The member type specifier can be used to represent ``symbolic'' values, analogous to the enumerated types of Pascal. For example, the second value of find-symbol has this type:
Member types are very useful for expressing consistency constraints on data structures, for example:(member :internal :external :inherited nil)
Member types are also useful in type inference, as the number of members can sometimes be pared down to one, in which case the value is a known constant.(defstruct ice-cream (flavor :vanilla :type (member :vanilla :chocolate :strawberry)))