(defun chunk (n list &optional (acc '()))
    (if (> n (length list))
    acc
    (chunk n
           (subseq list 1)
           (cons (subseq list 0 n)
             acc))))

(defun hash-set (hash key value)
  (setf (gethash key hash) value))

(defun hash-count-incr (hash key count)
  (let ( (value (gethash key hash)) )
    (if (not value)
    (hash-set hash key count)
    (hash-set hash key (+ count value)))))

;; inifinite loop...?

(defun file->n-grams (n file-name)
  (let ((n-gram-table (make-hash-table :test #'equal)))
    (with-open-file (stream file-name)
      (loop :for line := (read-line stream nil nil)
        :while line :do
       (mapcar (lambda (c) (hash-count-incr n-gram-table c 1))
           (chunk n (str:split " " (string-downcase (string line)))))))
    n-gram-table))