From d9fbc9bdb63cbf058fdf4a8eca33e74e53206c71 Mon Sep 17 00:00:00 2001
From: ajet <ajeniski4@gmail.com>
Date: Mon, 14 Sep 2026 07:26:40 -0900
Subject: [PATCH] add clj examples

---
 learnclj.clj | 334 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 334 insertions(+)
 create mode 100644 learnclj.clj

diff --git a/learnclj.clj b/learnclj.clj
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+;; ============================================
+;; learnclj.clj — Clojure Learning Examples
+;; ============================================
+(ns learnclj
+  (:require [clojure.string :as str]))
+
+;; --- 1. Basics ---
+
+;; Literals
+123          ; => 123 (Integer)
+3.14         ; => 3.14 (Double)
+22/7         ; => 22/7 (Ratio/rational)
+:keyword     ; => :keyword (Keyword)
+"string"     ; => "string" (String)
+\c           ; => \c (Character)
+true         ; => true (Boolean)
+nil          ; => nil (Null/Nothing)
+
+;; --- 2. Defining Values & Functions ---
+
+;; def — binds a name to a value in the namespace
+(def π 3.14159265)
+
+;; defn — defines a function
+(defn greet [name]
+  (str "Hello, " name "!"))
+(greet "Sam") ;; => "Hello, Sam!"
+
+;; Anonymous function
+(#(+ %1 %2) 3 4)        ; => 7
+(fn [x y] (+ x y))      ; => #object[clojure.core$fn__... 0x... "fn..."] (anonymous function)
+
+;; Function with default arguments
+(defn greet-default [name {:keys [formal] :or {formal false}}]
+  (if formal
+    (str "Good day, " name)
+    (str "Hey, " name)))
+(greet-default "Sam" {})   ; => "Hey, Sam"
+(greet-default "Sam" {:formal true}) ; => "Good day, Sam"
+
+;; Variadic function
+(defn sum [& numbers]
+  (reduce + 0 numbers))
+(sum 1 2 3 4)           ; => 10
+
+;; --- 3. Data Structures ---
+
+;; Lists — linked lists, quoted for data
+'(1 2 3)          ; => (1 2 3) (quoted list)
+(list 1 2 3)       ; => (1 2 3)
+
+;; Vectors — indexed, sequential
+[1 2 3]            ; => [1 2 3]
+(vector "a" "b" "c") ; => ["a" "b" "c"]
+(get [10 20 30] 1)     ; => 20
+
+;; Maps — key-value pairs
+{:name "Alice" :age 30}   ; => {:name "Alice", :age 30}
+{"x" 1 "y" 2}            ; => {"x" 1, "y" 2}
+(get {:a 1 :b 2} :a)   ; => 1
+(:name {:name "Alice"}) ; => "Alice" (keyword as accessor)
+
+;; Sets — unique values
+#{1 2 3 4 5}        ; => #{1 2 3 4 5} (order not guaranteed)
+(set [1 2 2 3 3 3])    ; => #{1 2 3} (duplicates removed, order not guaranteed)
+
+;; --- 4. Control Flow ---
+
+;; if
+(if (> 5 3)
+  "yes"
+  "no")           ; => "yes"
+
+;; when — like if but for side effects (no else branch)
+(when true
+  (print "Side effect here")
+  :result)         ; => :result
+
+;; cond — multiple conditions
+(cond
+  (= 1 1) "one"
+  (= 2 2) "two"
+  :else "other")   ; => "one"
+
+;; case — exact match dispatch
+(case 2
+  1 "one"
+  2 "two"
+  3 "three"
+  "other")         ; => "two"
+
+;; and / or — short-circuiting
+(and true false nil)   ; => false (returns first falsy value)
+(or false true 42)     ; => true
+
+;; --- 5. Sequences ---
+
+;; map — apply function to each element
+(map inc [1 2 3])           ; => (2 3 4)
+(map str ["a" "b"] [1 2])  ; => ("a1" "b2")
+
+;; filter
+(filter even? [1 2 3 4 5]) ; => (2 4)
+
+;; reduce
+(reduce + [1 2 3 4])       ; => 10
+(reduce str ["a" "b" "c"]) ; => "abc"
+
+;; into — combine collections
+(into [] (map inc [1 2 3]))   ; => [2 3 4]
+(into {} (map #(vector %1 %2) [:a :b] [1 2])) ; => {:a 1, :b 2}
+
+;; sequence processing
+(sequence (comp
+            (filter odd?)
