#s(name slot1 value1 slot2 value2 ...)
denotes a structure. This is valid only if name is the name
of a structure type already defined by defstruct
and if the structure type has a standard constructor function.
Let cm stand for the name of this constructor function;
then this syntax is equivalent to
#.(cm keyword1 'value1 keyword2 'value2 ...)
where each keywordj is the result of computing
(intern (string slotj) (find-package 'keyword))
The net effect is that the constructor function is called with the specified slots having the specified values.
(This coercion feature is deprecated; in the future, keyword names will
be taken in the package they are read in, so symbols that are
actually in the KEYWORD package should be used if that is what is desired.)
Whatever object the constructor function returns
is returned by the #S syntax.
For information on how the Lisp printer prints structures, see Printing Structures.