Documentation

Introduction

This is the initial design document for the Cu language. At this stage, it summarizes the philosophy and proposed syntax, and is not a formal language specification. Before starting implementation, ambiguities in syntax, type rules, error handling, and execution model need to be finalized.

Design Philosophy

Three principles serve as the criteria for design decisions.

• Accessibility: Aiming for a language that is easy to learn and supports a wide range of developers and applications.
• Performance: Pursuing execution speed and memory usage from the language specification and runtime design stage.
• Control: Aiming to enable necessary control considering the characteristics of the execution environment and hardware.

Basic Syntax (Draft)

The following are under consideration. Not all are finalized or implemented.

File Format

main.cu29

Directives

#mode 
#apply 

Standard Output

Io.print(none: str = "Hello, World!")

Variable Declaration and Initialization

x: int = 1
name: str = "Cu"
pi: float = 3.14
enabled: bool = True

Candidate basic types: int (integer), float (floating-point), str (string), bool (boolean)

Reassignment

x: int = 1

x = 3
x += 1

Direct Value Specification with none

Io.print(none: str = "Cu")

Under consideration. Not confirmed to have the same meaning as None/null in other languages.

Function Definition

fnc: int = init() {
    Io.print(none: str = "a")
    return none: int = 0
}

Multiple Return Values

fnc: (int, str) = get_values() {
    return none: int = 10, none: str = "Cu"
}

a, b = get_values()

Conditional Branching

if: pro = x == 0 {
    Io.print(none: str = "x is 0!")
} elif: pro = x == 1 {
    Io.print(none: str = "x is 1!")
} else {
    Io.print(none: str = "x isn't 0 or 1!")
}

Loop: for

for: pro = 5 {
    Io.print(none: str = "Hello")
}

Loop: while

while: pro = x == 0 {
    Io.print(none: str = "x is 0")
}

while: pro = True {
    Io.print(none: str = "Running")
}

Loop Control

break
continue

Operators and Multi-line Expressions

result: int = 10 + 20
value: int = result * 2

result: int = 10 +
    20

Specification Status

Item	Status
Language name Cu	Confirmed
Extension .cu29	Confirmed
Initial implementation in Python	Policy
No classes in initial spec	Policy
APC three principles	Content confirmed
Syntax for variables, functions, conditionals	Draft
Meaning of none	Needs definition
Precise meaning of pro	Needs definition
Type system	Needs design
Memory management	Needs design
Compilation / execution model	Needs design
RTOS / hardware control features	Future consideration

Important: This is currently an initial design document summarizing the philosophy and syntax proposals of Cu, not a formal language specification.