Typically, CLUE programmers need not be aware of contact realization. CLUE
realizes a contact automatically by calling the <#347#><TT>realize</TT><#347#>
function<A ID="348"><tex2html_anchor_invisible_mark></A> during the next call to <#349#><TT>process-next-event</TT><#349#><A ID="350"><tex2html_anchor_invisible_mark></A> after initialization.
However, there are cases when it is useful to invoke the <#351#><TT>update-state</TT><#351#><A ID="352"><tex2html_anchor_invisible_mark></A> function to cause realization
explicitly (see Section~<A HREF=<tex2html_cr_mark>#ch:contact-state#353><tex2html_cr_mark></A>). Contact programmers can use
the <#354#><TT>realized-p</TT><#354#> method<A ID="355"><tex2html_anchor_invisible_mark></A> to ensure that operations
which depend on the existence of contact server resources are not performed
before the contact has been realized. For example, graphics output to a contact
cannot occur before it is realized, because its window does not yet exist.