CHAPTER 8  Set Types  Figure 8.a  Synta\ diagram for  SetType  A set type provides a compact structure for recording a collection of  values having the same ordinal t) I)e. More precisely, a set type defines  the set of values that is the powe,\et of its base type, i.e., the set of all  possible subsets of values of the base type, including the empty set.  Therefore, a single value of a set t) pe is a set, and the elements of that set  are values of the base type. A set is also a random-access structure  whose elements all have the same base type, which must be an ordinal  type .  Operations valid for set vallil:s are assignment, the familiar set  operations (e.g., set union), equality. and selection of components by  testing for membership (see beloVo  I.  Set values may be built up from set  elements by the operation of se  1 construction. Implementations of  Pascal usually define limits for the  ~ize  of sets, which can be quite small  (e.g., the number bits in a machine·' word"). The limit applies directly to  the range of the base type of the set type.  76  .....  'l~==.:~_pa_Ck_ed_I-_-_-_--"-J~--./.  (~r------+l·IOrdinalType~ 