this piece of parenscript:

(defun my-element-by-id (cache id) (return (or (slot-value cache id) (setf (slot-value cache id) (document.get-element-by-id id)))))

gets transformed to:

function myElementById(cache, id) { return cache[id] || cache[id] = document.getElementById(id); };

which i believe is wrong -- browsers interpret it (according to JS operator priority rules, i guess) as

return (cache[id] || cache[id]) = document.getElementById(id);

and complain about wrong assignment to non-lvalue.

while with correctly set parentheses it works fine:

function myElementById(cache, id) { return cache[id] || (cache[id] = document.getElementById(id)); };

so, i guess, parenscript should detect this operator priority problem and insert parentheses correctly?