Language Basics

XE is intentionally small. The syntax is indentation-based and close to Python in shape, but the compiler lowers everything into Rust.

If you want the book-like path through the docs, read the chapters in this order:

1. Syntax and Blocks
2. Types and Values
3. Control Flow
4. Functions and Scope
5. Runtime Behavior and Errors

Hello World

Every language starts with printing a message.

print("Hello, World!")

print is a built-in function. It writes values to the screen.

Numbers and variables

Variables are just names that hold values.

x = 10
y = 20
print(x + y)

What happens:

• x gets 10
• y gets 20
• x + y evaluates to 30
• print shows the result

Arithmetic operators:

• +, -, *, /
• // divides and rounds down, % is the remainder, ** is power
• x += 1 is short for x = x + 1 (also -=, *=, /=, //=, %=, **=)

Text

Text values are written in double quotes.

name = "XE"
print("Hello " + name)

The + operator can also join text values.

Booleans

Boolean values are true and false.

ready = true
print(type(ready))

Input and conversion

input() always returns text, even when the user types digits. Convert it before using it as a number.

age_text = input("Enter your age: ")
age = convert(age_text, "number")

if age >= 18:
    print("Adult")
else:
    print("Minor")

Valid conversion targets currently documented in XE:

• "number"
• "text"
• "boolean"

Conditionals

XE uses indentation-based blocks for if, elif, and else.

score = 82

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
else:
    print("Keep going")

Comparison operators: ==, !=, <, >, <=, >= (numbers, or text alphabetically), and in / not in for membership.

Logical operators: and, or, not. As in Python, not x == 5 means not (x == 5).

Conditions can be any value: 0, "", [], {}, none and false count as false.

Variables assigned inside an if block are still available after it.

Repeat loops

XE currently has fixed-count loops through repeat N times.

repeat 3 times:
    print("XE")

N can be a number or a variable that stores a number.

Assignments inside the loop update outer variables if they already exist:

count = 0

repeat 3 times:
    count = count + 1

print(count)

While loops

Use while when the loop should keep running until a condition becomes false.

count = 0

while count < 3:
    print(count)
    count = count + 1

For loops

Use for name in iterable to walk through a list, a text value, the keys of a map, or a range of numbers.

for i in range(3):
    print(i) # 0, 1, 2

total = 0

for item in [1, 2, 3]:
    total = total + item

print(total)

For text, XE iterates one character at a time:

for ch in "XE":
    print(ch)

Break and continue

Inside repeat, while, and for loops you can use:

• break to leave the loop immediately
• continue to skip to the next iteration

count = 0

while true:
    count = count + 1
    if count == 2:
        continue
    if count == 4:
        break
    print(count)

Functions

Functions let you name reusable logic.

fun add(a, b):
    return a + b

print(add(3, 5))

A function that does not return a value gives back none:

fun greet(name):
    print("Hello " + name)

greet("World")

Functions are values too: pass them to other functions, or write small ones inline with lambda x: x * 2.

Modules

XE can import from other .xe files.

from math_utils import double
print(double(21))

Or import the whole module and use its name:

import helpers
print(helpers.square(4))

Imports resolve relative to the current file and must come before executable top-level statements.

Recursion

Recursion works and is useful for classic examples like Fibonacci.

fun fib(n):
    if n <= 1:
        return n
    return fib(n - 1) + fib(n - 2)

print(fib(10))

Lists

Lists hold ordered values.

fruits = ["apple", "banana", "cherry"]
print(fruits[0])
print(length(fruits))

Notes:

• list indexing starts at 0; fruits[-1] is the last element
• fruits[1:] is a slice: a new list without the first element
• fruits.append("date") adds to the end (same as append(fruits, "date"))
• length(fruits) returns the number of elements

Built-ins

XE has built-in functions for text (upper, split, replace, ...), lists (append, pop, sort, ...), maps (keys, values, ...), math (abs, round, sqrt, min, max, ...), files (read_file, write_file, ...) and the program (args, exit, error). See the Language Reference for the full list.

Quick summary

• Data types: number, text, boolean, none, list, map, struct, function
• Typing: inferred; known numbers, text and booleans compile to native values
• Control flow: if, elif, else, repeat N times, while, for ... in ..., try / catch
• Loop control: break, continue, pass
• Functions: fun name(args):, return, and lambda
• Blocks: indentation with spaces, not braces

For the more detailed version of each topic, continue with:

• Syntax and Blocks
• Types and Values
• Control Flow
• Functions and Scope
• Runtime Behavior and Errors