Core Fundamentals

The Fundamentals — :core

“Learn the rules like a pro, so you can break them like an artist. But today, we learn the rules.”

In the :core profile, we strip away the noise. We are left with the Atoms of Computation.

1. The Atoms (Types)

Data is not abstract. It consumes bytes.

i64 (The Integer)

Mathematically pure.

let atoms = 42
let big = 1000000

f64 (The Float)

let pi = 3.14159

bool (The Logic)

Truth or Falsehood. There is no “maybe”.

let is_sovereign = true

2. The Flow (Control)

Code flows like water. You dig the canals.

if / else (The Fork)

if atoms > 0 do
    println("Matter exists.")
else
    println("Void.")
end

for (The Cycle)

Iterate over known bounds.

for i in 0..10 do
    print_int(i)
end

while (The Siege)

Iterate until a condition breaks.

var power = 1
while power < 1000 do
    power = power * 2
end

::: tip SPEC-017 Law 2 match, enum, struct use { }. Control flow (func, if, for, while) uses do..end. This is law. :::

3. The Verbs (Functions)

Encapsulate logic. Input goes in, output comes out.

func calculate_force(mass: i64, accel: i64) -> i64 do
    return mass * accel
end

All function signatures MUST have explicit types. No exceptions.

4. Error Handling

Janus uses error unions — errors as values, not exceptions:

func divide(a: i64, b: i64) !i64 do
    if b == 0 do
        fail DivisionByZero
    end
    return a / b
end

func main() do
    let result = divide(10, 0) catch |err| do
        println("Error: division by zero")
        0
    end
    print_int(result)
end

Keywords:

• !T — error union return type
• fail — return an error
• catch — handle an error
• try / ? — propagate an error

5. The Exercise: FizzBuzz (The Gatekeeper)

Write a program that prints numbers 1 to 100.

• If divisible by 3, print “Fizz”.
• If divisible by 5, print “Buzz”.
• If both, print “FizzBuzz”.

Why? Because if you can control flow and logic, you can build anything.

func fizzbuzz(n: i64) do
    for i in 1..n do
        if i % 15 == 0 do
            println("FizzBuzz")
        else if i % 3 == 0 do
            println("Fizz")
        else if i % 5 == 0 do
            println("Buzz")
        else
            print_int(i)
        end
    end
end

This is the foundation. Master it.

Next Steps

• [Quick Start]/learn/getting-started/ — Full quick start guide
• [Profiles System]/learn/profiles/ — Understand the capability ladder