The name foo is used by computer scientists as a
place holder, to represent the name of any desired object or
function. It is not the name of an actual object or function;
it serves only as an example, to explain a concept.
However, many users misinterpret this convention, and actually
type the command foo or foo(). Then they email the
package author to inform them that foo is not defined.
To avoid this correspondence, we have now defined an object
called foo.
The function foo() prints a message explaining that foo
is not really the name of a variable.
The function can be executed simply by typing foo
without parentheses.