Questions relating to editing code in Lisp-like languages (i.e., Common Lisp, Scheme and similar), and working with Lisp read-eval-print loops. Questions about specific languages should use the tag for that language (e.g., [common-lisp], [guile]). Note that Emacs's Lisp dialect is Emacs Lisp, with the tag [elisp].
Note: questions about editing Lisp in Emacs are on-topic, but general LIsp programming questions are not.
I would like to validate the argument to a function before its action is executed. The main concern is the passing of a void variable. How can I trap this?
(if (boundp 'item)...
https://sep.yimg.com/ty/cdn/paulgraham/onlisp.pdf On page 36 Paul writes the following:
The conditions above do not guarantee the perfect locality you get
with purely functional code, though they do ...
I am starting to learn elisp and working through this tutorial https://www.gnu.org/software/emacs/manual/html_node/eintr/kill_002dnew-function.html
and I do not understand this basic example: