016: Hello World

Using the `str` function to join values together.

Writing our own functions to insert a persons name in between other strings,
using both the normal `fn` function and the `#_` reader macro short form of a
function definition.

src/four_clojure/016_hello_world.clj

@@ -0,0 +1,87 @@
+(ns four-clojure.016-hello-world)
+
+;; #16 Hello World
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; Difficulty:	Elementary
+
+;; Write a function which returns a personalized greeting.
+
+;; (= (__ "Dave") "Hello, Dave!")
+;; (= (__ "Jenn") "Hello, Jenn!")
+;; (= (__ "Rhea") "Hello, Rhea!")
+
+;; Deconstruct the problem
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; Looking for a function that will join values together to form a string.
+
+;; Additionally we need to define a function that inserts a string inside the sentence.  We cannot simply put Hello in front of the name, we need to add an exclamation mark afterwards
+
+
+;; REPL experiments
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; The `str` function will join values and turn them into a string.
+
+;; Joining two strings together is straight forward.
+(str "Hello," "Dave")
+;; => "Hello,Dave"
+
+;; The `str` function does exactly what you specify.  So in the previous example there is no space between the strings that are joined.
+
+;; Spaces need to be explicitly specified
+(str "Hello, " "Dave")
+;; => "Hello, Dave"
+
+;; or you can include spaces separately, depending on which seems more readable.
+
+(str "Hello," " " "Dave")
+;; => "Hello, Dave"
+
+
+
+;; Define a function that takes a persons name and inserts it between Hello, and !
+
+(fn [person-name]
+  (str "Hello, " person-name "!"))
+
+
+;; and call that function definition with a persons name as an argument
+((fn [person-name]
+   (str "Hello, " person-name "!")) "Dave")
+;; => "Hello, Dave!"
+
+
+;; There is a short form for defining a function, using a reader macro.
+
+#(str "I am a function definition using the reader macro")
+
+;; And to call this function definition with an argument it needs to be put inside a list, `()`
+;; Argument are used by placing a percent symbol, `%`, and the argument number within the function definition
+;; `%1` is the first argument passed to the function.  Or you can just use `%`
+
+(#(str %1 ", " "I am a function definition using the reader macro.  I take one argument")
+ "Dave")
+;; => "Dave, I am a function definition using the reader macro.  I take one argument"
+
+;; Applying this short form to the 4Clojure answer we get:
+
+;; using the short form of a function definition
+#(str "Hello, " % "!")
+
+;; and the short form of calling a function
+(#(str "Hello, " % "!")
+ "Mani")
+
+
+
+;; Answers summary
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; The normal form for a function definition is nicely readable
+(fn [person-name]
+  (str "Hello, " person-name "!"))
+
+;; As this funciton is relatively simple, then even the short form is quite readable and succinct
+#(str "Hello, " % "!")