LISP structures are analogous to C structs or Pascal records. Here is an example:
> (defstruct foo
bar
baaz
quux)
FOO
This example defines a data type called foo which is a structure
containing 3 fields. It also defines 4 functions which operate on this
data type: make-foo, foo-bar, foo-baaz, and
foo-quux. The first one
makes a new object of type foo; the others access the fields of an
object of type foo. Here is how to use these functions:
> (make-foo)
#s(FOO :BAR NIL :BAAZ NIL :QUUX NIL)
> (make-foo :baaz 3)
#s(FOO :BAR NIL :BAAZ 3 :QUUX NIL)
> (foo-bar *)
NIL
> (foo-baaz **)
3
The make-foo function can take a keyword argument for each of the
fields a structure of type foo can have. The field access functions
each take one argument, a structure of type foo, and return the
appropriate field.
See below for how to set the fields of a structure.