First Clojure example.


    ;;; Declarations:
    (def n 5)
    (defn f[x] (+ x 2))
    (f n)
    ;; Same as above
    (def f (fn[x] (+ x 2)))

    ;;; Clojure collections: Lists, vectors, maps
    ;; A list
    (def numbers '(1 3 -6 7 9))
    (first numbers)
    (rest numbers)

    ;; A vector
    (def myvec [5 8 9 0])
    (first myvec)
    (rest myvec)
    (seq myvec)
    ;; creating a vector from a list:
    (vec numbers)


    ;; A hashmap (a map)
    (def mymap {:a 6 :b "apple" :c [2 3]})
    ;; :a is a keyword
    (:a mymap)
    (mymap :b)
    (first mymap) ;; note: the order isn't guaranteed
    (rest mymap)
    (seq mymap)
    (keys mymap)
    (vals mymap)

    ;; Adding an element to a collection using conj (returns the same type of collection):
    (conj numbers 6)
    (conj myvec 6)
    (assoc mymap :x 5)
    (conj mymap [:x 5])
    (assoc mymap :a 1000)
    (conj mymap [:a 1000])

    ;; Adding a collection of elements using into:
    (into numbers ["a" "b" "c"])
    (into myvec ["a" "b" "c"])
    ;; into on a map takes a sequence of key/value pairs
    (into mymap [["a" "b"] ["c" "d"]])


    ;; nil
    (first '())
    ;; the rest of an empty sequence is an empty sequence, not nil:
    (rest '())
    ;;nil is not the same as empty sequence:
    (= '() nil)
    (nil? '())
    ;; lookup on a map that doesn't have the key returns nil:
    (:x mymap)

    ;; Functions that work on sequences.
    ;; A collection is first converted to its sequence, and then
    ;; the function is applied.
    (nth numbers 0)
    (nth numbers 4)
    (nth myvec 0)
    (take 2 numbers)
    (take 2 myvec)
    (drop 2 numbers)
    (drop 2 myvec)
    (take 2 mymap)
    (drop 2 mymap)


    ;; Clojure predefined higher-order functions (return sequences)
    (map (fn [x] (* x 2)) numbers)
    ;; you can also write this with a function literal:
    (map #(* % 2) numbers)
    (filter odd? myvec)
    (filter #(< % 4) numbers)
    (filter #(not (string? (second %))) mymap)
    (reduce + numbers)
    ;; three arguments for reduce; the second one is used as the starting point
    (reduce conj [] numbers)

CSci 4651 course web site.

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