Two functions modify lists that are the values of variables.
-@defun add-to-list symbol element &optional append
+@defun add-to-list symbol element &optional append compare-fn
This function sets the variable @var{symbol} by consing @var{element}
onto the old value, if @var{element} is not already a member of that
value. It returns the resulting list, whether updated or not. The
value of @var{symbol} had better be a list already before the call.
-Membership is tested using @code{equal}.
+@code{add-to-list} uses @var{compare-fn} to compare @var{element}
+against existing list members; if @var{compare-fn} is @code{nil}, it
+uses @code{equal}.
Normally, if @var{element} is added, it is added to the front of
@var{symbol}, but if the optional argument @var{append} is
destructively. See @ref{Sets And Lists}.
@end defun
+@defun memql object list
+The function @code{memql} tests to see whether @var{object} is a member
+of @var{list}, comparing members with @var{object} using @code{eql},
+so floating point elements are compared by value.
+If @var{object} is a member, @code{memql} returns a list starting with
+its first occurrence in @var{list}. Otherwise, it returns @code{nil}.
+
+Compare this with @code{memq}:
+
+@example
+@group
+(memql 1.2 '(1.1 1.2 1.3)) ; @r{@code{1.2} and @code{1.2} are @code{eql}.}
+ @result{} (1.2 1.3)
+@end group
+@group
+(memq 1.2 '(1.1 1.2 1.3)) ; @r{@code{1.2} and @code{1.2} are not @code{eq}.}
+ @result{} nil
+@end group
+@end example
+@end defun
+
The following three functions are like @code{memq}, @code{delq} and
@code{remq}, but use @code{equal} rather than @code{eq} to compare
elements. @xref{Equality Predicates}.
@code{delete-dups} keeps the first one.
@end defun
- See also the function @code{add-to-list}, in @ref{Setting Variables},
+ See also the function @code{add-to-list}, in @ref{List Variables},
for another way to add an element to a list stored in a variable.
@node Association Lists