for large data, such as arrays.

Call by reference passes the address of the value to the procedure.

• A change to a parameter is seen by the calling program.

• This method is faster for large data, such as arrays.

In Pascal, the keyword var specifies call by reference.

   procedure sort( var arr: arraytype);

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