+            (map #(* % %)))
+          [1 2 3 4 5 6 7])  ; => (1 9 25 49)
+
+;; --- 6. Destructuring ---
+
+;; Vector destructuring
+(let [[first second & rest] [1 2 3 4 5]]
+  [first second rest])
+; => [1 2 (3 4 5)]
+
+;; Map destructuring
+(let [{name :name age :age} {:name "Bob" :age 25}]
+  [name age])
+; => ["Bob" 25]
+
+;; Nested destructuring
+(let [{:keys [x y] :as point} {:point {:x 10 :y 20}}
+      {:keys [x y]} (:point point)]
+  [x y])
+; => [10 20]
+
+;; Function parameter destructuring
+(defn show-point [{:keys [x y] :or {x 0 y 0}}]
+  (str "Point: (" x ", " y ")"))
+(show-point {:x 10 :y 20}) ; => "Point: (10, 20)"
+(show-point {})             ; => "Point: (0, 0)"
+
+;; --- 7. Namespaces ---
+
+;; require — load a namespace
+;; (require '[clojure.string :as str])
+;; (str/upper-case "hello")
+
+;; use — import functions directly
+;; (use '[clojure.string :only [upper-case]])
+;; (upper-case "hello")
+
+;; import — Java classes
+;; (import java.util.Date)
+;; (Date.)
+
+;; --- 8. Recursion & Tail Recursion ---
+
+;; Regular recursion
+(defn factorial [n]
+  (if (<= n 1)
+    1
+    (* n (factorial (dec n)))))
+
+;; Tail-recursive with loop/recur
+(defn factorial-tail [n]
+  (loop [n n acc 1]
+    (if (<= n 1)
+      acc
+      (recur (dec n) (* acc n)))))
+
+;; --- 9. Conditionals with when-let / if-let ---
+
+;; when-let — bind and condition in one
+(when-let [val (get {:a 1} :b)]
+  val)  ; => nil (doesn't evaluate body)
+
+(if-let [val (get {:a 1} :a)]
+  val
+  "not found")  ; => 1
+
+;; --- 10. Multiline strings & syntax quoting ---
+
+;; Multiline string
+(def multiline
+  "This is a
+   multiline
+   string")
+
+;; Syntax quoting (backquote) — auto-qualifies vars
+(defn make-list []
+  `(~"a" ~"b" "c"))  ; => ("a" "b" "c")
+
+;; --- 11. Protocols (OOP-like) ---
+
+(defprotocol Shape
+  (area [this])
+  (perimeter [this]))
+
+(deftype Rectangle [width height]
+  Shape
+  (area [this] (* width height))
+  (perimeter [this] (* 2 (+ width height))))
+
+(defn make-rectangle [w h]
+  (Rectangle. w h))
+
+(make-rectangle 4 5)       ; => #object[learnclj.Rectangle ...]
