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+# Fun Language Specification v0.3
+
+This document describes Fun (Fun Uses Nothing) as of version 0.3. It supersedes v0.2 by formalizing classes/objects, inheritance, namespaced includes, richer collections and builtins, concurrency primitives, networking and OS integration, as reflected by the examples.
+
+---
+
+## 1) Overview and Goals
+
+- Readable: strict, indentation-based syntax (2 spaces), no semicolons.
+- Safe: explicit types, no implicit numeric coercions, bounds-checked operations, controlled side effects.
+- Hackable: pragmatic stdlib, process I/O, sockets, threads.
+
+What’s new in v0.3 (high level):
+- Classes and objects with methods, constructors, and inheritance (`extends`).
+- Dot-call sugar for method calls, and explicit `this` in method definitions.
+- Namespaced `#include ... as alias` for module imports.
+- Maps (dictionaries) with literals and helpers.
+- Control-flow additions: `break` and `continue`.
+- Threads: `thread_spawn`, `thread_join` and `sleep`.
+- Expanded system and network APIs (TCP/Unix sockets, serial, env, timers).
+- Bitwise helpers (`band`, `bor`, `bxor`, `bnot`, `shl`).
+- Exception syntax (`try/catch/finally`) is defined; runtime throwing/handling may be partial.
+
+---
+
+## 2) Lexical Structure
+
+- Case-sensitive identifiers: letters, digits, `_`; must not start with a digit.
+- Comments:
+  - Single-line: `// comment`
+  - Multi-line: `/* ... */`
+- Whitespace and newlines:
+  - Indentation is exactly 2 spaces; tabs are forbidden.
+  - Newline terminates statements; no semicolons.
+
+Reserved keywords (cannot be redefined):
+- `if`, `else`, `for`, `while`, `break`, `continue`
+- `fun`, `return`
+- `class`, `extends`
+- `global`, `private`
+- `true`, `false`
+- `try`, `catch`, `finally`
+
+Notes:
+- `#include` is a directive, not an expression; `as` is part of the include alias syntax (see Modules & Includes).
+
+---
+
+## 3) Types
+
+Scalar types:
+- `number`: 64-bit signed integer.
+- `float`: 64-bit IEEE-754 floating point.
+- `string`
+- `boolean`: `true` / `false` (in conditionals `0` and `1` are accepted where noted).
+- `byte`: 8-bit value (see conversions and overflow rules).
+
+Fixed-width integers (signed/unsigned):
+- `int8`, `uint8`, `int16`, `uint16`, `int32`, `uint32`, `int64`, `uint64`
+
+Aggregate types:
+- `array` and typed arrays: `array<T>`
+- `map<K, V>` (dictionary / associative array)
+- `object` (instances of `class`)
+
+Examples:
+```fun
+number n = 42
+float pi = 3.14159
+string s = 'He said: "Fun!"'
+boolean ok = true
+byte b = 0x41
+
+array<number> nums = [1, 2, 3]
+array mixed = [1, "two", true, [3, 4]]
+
+m = { "a": 1, "b": 2 }  // map<string, number>
+```
+
+Dynamic typing escape hatch (discouraged; use when interacting with unknown data):
+```fun
+dynamic string x = 42   // allowed by spec; runtime performs dynamic checks
+x = "Now I'm a string"
+```
+
+---
+
+## 4) Variables and Scope
+
+- `global` variables are visible program-wide.
+- `private` variables are file-local (module private).
+- Rebinding a global or shadowing a name is a compile-time error.
