Source: http://en.wikibooks.org/wiki/Clojure_Programming#Norvig.27s_...

  (defn words [text] (re-seq #"[a-z]+" (. text (toLowerCase))))

  (defn train [features]
    (reduce (fn [model f] (assoc model f (inc (get model f 1)))) 
            {} features))

  (def *nwords* (train (words (slurp "big.txt"))))

  (defn edits1 [word]
    (let [alphabet "abcdefghijklmnopqrstuvwxyz", n (count word)]
      (distinct (concat
        (for [i (range n)] (str (subs word 0 i) (subs word (inc i))))
        (for [i (range (dec n))]
          (str (subs word 0 i) (nth word (inc i)) (nth word i) (subs word (+ 2 i))))
        (for [i (range n) c alphabet] (str (subs word 0 i) c (subs word (inc i))))
        (for [i (range (inc n)) c alphabet] (str (subs word 0 i) c (subs word i)))))))

  (defn known [words nwords] (for [w words :when (nwords w)]  w))

  (defn known-edits2 [word nwords] 
    (for [e1 (edits1 word) e2 (edits1 e1) :when (nwords e2)]  e2))

  (defn correct [word nwords]
    (let [candidates (or (known [word] nwords) (known (edits1 word) nwords) 
                         (known-edits2 word nwords) [word])]
      (apply max-key #(get nwords % 1) candidates)))

Python:

  def words(text): return re.findall('[a-z]+', text.lower())

  (def words (text) (tokens (downcase text) [~<= #\a _ #\z]))

      (bayes-train (map lower-case (parse (read-file {big.dms}) {\W} 0)) 'Lexicon)
      (define (edits1 word) 
       (let ((l (length word)) (res '()))
        (for (i 0 (- l 1)) (push (replace (nth i (string word)) (string word) "") res -1))
        (for (i 0 (- l 2)) (push (swap i (+ i 1) (string word)) res -1))
        (for (i 0 (- l 1)) (for (c (char "a") (char "z")) 
          (push (replace (nth i (string word)) (string word) (char c)) res -1)
          (push (replace (nth i (string word)) (string word) (string (char c) (nth i (string word)) )) res -1)))
        res))
      (define (edits2 word) (unique (flat (map edits1 (edits1 word)))))
      (define (known-edits2 word) (filter (fn (w) (Lexicon w)) (edits2 word)))
      (define (known words) (filter (fn (w) (Lexicon w)) words))
      (define (correct word)
        (let ((candidates (or (known (list word)) (known (edits1 word)) (known (edits2 word)))))
          (first (sort candidates (fn (w1 w2) (> (Lexicon w1) (Lexicon w2)))))))

      (join (map correct (parse "tihs sentnce is ful of inkorrect spelingz")) " ")
      
      this sentence is full of incorrect spelling