Like an ordinary Scheme procedure, a generic procedure takes arguments, performs a series of operations, and perhaps returns useful values. An ordinary procedure has a single body of code that is always executed when the procedure is called. A generic procedure has a set of multiple bodies of code, called methods, from which a subset is selected for execution. The selected bodies of code and the manner of their combination are determined by the classes of one or more of the arguments to the generic procedure.
Ordinary procedures and generic procedures are called with identical procedure-call syntax.
Generic procedures are true procedures that can be passed as arguments,
returned as values, and otherwise used in all the ways an ordinary
procedure may be used. In particular, generic procedures satisfy the
predicate procedure?.