+
+```fun
+global string message = "Hello"
+private number count = 42
+number local = 23
+```
+
+---
+
+## 5) Operators and Builtins
+
+Arithmetic: `+`, `-`, `*`, `/`, `%`
+
+Comparison: `==`, `!=`, `>`, `<`, `>=`, `<=`
+
+Boolean: `&&`, `||`, `!`
+
+Assignment: `=`
+
+Bitwise helpers (functions):
+- `band(a, b)`, `bor(a, b)`, `bxor(a, b)`, `bnot(a)`, `shl(a, n)`
+
+```fun
+print(bxor(0x80000000, 0x00000001))  // 2147483649
+print(shl(0x80, 24))                 // 2147483648
+```
+
+Collection helpers (selected):
+- Arrays: `push(arr, v)`, `join(arr, sep)`, `map(arr, f)`, `filter(arr, pred)`, `reduce(arr, init, f)`
+- Maps: `has(m, key)`, `keys(m)`, `values(m)`
+
+Type/convert helpers (selected):
+- `typeof(x) -> string`
+- `to_string(x)` and numeric casts (see examples for `cast_demo.fun` and `conversions_showcase.fun`)
+
+---
+
+## 6) Control Flow
+
+If/Else:
+```fun
+if (x != y)
+  print(x)
+else if (a == b || h != i)
+  print(a + b)
+else
+  if (k < 1 && l > 1)
+    print("Buh!")
+```
+
+While:
+```fun
+number i = 0
+while i < 10
+  if i % 2 == 0
+    i = i + 1
+    continue
+  if i > 5
+    break
+  i = i + 1
+```
+
+For:
+- Range iteration: `for i in range(start, end)`
+- Array iteration: `for x in arr`
+- Map iteration: `for k in keys(m)` then `m[k]`
+
+```fun
+for i in range(0, 5)
+  print(i)
+
+for x in [1, 2, 3]
+  print(x)
+```
+
+Loop control:
+- `break` exits the innermost loop.
+- `continue` skips to next iteration of the current loop.
+
+Try/Catch/Finally (syntax defined; runtime throwing may be incomplete):
+```fun
+try
+  // protected section
+  risky()
+catch err
+  print("caught error:")
+  print(err)
+finally
+  print("cleanup")
+```
+
+---
+
+## 7) Functions
+
+Built-in/runtime functions (selected):
+- Basic: `print(x)`, `range(a, b)`, `sleep(ms)`
+- Processes: `exec(cmd) -> string`, `system(cmd) -> number`
+- Async processes: `nexec(cmd) -> pid/object`, `nsystem(cmd) -> number`, `nspawn(cmd) -> pid`, `wait(pid)`, `read(pid)`, `kill(pid)`
+- Threads: `thread_spawn(fn, argOrArgs) -> thread_id`, `thread_join(thread_id) -> any`
+
+User-defined functions:
+```fun
+fun add(a, b)
+  return a + b
+
+fun divide(a, b)
+  if b == 0
+    return 0, "division by zero"
+  return a / b, ""
+```
+
+Higher-order helper (example pattern):
+```fun
+fun call(f, arg)
+  return f(arg)
+```
+
+Multiple return values are supported syntactically; use tuple-like unpacking via arrays as needed in user code patterns.
+
+---
+
+## 8) Classes and Objects
+
+Definition:
+```fun
+class Name(/* optional ctor params with types */)
+  // field defaults
+  field1 = 0
+  field2 = ""
+
+  // method: first parameter must be `this`
+  fun method(this, arg1, arg2)
+    // ...
+    return 0
+```
+
+Constructors:
+- Default constructor maps the class header parameters to fields of the same names.
+- Optional explicit constructor hook: define `fun _construct(this, ...params...)` to customize initialization. It is invoked automatically on instantiation.
+
+Fields and methods:
+- Fields are created/initialized with simple assignments in the class body.
+- Methods are functions declared inside the class; the first parameter must be `this`.
+- Private members: any field or method whose name starts with `_` is considered private to the class. Accessing them from outside should raise an access error.
