Problem Statement

Load the entire contents of some text file as a single string variable. If applicable, discuss: encoding selection, the possibility of memory-mapping. Of course, in practice one should avoid reading an entire file at once if the file is large and the task can be accomplished incrementally instead (in which case check File IO); this is for those cases where having the entire file is actually what is wanted.

Let's start with the solution:

(defun file-string (path)
  (with-open-file (stream path)
    (let ((data (make-string (file-length stream))))
      (read-sequence data stream)
      data)))