048 Intro to some - some function

A discussion of how to use the some function with predicate functions, lambda
functions and different data sequences.

Also included examples of the `some` function as used in production system.

src/four_clojure/048_intro_to_some.clj

@@ -0,0 +1,115 @@
+(ns four-clojure.048-intro-to-some)
+
+;; #48 Intro to some
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; Difficulty:	Easy
+;; Topics:
+
+;; The some function takes a predicate function and a collection.
+;; It returns the first logical true value of (predicate x) where x is an item in the collection.
+
+;; (= __ (some #{2 7 6} [5 6 7 8]))
+;; (= __ (some #(when (even? %) %) [5 6 7 8]))
+
+
+;; Deconstruct the problem
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; The `some` function is used to see if some value or values are contained within a collection.
+
+;; `some` is often a better choice than what would seem to be the more obvious `contains?` function.
+
+;; REPL experiments
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; Lets experiment with the `some` function
+
+;; Using a predicate function, then if the predicate returns `true` anywhere in the collection,
+;; `true` will be returned
+(some odd? [1 2 3 4 5])
+;; => true
+
+(some even? [1 2 3 4 5])
+;; => true
+
+;; for specific values, we would need to use a lambda function (inline function)
+(some #(= 3 %) [1 2 3 4 5])
+;; => true
+
+
+;; Using a set as a predicate function
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(some #{3} #{1 2 3 4 5})
+;; => 3
+
+
+;; The first value found in both the sets is returned
+(some #{2 7 6} [5 6 7 8])
+;; => 6
+
+;; only the order of the collection is relevant,
+;; not the order of values in the set used as a predicate
+;; each value in the set is tested with the first value in vector
+;; continuing until there is a match or the end of the vector is reached.
+(some #{2 7 6 8} [8 6 7 5])
+;; => 8
+
+
+;; Answers summary
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+6
+
+
+;; production examples
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; A simple production example is to check if a user id is part of a role
+
+;; userid is defined as uuids
+
+;; Generate some UUIDs for user accounts
+
+(java.util.UUID/randomUUID)
+;; => #uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"
+;; => #uuid "85dddefd-58a7-401b-a5da-b0fa7070047e"
+
+;; Put the account ids into a set and define a name
+(def admin-set
+  #{#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"
+    #uuid "85dddefd-58a7-401b-a5da-b0fa7070047e"})
+
+;; or we can also use a vector
+(def admin-vector
+  [#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"
+   #uuid "85dddefd-58a7-401b-a5da-b0fa7070047e"])
+
+;; we can see if a userid is in the admin set using the `some` function
+(some #{#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"} admin-set)
+;; => #uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"
+
+;; If the userid is in the admin set, it returns the uuid.
+;; so we can check if the return value is a uuid type.
+(uuid?
+ (some #{#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"} admin-set))
+;; => true
+
+;; and the same works for a vector
+(some #{#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"} admin-vector)
+;; => #uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"
+
+(uuid?
+ (some #{#uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546"} admin-vector))
+;; => true
+
+;; using a simple lambda function we can create a predicate
+;; to test if a specific userid is part of the set
+(some #(= #uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546" %)
+      admin-set)
+;; => true
+
+(some #(= #uuid "db2ad2a0-a046-4366-a7e6-b9b16010c546" %)
+      admin-vector)
+;; => true