fun/spec/v0.2.md

Fun Language Specification v0.2

Fun (Fun Uses Nothing) is a lightweight, multi-purpose programming language designed for clarity, safety, and—above all—fun.

This document defines the language syntax and semantics as of version 0.2.

1. Introduction

Fun is a scripting and systems programming language inspired by the best ideas from C, Lua, and Python—yet deliberately strict in its rules to ensure readability and consistency.

• Readable: fixed indentation rules, no ambiguous syntax.
• Strict: type safety, no implicit coercion, no silent shadowing.
• Hackable: strong system integration with safe defaults.
• Fun: simple enough to learn in a day, expressive enough for real work.

2. Lexical Structure

Case Sensitivity

Fun is case-sensitive. Hacker and hacker are different identifiers.

Identifiers

• May contain a–z, A–Z, 0–9, and _.
• Must not start with a number.

Keywords

Reserved words cannot be redefined:

if, else, for, while, fun, global, private, return, true, false.

Comments

• Single-line:

// This is a comment

• Multi-line:

/*
This is a
multi-line comment
*/

Whitespace

• Indentation is exactly two spaces.
• Tabs are forbidden.
• Line breaks terminate statements (no semicolons).

3. Data Types

Number

• 64-bit signed integer.

number n = 42

More number like (int) data types

• int8, uint8 (8bit signed and unsigned integer type)
• int16, uint16 (16bit signed and unsigned integer type)
• int32, uint32 (32bit signed and unsigned integer type)
• int64, uint64 (current number stays as int64)

Float

• 64-bit IEEE floating point.

float pi = 3.14159

String

• Double or single quotes may be used.
• ' has higher priority, so " can appear unescaped inside '...'.
• To include ' inside '...', escape with '.

string s1 = "Hello"
string s2 = 'World'
string s3 = 'He said: "Fun!"'

Boolean

• Canonical values: true, false.
• 1 and 0 are accepted in conditionals.

boolean flag = true

Byte

• Raw byte value.

byte b1 = 0x23
byte b2 = 'A'

Array

• Declared using [ ... ].

array nums = [1, 2, 3]

Supported typed arrays:

array<number> nums = [1,2,3]
array<string> names = ["Alice","Bob"]

Multidimensional arrays:

array<number> matrix = [[1,2],[3,4]]

• Arrays or dictionaries can hold different types, even if scalars are strictly typed (including objects later).

array mixed = [1, "two", true, [3,4], matrix]

4. Variables and Scope

• Global variables: accessible everywhere.
• Private variables: file-local, cannot be used outside the file.
• Redefining globals or shadowing names is forbidden.

global string message = "Hello"
private number count = 42
number nothing = 23

Dynamic variables

dynamic string x = 42
x = "Now I'm a string"

5. Operators

• Arithmetic: +, -, *, /, %
• Comparison: ==, !=, >, <, >=, <=
• Boolean: &&, ||, !
• Assignment: =

6. Control Flow

If/Else

if(x != y)
  print(x)
else if(a == b || h != i)
  print(a + b)
else
  if(k < 1 && l > 1)
    print("Buh!")

For Loops

for i in range(1, 10)
  print(i)

While Loops

while x < 10
  print(x)
  x = x + 1

7. Functions

Internal Functions

Provided by the runtime (cannot be redefined). Examples: print, range, system, exec.

print(a)
number lemmy = range(a, b)
string result = exec("date")

User-Defined Functions

Must be declared with the fun prefix.

fun add(a, b)
  return a + b

Functions support multiple return values:

fun divide(a, b)
  if b == 0
    return 0, "division by zero"
  return a / b, ""

Return Values

• Scalars: return a + b
• Arrays: return [a, b, c]

8. Modules & Includes

System Includes

Looked up in /var/lib/fun/, supporting .so (native) and .fun (Fun code).

#include crypt/md5
#include date
#include math

Local Includes

From the current working directory:

#include utils/file.fun

Absolute Includes

Full path:

#include /home/user/project/lib.fun

Aliasing

#include math as m
print(m.sqrt(16))

#include /home/user/project/universe.fun as u
print(u.size())

9. Objects

The next step... ;)

10. Reflections

Return "number", "string", etc.

string the_type_is = typeof(x)

List callable methods

array these_are_callable = methods(object)

11. Internal functions

Call Function (Dynamic Function Helper)

• f can be any callable (another function, system call wrapper, etc.).
• arg can be any type (number, string, array, object).
• This function doesn’t care about the types, it just calls f(arg).
• This function does not perform type checking on its arguments.

call(f, arg)
  return f(arg)

Example

fun add_one(x)
  return x + 1

fun shout(s)
  return s + "!!!"

print call(add_one, 41) // 42
print call(shout, "Hi") // "Hi!!!"

12. System Integration

Blocking

exec(cmd)

Executes a command, returns stdout.

string result = exec("date")

system(cmd)

Executes a command, returns exit code.

system("ls -l")

Non-Blocking

nexec(cmd)

Executes a command, returns a future-like object for async output retrieval:

object future = nexec("long_task")
result = read(future)
wait(future)

nspawn(cmd)

Executes a command asynchronously, returns process ID.

number pid = nspawn("sleep 10")

nsystem(cmd)

Executes a command, returns exit code.

number exit_code = nsystem("ls -l")

Helpers

wait(pid)

Blocks until process finishes, returns exit code.

read(pid)

Returns captured stdout (for processes started with nexec).

kill(pid)

Terminates process.

13. Error Handling

• No implicit type coercion.
• Redefinition of globals is a compile-time error.
• Internal/runtime functions cannot be shadowed.
• Compile-time: undefined variables, illegal redefinitions, type mismatch.
• Runtime: failed system calls, division by zero, etc.

14. Examples

Hello World

print("Hello, World!")

Loop with Range

for i in range(1, 5)
  print(i)

User Function

fun greet(name)
  return "Hello " + name

print(greet("Fun"))

System Call

string now = exec("date")
print("Current time: " + now)

15. License

This document and the Fun language reference are licensed under the Apache-2.0 License.