+
+Instantiation and method calls:
+```fun
+p = Point(10, -2)
+print(p.x)            // field access via `.` or indexing
+print(p["x"])         // map-like field access is supported
+
+// Dot-call sugar: p.method(a, b) is equivalent to method(p, a, b)
+print(p.toString())
+```
+
+Method references:
+```fun
+move_fn = p["move"]
+move_fn(p, 3, 5)  // call with explicit `this`
+```
+
+Inheritance:
+```fun
+class Parent(number start)
+  value = 0
+  fun _construct(this, s)
+    this.value = s
+
+  fun describe(this)
+    return "Parent(value=" + to_string(this.value) + ")"
+
+class Child(number start) extends Parent
+  bonus = 5
+  fun _construct(this, s)
+    // runs after parent fields merged
+    this.value = this.value + this.bonus
+  fun describe(this)
+    return "Child(value=" + to_string(this.value) + ", bonus=" + to_string(this.bonus) + ")"
+```
+
+`typeof` on classes and instances:
+- `typeof(Point) == "Class"`
+- `typeof(p) == "Point(10, -2)"` (implementation-specific descriptive form)
+
+---
+
+## 9) Modules and Includes
+
+Include sources:
+- System/stdlib: angle brackets search the Fun library path (e.g., `FUN_LIB_DIR`).
+  ```fun
+  #include <utils/math.fun>
+  ```
+- Local file: quoted, relative to the current working directory or file.
+  ```fun
+  #include "./utils/file.fun"
+  ```
+- Absolute path is supported.
+
+Namespaced includes:
+- Use `as` to bind a module into a namespace alias.
+```fun
+#include <utils/math.fun> as m
+#include "examples/namespaced_mod.fun" as mod
+
+print(m.add(2, 3))
+g = mod.Greeter("Hi")
+g.say("World")
+```
+
+Aliased access uses `alias.symbol` or `alias.ClassName`.
+
+Global/private at file scope control symbol exports from a module.
+
+---
+
+## 10) Collections
+
+Arrays:
+- Literals with `[ ... ]`; may be heterogeneous unless `array<T>` is declared.
+- Helpers: `push`, `join`, `map`, `filter`, `reduce`, iteration via `for x in arr`.
+
+Maps:
+- Literal: `{ key: value, ... }`
+- Indexing: `m["a"]`, assignment `m["c"] = 5`
+- Introspection: `has(m, key)`, `keys(m)`, `values(m)`
+- Iterate keys/values using arrays returned by `keys`/`values`.
+
+---
+
+## 11) Concurrency (Threads)
+
+- `thread_spawn(fn, args)` starts `fn` in a new thread. `args` may be a single value or an array for multiple arguments.
+- `thread_join(id)` waits for the thread and returns its result.
+- `sleep(ms)` suspends current thread.
+
+Example:
+```fun
+fun square(n)
+  sleep(100)
+  return n * n
+
+ids = []
+for x in [1, 2, 3]
+  push(ids, thread_spawn(square, x))
+
+results = []
+for id in ids
+  push(results, thread_join(id))
+
+print(results)
+```
+
+---
+
+## 12) System, Files, Environment, and Networking
+
+Processes:
+- Blocking: `exec(cmd) -> string` (stdout), `system(cmd) -> number` (exit code)
+- Non-blocking: `nexec`, `nspawn`, `nsystem`, with `wait(pid)`, `read(pid)`, `kill(pid)` helpers
+
+Environment and CLI:
+- `env(NAME) -> string` to read env variables (see `os_env.fun`)
+- `argv() -> array<string>` from `<cli.fun>`; also `FUN_ARGC`/`FUN_ARGS` environment interoperability in examples
+
+Files:
+- Basic file I/O helpers exist in the stdlib; see `file_io.fun`, `file_print_for_file_line_by_line.fun`
+
+Time:
+- Date/time and timers (see `datetime_basic.fun`, `datetime_extended.fun`, `datetime_timer.fun`)
+
+Random:
+- `random` helpers (see `random_demo.fun`, `random_number_example.fun`)
+
+Regex:
+- Regex operations via stdlib (see `regex_demo.fun`, `regex_procedural.fun`)
+
+Networking:
+- TCP client helpers: `tcp_connect(host, port) -> fd`, `sock_send(fd, data)`, `sock_recv(fd, nbytes)`, `sock_close(fd)`
+- Unix domain sockets (see `unix_socket_echo.fun`)
+
+Serial:
+- Serial port helpers (see `serial_demo.fun`)
+
+Progress/UI:
+- Helper functions to render CLI progress (see `progress.fun`, `progress_inline.fun`)
+
+Note: function names may live in stdlib modules; import accordingly (system-dependent availability).
