Clojourney

Repo where I'll document and share my advancements in learning

• Clojourney
  • Language concepts
    • Lists
    • Vectors
      • Additional resources
  • Exercism exercises
    • Two-fer
      • Iteration #0
      • Iteration #1
    • Reverse-string
      • Iteration #0
      • Iteration #1
      • Iteration #2
      • Iteration #3
      • Iteration #4
      • Iteration #5
      • Iteration #6
      • Iteration #7
      • Iteration #8
      • Iteration #9
      • Iteration #10
      • Iteration #11
      • Iteration 12
    • Accumulate
      • Iteration #0
    • Beer-song
      • Iteration #0

Language concepts

Lists

• Are singly-linked-lists;

Vectors

• Support fast indexed access;

Additional resources

• https://hypirion.com/musings/understanding-persistent-vector-pt-1

Exercism exercises

Resource where I'll post the iterations of exercism Clojure track exercises (mostly based on feedback by code mentors, to whom I'm grateful).

Two-fer

Iteration #0

(ns two-fer)

(defn two-fer
  ([] "One for you, one for me.)
  ([name] (str "One for " name  ", one for me.")))

Iteration #1

(ns two-fer)

(defn two-fer
  ([] (two-fer "you")) ; define diffferent arities to simulate "default arguments"
  ([name] (str "One for " name  ", one for me.")))

Reverse-string

Iteration #0

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map (fn [idx] (str (get s (- (- (count s) 1) idx))))
               (range (count s)))))

Iteration #1

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map (fn [idx] (str (get s idx)))
               (range (count s) -1 -1)))) ; use begin, end and step params

Iteration #2

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map (fn [idx] (str (nth s idx))) ; change `get` for `nth`
               (range (- (count s) 1) -1 -1))))

Iteration #3

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map (fn [idx] (str (nth s idx)))
               (range (dec (count s)) -1 -1)))); change (- x 1) for (dec x)

Iteration #4

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map #(str (nth s %)) ; change anonymous function for reader syntax
               (range (dec (count s)) -1 -1))))

Iteration #5

(ns reverse-string)

(defn reverse-string [s]
  (reduce str
          (map #(nth s %) ; remove call to `str` from mapping fn
               (range (dec (count s)) -1 -1))))

Iteration #6

(ns reverse-string)

(defn reverse-string [s]
  (apply str ; no need to reduce, can apply str to compact list of chars
         (map #(nth s %)
              (range (dec (count s)) -1 -1))))

Iteration #7

(ns reverse-string)

(defn reverse-string [s]
  (apply str
         (loop [s_ s ; create general reverse ; without depending on String random access
                reversed []]
           (if (empty? s_)
             reversed
             (recur (drop-last s_) (conj reversed (last s_)))))))

Iteration #8

(ns reverse-string)

(defn reverse-string [s]
  (apply str 
         (loop [s_ s
                reversed ()]
           (if (empty? s_)
             reversed
            (recur (rest s_) (conj reversed (first s_))))))) ; without using `last`, `drop-last`, and vectors (N^2)

Iteration #9

(ns reverse-string)

(defn reverse-string [s]
  (apply str (reduce #(conj %1 %2) () s))) ; using reduce instead

Iteration #10

(ns reverse-string)

(defn reverse-string [s]
  (apply str (reduce conj () s))) ; #(conj %1 %2) is the own definition of `conj` ;-)

Iteration #11

(ns reverse-string)

(defn reverse-string [s]
  (apply str (into () s))) ; see `(source into)` to see that this is would fall unto the condition `(reduce conj to from)`

Iteration 12

(ns reverse-string)

(defn reverse-string [s]
  (.toString (.reverse (StringBuilder. ^String s)))) ; using Java interops -> probably over engineering in most cases (this is what is implemented by `clojure.string/reverse`

Accumulate

Iteration #0

(ns accumulate)

(defn accumulate [fn_ list_]
  (map fn_ list_)
  )

Beer-song

Iteration #0

(ns beer-song)

(defn bottles-in-wall [expression]
  (str expression " of beer on the wall"))

(defn base-verse [args]
  (str (bottles-in-wall (nth args 0)) ", " (nth args 1) " of beer.\n"
       "Take " (nth args 2) " down and pass it around, " (bottles-in-wall (nth args 3)) ".\n"))

(defn singular
  "Return the singular verse of the song"
  ([] ["1 bottle" "1 bottle" "it" "no more bottles"]))

(defn is-one? [num_] (= num_ 1))

(defn bottle-expression [num_]
  (if (is-one? num_)
    (str num_ " bottle")
    (str num_ " bottles")))

(defn plural
  "Return a plural verse of the song"
  ([num_]  [(bottle-expression num_) (bottle-expression num_) "one" (bottle-expression (dec num_))]))

(defn in-stock [num_]
  (if (is-one? num_)
    (base-verse (singular))
    (base-verse (plural num_))))

(defn out-of-stock
  ([] (str "No more bottles of beer on the wall, no more bottles of beer.\n"
           "Go to the store and buy some more, 99 bottles of beer on the wall.\n")))

(defn is-zero? [num_] (= num_ 0))

(defn verse
  ([num_]
   (if (is-zero? num_)
     (out-of-stock)
     (in-stock num_))))

(defn sing
  ([start] (sing start 0))
  ([start end] (apply str (drop-last (apply str  (map #(str % "\n") (map verse (range start (dec end) -1)))))))) ; drop last \n due to test case