Programming style

• Always put parenthesis after the previous expression on its line, never on a line by itself. If you have trouble reading code formatted in this way, ignore the parens (or make them disappear by regexp-replace or font lock) and look at indentation.
• Use long, descriptive variable names. It's +buffer-size+, not +BUFSIZ+ or similar. This immensely helps reading comprehension and generally alleviates the need to comment the code (see below). I can't bring myself to read uncommented code in languages that don't allow hyphens in variable names, while I can read people's Lisp just fine. It doesn't apply when abbreviations are widely known (e.g.retval, i). Also abbreviate extremely long symbol names, e.g. frobnicate-svuc might be preferred to frobnicate-slot-value-using-class if the code is expected to fit in 80 columns.
• Comment non-obvious stuff. For instance, once I wrote the following code:

  (defmacro fn (&environment env &body body)
    (with-walker-configuration (:undefined-reference-handler nil)
      ;; .VARS is modified implicitly in macroexpansion of the form
      ;; package protects against leaking symbols
      (let* ((.vars nil)
             (macro-name (gensym))
             (ret (macroexpand-all `(macrolet ((,macro-name ()
                                                 (car (push (gensym) .vars))))
                                      (symbol-macrolet ((_ (,macro-name)))
                                        (progn . ,body)))
                                   env)))
        (declare (special .vars))
        `(lambda ,(reverse .vars)
           ,ret))))

  and had to add the comment because it wasn't immediately obvious what this code does.
• Instead of (if some-list .. ...) use (if (not (endp some-list)) ... ...). Instead of (if (lookup foo) ... ...) use (if (not (null (lookup foo))) ... ...). Basically, only use a bare expression in conditionals if it uses the -p convention.

• Norvig's Tutorial on Good Lisp Programming Style (PDF).
• Riastradh's Lisp Style Rules(TXT).
• FAQ: How can I improve my Lisp programming style and coding efficiency?
• Novak's Lisp Style and Efficiency
• Chris Riesbeck's EECS 325 Lisp Style

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