fun/spec/v0.1.md

Fun Language Specification v0.1

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 0.1.

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. Fun and fun 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, fi, f, 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

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]

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

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!"
  fi
fi

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 "Hello, Fun!"

User-Defined Functions

Must be declared with the f prefix.

f add(a, b)
  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

9. System Integration

system

Executes a command, returns exit code.

system("ls -l")

exec

Executes a command, returns stdout.

string result = exec("date")

spawn

Executes a command asynchronously, returns process ID.

number pid = spawn("sleep 10")

10. Error Handling

• No implicit type coercion.
• Redefinition of globals is a compile-time error.
• Using undefined variables or functions is an error.
• Internal/runtime functions cannot be shadowed.

11. Examples

Hello World

print "Hello, World!"

Loop with Range

for i in range(1, 5)
  print i

User Function

f greet(name)
  return "Hello " + name

print greet("Fun")

System Call

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

12. License

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