diff --git a/.gitignore b/.gitignore
index a797815..c2c8eb1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 !.gitignore
 build*
 cmake*
+demo_*
 dist/
 lib/*.so
 out/
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 29ce659..8dba824 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.16)
-project(fun VERSION 0.13.0 LANGUAGES C)
+project(fun VERSION 0.13.1 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 11)
 set(CMAKE_C_STANDARD_REQUIRED ON)
diff --git a/demo.fun b/demo.fun
new file mode 100644
index 0000000..b6d5b03
--- /dev/null
+++ b/demo.fun
@@ -0,0 +1,188 @@
+#!/usr/bin/env fun
+
+// Fun Interactive Demo
+// Run: FUN_LIB_DIR="$(pwd)/lib" ./build/fun demo.fun   (Linux/macOS/FreeBSD)
+//      $env:FUN_LIB_DIR="$PWD\lib"; .\build\fun.exe demo.fun  (Windows PowerShell)
+
+// Use a stdlib helper from the repository (fallback to ./lib via preprocessor)
+#include <utils/math.fun>
+
+print("")
+print("=== Fun Interactive Demo ===")
+
+print("")
+print("== Basics: dynamic vs typed variables and typeof ==")
+x = 123
+print("x=" + to_string(x) + " typeof=" + typeof(x))
+x = "hello"
+print("x=" + to_string(x) + " typeof=" + typeof(x))
+
+number n = 42
+print("n=" + to_string(n) + " typeof=" + typeof(n))
+n = n + 8
+print("n=" + to_string(n) + " typeof=" + typeof(n))
+// Uncomment to see a runtime type error and halt the program:
+// n = "oops"
+
+boolean flag = 0
+print("flag=" + to_string(flag) + " typeof=" + typeof(flag))
+flag = 2     // gets clamped to 1
+print("flag(after clamp 2)=" + to_string(flag))
+
+int8 si = 130     // clamps to 127
+uint8 u8 = 300    // clamps to 255
+print("int8 si=" + to_string(si) + ", uint8 u8=" + to_string(u8))
+
+nil nothing = nil
+print("nothing typeof=" + typeof(nothing))
+
+print("")
+print("== Arithmetic, comparisons, and logic ==")
+print("3+4=" + to_string(3 + 4))
+print("10-3=" + to_string(10 - 3))
+print("6*7=" + to_string(6 * 7))
+print("20/3=" + to_string(20 / 3))
+print("20%3=" + to_string(20 % 3))
+print("2<3=" + to_string(2 < 3) + ", 3<=3=" + to_string(3 <= 3))
+print("5>2=" + to_string(5 > 2) + ", 2>=2=" + to_string(2 >= 2))
+print("2==2=" + to_string(2 == 2) + ", 2!=3=" + to_string(2 != 3))
+print("(1 && 0)=" + to_string(1 && 0) + ", (0 || 1)=" + to_string(0 || 1) + ", !0=" + to_string(!0))
+
+print("")
+print("== Strings and arrays ==")
+s = "alpha,beta,gamma"
+parts = split(s, ",")
+print("split -> len=" + to_string(len(parts)))
+print("join(parts,'|')=" + join(parts, "|"))
+print("substr('abcdef', 2, 3)=" + substr("abcdef", 2, 3))
+print("find('hello world','world')=" + to_string(find("hello world", "world")))
+
+arr = [1, 2, 3]
+print("arr len=" + to_string(len(arr)))
+push(arr, 4)
+print("after push 4 -> len=" + to_string(len(arr)))
+v = pop(arr)
+print("popped=" + to_string(v) + " len=" + to_string(len(arr)))
+insert(arr, 1, 99)  // [1,99,2,3]
+print("after insert(1,99) arr[1]=" + to_string(arr[1]))
+set(arr, 2, 55)     // [1,99,55,3]
+print("after set(2,55) arr[2]=" + to_string(arr[2]))
+print("contains(arr, 55)=" + to_string(contains(arr, 55)) + ", indexOf(arr, 99)=" + to_string(indexOf(arr, 99)))
+print("slice arr[1:3] len=" + to_string(len(arr[1:3])))
+print("join(arr, ',')=" + join(arr, ","))
+
+print("")
+print("== Enumerate and zip ==")
+for p in enumerate(["a", "b", "c"])
+  print("idx=" + to_string(p[0]) + " val=" + to_string(p[1]))
+z = zip([1, 2], ["x", "y"])
+for pair in z
+  print("(" + to_string(pair[0]) + "," + to_string(pair[1]) + ")")
+
+print("")
+print("== Maps (dictionaries) ==")
+m = {"name": "Alice", "age": 30}
+print("has(m,'age')=" + to_string(has(m, "age")))
+print("m['name']=" + to_string(m["name"]))
+m.age = 31
+print("m.age after = " + to_string(m.age))
+print("keys: " + join(keys(m), ","))
+print("values count=" + to_string(len(values(m))))
+
+print("")
+print("== Functions and higher-order ops (map/filter/reduce) ==")
+fun greet(name)
+  print("Hello, " + to_string(name) + "!")
