Decisions with if / else

An interesting program must be able to make decisions: "if it rains, bring an umbrella". In AHA! Lang, decisions are written with if and else.

Basic Form

let nilai = 80;

if nilai >= 70 {
    print_str("Lulus\n");
} else {
    print_str("Tidak lulus\n");
}

Structure:

if <condition> {
    ...code if the condition is true...
} else {
    ...code if the condition is false...
}

• The condition is an expression that produces 1 (true) or 0 (false) — usually a comparison.
• The else block can be omitted if it's not needed.

if / else Is an Expression

Here's AHA! Lang's quirk: if/else produces a value. That value is the result of the last expression in the branch that runs.

let x = 10;
let y = 20;

let terbesar = if x > y { x } else { y };

print(terbesar); // 20

No variable is filled inside a branch — the branch produces its value directly. This makes the program shorter and clearer.

Compare it to the usual imperative style (which also works):

let terbesar = 0;
if x > y {
    terbesar = x;
} else {
    terbesar = y;
}

Both ways are valid, but the expression version avoids the initial terbesar value that could be misunderstood.

Nested Branches

An else branch can contain another if — for tiered decisions:

let nilai = 85;

// grade: A if >= 85, B if >= 70, otherwise C
let grade = if nilai >= 85 {
    "A"
} else {
    if nilai >= 70 {
        "B"
    } else {
        "C"
    }
};

print_str(grade + "\n"); // A

Note: each branch returns a string, so the variable grade has type String.

Combining Conditions

Combine multiple conditions with && and ||:

let umur = 20;
let punya_ktp = 1;

if umur >= 17 && punya_ktp == 1 {
    print_str("Boleh membuat KTP\n");
}

AHA!'s Compositional Value System

Because if is an expression and logic results are Int, everything can be chained freely:

let x = 42;

// "Fizz" inspiration from FizzBuzz: multiples of 3
let label = if x % 3 == 0 { "Fizz" } else { "Bukan Fizz" };

print_str(label + "\n");

This is one of the things that makes AHA! Lang feel like a "composable alphabet".

Exercises

1. Write a program that prints "Genap" or "Ganjil" based on a number variable (hint: angka % 2).
2. Create a function tanda(n) that returns "Positif" if n > 0, "Negatif" if n < 0, and "Nol" if n == 0. (Hint: nested branches.)
3. Use if as an expression: store in a variable diskon — 10 if total > 100000, otherwise 0 — then print total - diskon.

On to Looping with while