+
+---
+
+## 13) Error Handling and Type Safety
+
+- No implicit type coercion between numeric types; explicit casts or constructors are required.
+- Overflow/underflow on fixed-width types is an error.
+- Accessing undefined variables or re-defining globals is a compile-time error.
+- Shadowing internal/runtime functions is forbidden.
+- Exception syntax `try/catch/finally` is standardized in v0.3; throwing and catching at runtime may be partially implemented depending on the feature (see examples like `byte_overflow_try_catch.fun` and notes within).
+
+---
+
+## 14) Examples (from the repository)
+
+Hello:
+```fun
+print("Hello, World!")
+```
+
+Namespaced includes:
+```fun
+#include <utils/math.fun> as m
+print(m.add(2, 3))
+```
+
+Classes:
+```fun
+class Counter
+  value = 0
+  fun inc(this)
+    this.value = this.value + 1
+    return this.value
+
+c = Counter()
+print(c.inc())
+```
+
+Inheritance:
+```fun
+class Parent(number start)
+  value = 0
+  fun _construct(this, s)
+    this.value = s
+
+class Child(number start) extends Parent
+  bonus = 5
+  fun _construct(this, s)
+    this.value = this.value + this.bonus
+```
+
+Threads:
+```fun
+tid = thread_spawn(add3, [10, 20, 30])
+print(thread_join(tid))  // 60
+```
+
+TCP GET:
+```fun
+fd = tcp_connect("example.org", 80)
+req = "GET / HTTP/1.0\r\nHost: example.org\r\n\r\n"
+sent = sock_send(fd, req)
+print(sock_recv(fd, 8192))
+sock_close(fd)
+```
+
+---
+
+## 15) Versioning and Compatibility
+
+- v0.3 keeps v0.2 syntax intact and adds new features. Where runtime support is evolving (exceptions, some stdlib facets), the syntax is stable and forward-compatible.
+- Examples are authoritative for idioms and available helpers; consult `examples/` and `lib/` modules.
+
+---
+
+## 16) Appendix: Notation and Conventions
+
+- Use backticks for code identifiers in prose (`fun`, `class`, `extends`, etc.).
+- All code blocks are in `fun` pseudolanguage.
+- Indentation is always 2 spaces; tabs will cause errors.
+
+---
+
+## Changelog (from v0.2 to v0.3)
+
+- Added: `class`, methods with explicit `this`, default and custom constructors via `_construct`.
+- Added: inheritance with `extends`.
+- Added: private members by leading underscore naming convention.
+- Added: dot-call sugar `obj.method(a, b)` ≡ `method(obj, a, b)`.
+- Added: namespaced includes: `#include <path> as alias`, `#include "path" as alias`.
+- Added: `map` type with literals `{ key: value }` and helpers.
+- Added: loop control `break`, `continue`.
+- Added: threads (`thread_spawn`, `thread_join`), sleep.
+- Added: socket helpers (TCP/Unix), serial devices, CLI argv, env helpers, timers.
+- Added: bitwise helper functions: `band`, `bor`, `bxor`, `bnot`, `shl`.
+- Added: exception syntax `try/catch/finally` (runtime handling is evolving).
+
+---
+
+## How to use this file
+
+- Save this content as `./spec/v0.3.md` in the repository.
+- Keep `examples/` in sync with this spec. When adding a new feature, provide an example and update the spec accordingly.