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Checking for a member in a set: `memberp'
This abstraction is applicable for lists in general and also for sets
specifically checking, whether a certain element is contained in the list
or set.
The difference between the abstraction `locate' and `memberp'
consists in the first argument being a condition for `memberp'
and not a predicate function.
`memberp' appears in this category because it is used by the abstraction
`create a union of two sets'.
![\begin{lstlisting}[language=Scm]{}
(define memberp (lambda(x s)
(if (nullp s)
false
(if (equaln x (car s)
true
(memberp x (cdr s)))))))
\end{lstlisting}](img138.gif)
![\begin{lstlisting}[language=Scm]{}
(define l1 (cons one (cons two (cons three
...
...rp three l1))
--> true
;
(bdisp! (memberp five l1))
--> false
\end{lstlisting}](img139.gif)
Georg P. Loczewski
2004-03-05