(DEFINE-FUNCTION Hamlet (intext-or-file &KEY (order 3) (samples 5) (using NIL))
 "(HAMLET text-or-file [ORDER n] [SAMPLES n] [USING model])
   - Makes a markov model given training text
   - text-or-file may be a file name or a string of text
   - The order of the model is 3 unless ORDER is specified
   - Text generated by the model is displayed, the number of units determined by
       the value of SAMPLE
   -  
  (LET* ((intext (ENSURE-LIST
           (COND
              ((LISTP intext-or-file) intext-or-file)
              ((NOT (STRINGP intext-or-file))
                 (ERROR "Hamlet requires either text or a file-name"))
              ((< (LENGTH intext-or-file) 32)
                  (FILE-TO-STRING intext-or-file))
              (T intext-or-file))))
         (boundary-char (CODE-CHAR 255))
         (boundary (MAKE-STRING order :INITIAL-ELEMENT boundary-char))
         (model-counts NIL)
         (model using))
 
 ;; COUNT TEXT (if model not provided)
    (WHEN (NOT model) 
       (FOR-EACH text IN intext
            AS bounded-text = (CONCATENATE 'STRING boundary text)
            DO (FOR-EACH start FROM 1 TO (- (LENGTH bounded-text) order 1)
                    AS end = (+ start order -1)
                    AS key = (GET-ELEMENT start TO end FROM bounded-text)
                    AS target = (GET-STRING-ELEMENT (+ end 1) FROM bounded-text)
                    DO (INCREMENT model-counts(key target))))
        
       ;; MAKE MODEL
       (FOR-EACH key IN (LABELS-OF model-counts DIMENSION 1)
            AS sum = (FOR-EACH target 
                            IN (LABELS-OF-SLICE model-counts(key))
                          SUM (VALUE-OF model-counts(key target)))
            DO (FOR-EACH target IN (LABELS-OF-SLICE model-counts(key))
                    DO (ASSIGN model(key target) 
                           = (/ (VALUE-OF model-counts(key target)) sum)))))
  
 ;; MAKE OUTPUT TEXT
    (LOOP 
         WITH iteration = 1
         WITH word = boundary
         WHILE (NOT (> iteration samples))
         AS p = (RANDOM 1.0)
         AS letter
           = (FOR-EACH target IN (LABELS-OF-SLICE model (word))
                  AS target-p = (VALUE-OF model(word target))
                  WHEN (> target-p p)
                    RETURN target
                  DO (ASSIGN p = (- p target-p))
                  FINALLY
                    (RETURN target))
         COLLECT letter INTO output-letters
         DO (ASSIGN word 
                = (JOIN (LIST (GET-ELEMENTS 2 TO 'end FROM word) letter)))
            (IF-TRUE (EQUAL letter ".")
                THEN (INCREMENT iteration))
         FINALLY (DISPLAY (JOIN output-letters)))
    (IF (NOT using) model)))