Variables & Types

Variables are declared with let. Types are optional — you can add them for safety or leave them out for flexibility.

Variables

Use let to declare a variable. Reassign it with plain = — no let again:

let name  = "Sergio"
let count = 20
let active = true

count = count + 1   // reassignment
name  = "Ana"       // also fine

Variables declared inside a block { } are invisible outside it. You can still mutate variables from an outer scope:

let total = 0

{
    let local = 42   // only lives inside this block
    total = local    // outer variable — allowed
}

out total   // → 42
// out local  ❌ ERROR: Variable not found: local

Constants

Use const for values that should never change. Any attempt to reassign is an error:

const PI  = 3.14159
const MAX = 100

PI = 3.0   // ❌ ERROR: Cannot reassign const 'PI'

Types

Serez Code has five primitive types and several compound types:

Type annotations

Add types to function parameters and return values. When present, they're enforced at every call:

fn int add(int a, int b) {
    return a + b
}

add(1, 2)        // ✅
add(1, "hello")  // ❌ TYPE ERROR: Parameter 'b' expected 'int' but received 'string'

Skip annotations when you want flexibility — the parameter accepts any value:

fn multiply(a, b) {
    return a * b
}

multiply(3, 4)       // ✅
multiply(2.5, 4.0)   // ✅

Nullable types

Append ? to any type to allow null as a valid value:

fn int? findIndex(string target, [string] list) {
    for (let i = 0; i < list.length; i++) {
        if (list[i] == target) { return i }
    }
    return null
}

let idx = findIndex("Ana", ["Bob", "Ana", "Lee"])
if (idx != null) {
    out "Found at index {idx}"   // → Found at index 1
} else {
    out "Not found"
}

String interpolation

Embed any expression directly inside a string with {}:

let name = "Sergio"
let age  = 28
out "My name is {name} and I'm {age} years old."

let result = add(3, 7)
out "3 + 7 = {result}"

// Works with method calls too
out "Upper: {name.toUpperCase()}"   // → Upper: SERGIO

Operators

Arithmetic

out 10 + 3    // → 13
out 10 - 3    // → 7
out 10 * 3    // → 30
out 10 / 3    // → 3  (integer division, truncates)
out 10 % 3    // → 1  (remainder)
out 2 ** 10   // → 1024 (power)

// int and decimal mix freely
out 1 + 0.5   // → 1.5

Comparison & logical

out 5 > 3      // → true
out 5 == 5     // → true
out 5 != 3     // → true

out true && false   // → false (AND)
out true || false   // → true  (OR)
out !true           // → false (NOT)

Compound assignment

let n = 10
n += 5    // n = 15
n -= 3    // n = 12
n *= 2    // n = 24
n /= 4    // n = 6
n++       // n = 7
n--       // n = 6

Ternary

let x = 10
let label = x > 5 ? "big" : "small"
out label   // → big

// Chain them
let n = 2
let name = n == 1 ? "one" : n == 2 ? "two" : "other"
out name   // → two

Null coalescing

let value = null
out value ?? "default"   // → default

let maybeNum = findIndex("Ana", names)
let safe = maybeNum ?? -1   // -1 if not found

Type check

out 42 is int        // → true
out "hi" is int      // → false
out 3.14 is decimal  // → true

// Useful for functions that accept any
fn string describe(any v) {
    if (v is int)    { return "int: {v}" }
    if (v is string) { return "string: {v}" }
    return "other"
}

Comments

// Single-line comment

/* Multi-line
   comment */

let x = /* inline */ 42

Type conversions

// String → int
out parseInt("42")      // → 42
out parseInt(3.99)      // → 3  (truncates)

// String → decimal
out parseDecimal("3.14")  // → 3.14
out parseDecimal(5)       // → 5.0

// Any type → string
out 42.toString()         // → "42"
out true.toString()       // → "true"

// Read from stdin
let input = readLine("Enter a number: ")
let num = parseInt(input)