GNU Info

(emacs-lisp-intro.info)Build a list

---

Next: length Prev: cons Up: cons

---

Enter node , (file) or (file)node

Build a list
------------

   `cons' must have a list to attach to.(1)  You cannot start from
absolutely nothing.  If you are building a list, you need to provide at
least an empty list at the beginning.  Here is a series of `cons'
expressions that build up a list of flowers.  If you are reading this
in Info in GNU Emacs, you can evaluate each of the expressions in the
usual way; the value is printed in this text after `=>', which you may
read as `evaluates to'.

     (cons 'buttercup ())
          => (buttercup)
     
     (cons 'daisy '(buttercup))
          => (daisy buttercup)
     
     (cons 'violet '(daisy buttercup))
          => (violet daisy buttercup)
     
     (cons 'rose '(violet daisy buttercup))
          => (rose violet daisy buttercup)

In the first example, the empty list is shown as `()' and a list made
up of `buttercup' followed by the empty list is constructed.  As you
can see, the empty list is not shown in the list that was constructed.
All that you see is `(buttercup)'.  The empty list is not counted as an
element of a list because there is nothing in an empty list.  Generally
speaking, an empty list is invisible.

   The second example, `(cons 'daisy '(buttercup))' constructs a new,
two element list by putting `daisy' in front of `buttercup'; and the
third example constructs a three element list by putting `violet' in
front of `daisy' and `buttercup'.

   ---------- Footnotes ----------

   (1) Actually, you can `cons' an element to an atom to produce a
dotted pair.  Dotted pairs are not discussed here; see Note: Dotted
Pair Notation.