+(area (make-rectangle 4 5))      ; => 20
+(perimeter (make-rectangle 4 5)) ; => 18
+
+;; --- 12. Records ---
+
+(defrecord Person [name age email])
+
+(def alice (->Person "Alice" 30 "alice@example.com"))
+(:name alice)           ; => "Alice"
+(->Person "Alice" 30 "alice@example.com")  ; => #learnclj.Person{:name "Alice", :age 30, :email "alice@example.com"}
+(map->Person {:name "Bob" :age 25 :email "bob@example.com"}) ; => #learnclj.Person{:name "Bob", :age 25, :email "bob@example.com"}
+
+;; --- 12b. Type & Protocol Extension ---
+
+;; Protocol to define
+(defprotocol Formattable
+  (format-for-display [this] "Returns a formatted string representation"))
+
+;; extend-type — add protocol methods to an existing type
+(extend-type Number
+  Formattable
+  (format-for-display [this]
+    (if (integer? this)
+      (str "Int: " this)
+      (str "Num: " this))))
+
+(format-for-display 42)      ; => "Int: 42"
+(format-for-display 3.14)    ; => "Num: 3.14"
+
+;; extend-protocol — add protocol methods to multiple types at once
+(extend-protocol Formattable
+  java.util.Date
+  (format-for-display [this]
+    (str "[Date] " (.toString this)))
+
+  java.util.Calendar
+  (format-for-display [this]
+    (str "[Calendar] " (.getTime this)))
+
+  java.util.UUID
+  (format-for-display [this]
+    (str "[UUID] " (.toString this))))
+
+(format-for-display (java.util.Date.))       ; => "[Date] ..."
+(format-for-display (java.util.UUID/randomUUID)) ; => "[UUID] ..."
+
+;; --- 13. Atoms & State ---
+
+(def counter (atom 0))
+
+(swap! counter inc)     ; => 1
+(swap! counter + 5)     ; => 6
+(dosync
+  (reset! counter 0))   ; => 0
+
+;; --- 14. Java Interop ---
+
+;; Method call
+(.toUpperCase "hello")   ; => "HELLO"
+(.substring "hello" 1 3) ; => "el"
+(. "hello" length)       ; => 5
+(.length "hello")        ; => 5
+(.age alice)              ; => 30
+(.. alice email toUpperCase) ; => "ALICE@EXAMPLE.COM"
+
+;; Static method
+(System/getProperty "user.name")  ; => "ajet"
+
+;; Constructor
+(java.util.Date.)  ; => #inst "2026-09-14T..." (current date/time)
+
+;; --- 15. Threading Macros ---
+
+;; Thread-first (->) — passes result as first arg
+(-> "hello"
+    (.toUpperCase)
+    (.replace "H" "J")
+    (.toLowerCase))  ; => "jello"
+
+;; Thread-last (->>) — passes result as last arg
+(->> [1 2 3 4 5]
+     (filter odd?)
+     (map #(* % %))
+     (reduce +))   ; => 35
+
+;; --- 16. Error Handling ---
+
+;; try/catch
+(try
+  (/ 1 0)
+  (catch ArithmeticException e
+    (str "Math error: " (.getMessage e))))  ; => "Math error: Divide by zero"
+
+;; assert — throws AssertionError on failure
+(assert (= 2 (+ 1 1)))  ; => nil (assert returns nil on success)
+;; (assert (= 1 2) "custom message") ; would throw with custom message
+
+;; --- 17. Macros (simplified) ---
+
+;; Define a simple macro
+(defmacro unless [pred & body]
+  `(if (not ~pred)
+     ~@body))
+
+(unless true
+  (print "Won't print")
+  "result")  ; => "result"
+
+;; --- 18. Common Patterns ---
+
+;; Compose functions
+(defn make-upper [s] (str/upper-case s))
+(def make-upper-lower (comp str/lower-case str/upper-case))  ; => #object[clojure.core$comp$fn ...]
+
+;; Partial application
+
+;; Partial application
+(def add-5 (partial + 5))
+(add-5 3)  ; => 8
+
+;; Complement — negate a predicate
+(every-pred (complement nil?) (complement zero?))  ; => #object[clojure.core$every_pred ...]
+
+;; Juxt — create multiple functions
+(def j (juxt :x :y))   ; => #object[clojure.core$juxt ...]
+(j {:x 1 :y 2})  ; => [1 2]