Data commit

Task/Call-a-function/Clojure/call-a-function-1.clj

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+(defn one []
+  "Function that takes no arguments and returns 1"
+  1)
+
+(one); => 1

Task/Call-a-function/Clojure/call-a-function-10.clj

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+;;You can assign it to a variable:
+
+(def receipt-us (format-receipt "Toilet Paper" 5 format-price-us))
+
+;; Then the variable holds the value
+receipt-us; => "Toilet Paper $5"
+
+;; Or you can use it in a call to another function
+
+(defn add-store-name [receipt]
+  "A function to add a footer to the receipt"
+  (str receipt "\n Thanks for shopping at Safeway" ))
+
+;; Calls add-store-name with the result of the format function
+(add-store-name (format-receipt "Toilet Paper" 5 format-price-us)); => "Toilet Paper $5\n Thanks for shopping at Safeway"

Task/Call-a-function/Clojure/call-a-function-11.clj

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+;; They are indistinguishable in Clojure, and you can even override a built in one
+
+;; Using built-in addition
+
+(+ 5 5); => 10
+
+;; Using custom defined addition
+
+(defn ? [a b]
+  "Returns the sum of two numbers"
+  (+ a b))
+
+(? 5 5); => 10
+
+;; Overriding a built in function is possible but not recommended
+
+(defn * [a b] ;; Redefining the multiplication operator
+  "Returns the sum of two numbers"
+  (+ a b))
+
+(* 5 5); => 10

Task/Call-a-function/Clojure/call-a-function-12.clj

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+;; They are the same thing - indeed, everything in clojure is a function
+;; Functions without return values simply return nil
+
+(defn no-return-value [a]
+  (print (str "Your argument was" a "; now returning nil")))
+
+(no-return-value "hi"); => nil

Task/Call-a-function/Clojure/call-a-function-13.clj

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+;; Set up a variable that we will pass to a function
+(def the-queen {:name "Elizabeth"
+                :title "Your Majesty"
+                :address "Buckingham Palace"
+                :pets ["Corgi" "Horse"]})
+
+;; A function to modify the data
+(defn adopt-pet [person pet]
+  "Adds pet to the person's list of pets"
+  (update person
+          :pets
+          #(conj % pet)))
+
+;; Calling the function returns a new data structure with the modified pets
+(adopt-pet the-queen "Ferret"); => {:name "Elizabeth":title "Your Majesty" :address "Buckingham Palace" :pets ["Corgi" "Horse" "Ferret]}
+
+;; The original data structure is not changed
+the-queen; => {:name "Elizabeth" :title "Your Majesty" :address "Buckingham Palace" :pets ["Corgi" "Horse"]}

Task/Call-a-function/Clojure/call-a-function-14.clj

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+(defn apply-discount [discount-percentage price]
+  "Function to apply a discount to a price"
+  (-> price
+      (* (- 100 discount-percentage)) ;; Apply discount
+      (/ 100.0)))
+
+;; Here we have assigned the variable to a partial function
+;; It means 'call apply-discount with 10 as the first argument'
+(def discount-10pc-option-1 (partial apply-discount 10))
+
+;; And is equivalent to this:
+(defn discount-10pc-option-2 [price]
+  (apply-discount 10 price))
+
+(discount-10pc-option-1 100); => 90
+
+(discount-10pc-option-2 100); => 90

Task/Call-a-function/Clojure/call-a-function-2.clj

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+(defn total-cost [item-price num-items]
+  "Returns the total price to buy the given number of items"
+  (* item-price num-items))
+
+(total-cost 1 5); => 5

Task/Call-a-function/Clojure/call-a-function-3.clj

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+(defn total-cost-with-discount [item-price num-items & [discount-percentage]]
+  "Returns total price to buy the items after discount is applied (if given)"
+  (let [discount (or discount-percentage 0)] ;; Assign discount to either the discount-percentage (if given) or default 0 if not
+    (-> item-price
+        (* num-items) ;; Calculate total cost
+        (* (- 100 discount)) ;; Apply discount
+        (/ 100.0))))
+
+;; Now we can use the function without the optional arguments, and see the same behaviour as our total-cost function
+(total-cost-with-discount 1 5); => 5
+
+;; Or we can add the third parameter to calculate the cost with 20% discount
+(total-cost-with-discount 1 5 20); => 4

