end type term record if tboolean then idname else subexexpression end end henceevery variable of type term consists of two componentsnamelythe tagfield andif is truethe field idor of the field subex otherwise consider nowfor examplethe following four expressions + ( ( ( ( /( ) these expressions may be visualized by the patterns in fig which exhibit their nestedrecursive structureand they determine the layout or mapping of these expressions onto store second example of recursive information structure is the family pedigreelet pedigree be defined by (the name ofa person and the two pedigrees of the parents this definition leads inevitably to an infinite structure real pedigrees are bounded because at some level of ancestry information is missing assume that this can be taken into account by again using conditional structuretype ped record if knownboolean then namenamefathermotherped end end note that every variable of type ped has at least one componentnamelythe tagfield called known if its value is truethen there are three more fieldsotherwise there is none particular value is shown here in the forms of nested expression and of diagram that may suggest possible storage pattern (see fig (tted(tfred(tadam( )( ))( ))(tmary( )(teva( )( )) fig storage patterns for recursive record structures