Hi, While trying to build a parse tree list using CREATE-SCANNER, in the attempts after first 2-3 tries, below code exhausts the whole system memory and halts the system. (defparameter *markup-transformations* (loop for (element syntax) on (list ;; Link formatting. :link-internal "\\[\\[" :link-external "\\[http://" :link-external "\\[https://" :link-external "\\[ftp://" ;; Text formatting. :text-italic-bold "'''''" :text-italic "'''" :text-bold "''" :text-underline "\\_\\_" :text-monospace "`" :text-superscript "\\^" :text-subscript ",," ;; Formattings requiring a fresh line. :header-3 "\\n=== " :header-2 "\\n== " :header-1 "\\n= " :code-start "\\n{{{" :code-end "\\n}}}" :blockquote "\\n ") by #'cddr collect (list element (cl-ppcre:create-scanner (string-append "^" syntax))))) After 15 minutes, still no OOM reactions. (SBCL 1.0.6) So I needed restart the machine. (And therefore, I cannot narrow down the problematic part of the code by bisectioning.) Do you have any ideas about the erronous line? Regards.