In Clojure.

[sourcecode lang="css"]

;; helpers

(defn build-string-step [search-criteria]
  (fn [built-so-far next-character]
    (if (search-criteria built-so-far next-character)
      built-so-far
      (conj built-so-far next-character))))

(defn make-string-transformer [f]
  (fn [string]
    (apply str
           (reduce (build-string-step f) [] string))))

;; solve exercise 1

(def rem-dups
     (make-string-transformer
      (fn [built-so-far next-character]
        (some #(= % next-character) built-so-far))))

;; solve exercise 2

(def squash-spaces
     (make-string-transformer
      (fn [built-so-far next-character]
        (and (= next-character \space) (= (last built-so-far) \space)))))

[/sourcecode]