Foundation Source format

Lexical Structure

Klyn source files are intentionally simple to read: indentation defines blocks, comments use #, and most punctuation exists only where it improves clarity. This page covers the lexical rules you need before writing larger programs.

A Klyn Source File

#!/usr/bin/env klyn

package my.app

import klyn.math

const LIMIT = 10

def compute() as Int:
    return Int(Random.random() * LIMIT)

Not every file needs every part. The shebang is optional. Omitting the package declaration places the source in the default package; its directory never creates an implicit package. A declared package must match the source directory. Imports appear only when you need packages outside the automatically imported base package klyn.

Comments

Line comments start with #. KlynDoc-style documentation comments use the familiar /** ... */ form.

# Single-line comment
value = 10

/**
 * Documentation comment for a public API.
 */
public class Counter:
    pass

Indentation and Blocks

A block starts after a trailing :. The following lines must be indented with spaces. Misaligned blocks and tabs are syntax errors.

if total > 0:
    print("positive")
else:
    print("zero or negative")

Important

Keep top-level code flush-left. Leading indentation before a top-level statement is rejected, and tabs should not be used as indentation.

Block Scope

A variable belongs to the block in which it is first declared. It is visible from nested blocks, but never from a parent or sibling block. This rule applies consistently to if, for, while, try, catch, finally, and every branch of a match. A for binding is local to its loop.

total = 0

for value in [10, 20, 30]:
    doubled = value * 2
    total += doubled

print(total)    # 120
# print(value)  # TypeError: value is outside its scope

An assignment targets the nearest visible variable. Declare shared state before entering a control-flow block when that block must update it. A name first assigned inside the block instead belongs to that block and disappears when execution leaves it.

calculationRequired = true
result = 0

if calculationRequired:
    result = 42                 # Updates the enclosing variable.
    elapsed = 5                 # Declares a variable local to this branch.

print(result)
# print(elapsed)               # TypeError: elapsed is outside its scope.

Sibling branches never share declarations made inside one another. For a computed selection, prefer a match expression so the compiler can infer one compatible result type without leaking branch-local names.

status = 200

label = match status:
    case 200:
        "success"
    case 404:
        "not found"
    default:
        "error"

Identifiers and Naming

Kind	Typical form	Examples
Types	UpperCamelCase	`Rational`, `TimeZone`, `ArrayList`
Functions and methods	lowerCamelCase	`timeMs`, `toString`
Variables and properties	lowerCamelCase	`count`, `userName`
Private backing fields	leading underscore	`_value`, `_items`

Basic Literals

count = 10
unsignedCount = 10u
ratio = 0.5
floatRatio = 0.5f
notANumber = nan
singleInfinity = inff
utf16Unit = `A`
initial = 'A'
smile = '😀'
name = "Klyn"
message = """First line
Second line
Third line"""

Integer literals default to Int. Floating-point literals default to Double. Explicit suffixes such as u and f are useful when you want a more precise literal type at the source level. Klyn also reserves nan, nanf, inf, and inff for special floating-point values; their exact types and comparison rules are detailed in Typing and Constants.

Backticks delimit one 16-bit CodeUnit, while apostrophes delimit one Unicode scalar Char. A Char can therefore hold a supplementary character such as 😀 without splitting it into UTF-16 surrogates. See CodeUnit, Char, and Unicode for conversions and the string indexing model.

Frequently Seen Keywords

Klyn includes keywords for declarations, flow control, typing, and object-oriented features. The ones you will encounter first are:

def class if elif else match case default while for import package signal event emit return try catch finally throw const pass

Next Step

Continue with Packages and Imports before splitting code across multiple files or packages.