Task/Call-a-function/Clojure/call-a-function-4.clj

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+(defn make-address
+  ([city place-name] (str place-name ", " city))
+  ([city street house-number] (str house-number " " street ", " city))
+  ([city street house-number apartment] (str house-number " " street ", Apt. " apartment ", " city)))
+
+;; To call the function you just need to pass whatever arguments you are supplying as you would with a fixed number
+
+;; First case- the queen doesn't need a street name
+(make-address "London" "Buckingham Palace"); => "Buckingham Palace, London"
+
+;; Second case
+(make-address "London" "Downing Street" 10); => "10 Downing Street, London"
+
+;; Third case
+(make-address "London" "Baker Street" 221 "B"); => "221 Baker Street, Apt. B, London"

Task/Call-a-function/Clojure/call-a-function-5.clj

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+(defn make-mailing-label [{:keys [name address country]}]
+  "Returns the correct text to mail a letter to the addressee"
+  (str name "\n" address "\n" (or country "UK"))) ;; If country is nil, assume it is the UK
+
+;; We can call it with all three arguments in a map to get mickey's international address
+(make-mailing-label {:name "Mickey Mouse"
+                     :address "1 Disney Avenue, Los Angeles"
+                     :country "USA"}); => "Mickey Mouse\n1 Disney Avenue, Los Angeles\nUSA"
+
+;; Or we can call it with fewer arguments for domestic mail
+(make-mailing-label {:name "Her Majesty"
+                     :address "Buckingham Palace, London"}); => "Her Majesty\nBuckingham Palace, London\nUK"

Task/Call-a-function/Clojure/call-a-function-6.clj

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+(defn multiply-by-10 [number]
+  (* 10 number))
+
+(def fifty (multiply-by-10 5))
+
+fifty; => 50

Task/Call-a-function/Clojure/call-a-function-7.clj

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+(defn make-discount-function [discount-percent]
+  "Returns a function that takes a price and applies the given discount"
+  (fn [price] (-> price
+                  (* (- 100 discount-percent))
+                  (/ 100.0))))
+
+;; Now we can create a '20% off' function to calculate prices with your discount card
+(def discount-20pc (make-discount-function 20))
+
+;; Use the function to calculate some discount prices
+(discount-20pc 100); => 80
+(discount-20pc 5); => 4
+
+;; Your friend has a better discount card, we can use the same function to create their discount card function
+(def discount-50pc (make-discount-function 50))
+(discount-50pc 100); => 50
+(discount-50pc 5); => 2.5

Task/Call-a-function/Clojure/call-a-function-8.clj

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+;; Continuing on the same example, let's imagine Anna has a 20% discount card and Bill has 50%. Charlie pays full price
+;; We can store their discount functions in a map
+
+(def discount-cards {"Anna" discount-20pc
+                     "Bill" discount-50pc
+                     "Charlie" identity}) ;; Identity returns whatever value was passed to the function (in this case it will be price)
+
+;; Now we can access them by cardholder name in another function
+(defn calculate-discounted-price [price shopper-name]
+  "Applies the correct discount for the person"
+  (let [discount-fn (get discount-cards shopper-name)] ;; Get the right discount function
+    (discount-fn price))) ;; Apply discount function to the price
+
+(calculate-discounted-price 100 "Anna"); => 80
+(calculate-discounted-price 100 "Bill"); => 50
+(calculate-discounted-price 100 "Charlie"); => 100

Task/Call-a-function/Clojure/call-a-function-9.clj

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+;; Here we have two functions to format a price depending on the country
+
+(defn format-price-uk [price]
+  (str "£" price))
+
+(defn format-price-us [price]
+  (str "$" price))
+
+;; And one function that takes a price formatting function as an argument
+
+(defn format-receipt [item-name price price-formatting-function]
+  "Return the item name and price formatted according to the function"
+  (str item-name
+       " "
+       (price-formatting-function price))) ;; Call the format function to get the right representation of the price
+
+(format-receipt "Loo Roll" 5 format-price-uk); => "Loo Roll £5"
+
+(format-receipt "Toilet Paper" 5 format-price-us); => "Toilet Paper $5"