For example if i enter sequence of characters 

"Hello world" H = 1 e = 1 l = 3 o - 2 r = 1 w = 1 d = 1 

can some one help me 

I found this [code](http://rosettacode.org/wiki/Letter_frequency#Common_Lisp) online but i dont understand it i want a simpler one 

```
(defun letter-freq (file)
 (with-open-file (stream file)
  (let ((str (make-string (file-length stream)))
        (arr (make-array 256 :element-type 'integer :initial-element 0)))
    (read-sequence str stream)
    (loop for c across str do (incf (aref arr (char-code c))))
    (loop for c from 32 to 126 for i from 1 do
      (format t "~c: ~d~a"
        (code-char c) (aref arr c)
        (if (zerop (rem i 8)) #\newline #\tab))))))

(letter-freq "test.lisp")

```