Problem Statement

Read a file one character at a time, as opposed to reading the entire file at once. The solution may be implemented as a procedure, which returns the next character in the file on each consecutive call (returning EOF when the end of the file is reached). The procedure should support the reading of files containing UTF8 encoded wide characters, returning whole characters for each consecutive read.

Let's start with the solution:

;; CLISP puts the external formats into a separate package
#+clisp (import 'charset:utf-8 'keyword)

(with-open-file (s "input.txt" :external-format :utf-8)
  (loop for c = (read-char s nil)
        while c
        do (format t "~a" c)))