+greet("Fun")
+
+fun double(x)
+  return x * 2
+
+nums = [1, 2, 3, 4, 5]
+twice = map(nums, double)
+print("len(map)=" + to_string(len(twice)) + " first=" + to_string(twice[0]))
+
+fun isEven(x)
+  return (x % 2) == 0
+evens = filter(nums, isEven)
+print("filter evens len=" + to_string(len(evens)))
+
+fun sum(acc, x)
+  return acc + x
+total = reduce(nums, 0, sum)
+print("reduce sum=" + to_string(total))
+
+print("")
+print("== If / else-if / else and loops ==")
+val = 7
+if (val < 0)
+  print("neg")
+else if (val == 0)
+  print("zero")
+else
+  print("pos")
+
+print("for range(0, 5):")
+for i in range(0, 5)
+  print(i)
+
+print("for in array:")
+for x in ["h", "i", "!"]
+  print(x)
+
+print("while loop (count to 3):")
+c = 0
+while (c < 3)
+  print(c)
+  c = c + 1
+
+print("")
+print("== Classes (with 'this' and methods) ==")
+class Person(string name, number age)
+  // default field values (can be overridden by constructor params)
+  full = name + " (" + to_string(age) + ")"
+
+  // required: first param is 'this'
+  fun say(this)
+    print("I am " + to_string(this.full))
+
+  // typeof(instance) will return this string for Maps tagged with __class
+  fun toString(this)
+    return "Person"
+
+p = Person("Alice", 30)
+p.say()
+print("typeof p: " + typeof(p))
+
+print("")
+print("== Math and bitwise helpers ==")
+print("min(3,9)=" + to_string(min(3, 9)) + ", max(3,9)=" + to_string(max(3, 9)))
+print("clamp(15,0,10)=" + to_string(clamp(15, 0, 10)) + ", abs(-5)=" + to_string(abs(-5)))
+print("pow(2,10)=" + to_string(pow(2, 10)))
+print("band(0xF0,0x3C)=" + to_string(band(0xF0, 0x3C)))
+print("bor(0x0F,0x30)=" + to_string(bor(0x0F, 0x30)))
+print("bxor(0xFF,0x0F)=" + to_string(bxor(0xFF, 0x0F)))
+print("bnot(0x0F)=" + to_string(bnot(0x0F)))
+print("shl(1,4)=" + to_string(shl(1, 4)) + ", shr(128,3)=" + to_string(shr(128, 3)))
+print("rol(0x12,1)=" + to_string(rol(0x12, 1)) + ", ror(0x12,1)=" + to_string(ror(0x12, 1)))
+
+print("")
+print("== Random numbers ==")
+random(12345)  // seed
+print("randomInt(1,10) -> " + to_string(randomInt(1, 10)))
+
+print("")
+print("== File IO and environment ==")
+write_ok = write_file("demo_tmp.txt", "Hello from Fun!\n")
+print("write_file ok=" + to_string(write_ok))
+content = read_file("demo_tmp.txt")
+print("read_file len=" + to_string(len(content)))
+print("PATH starts with: " + substr(env("PATH"), 0, 24))
+
+print("")
+print("== Library include demo ==")
+print("add(2,3) from utils/math.fun -> " + to_string(add(2, 3)))
+print("times(4,5) from utils/math.fun -> " + to_string(times(4, 5)))
+
+print("")
+print("=== Demo complete. Have Fun! ===")