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:

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 available now:

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:

==
!=
<
>
<=
>=

Logical operators:

and
or
not

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 or text value.

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.

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

print(add(3, 5))

You can also define functions that do an action and return 0:

function greet(name):
    print("Hello " + name)
    return 0

greet("World")

Recursion

Recursion works and is useful for classic examples like Fibonacci.

function 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[0] is the first element
length(fruits) returns the number of elements

Built-ins

Current built-ins:

print(...)
input(prompt)
length(value)
type(value)
convert(value, "target")

Quick summary

Data types: number, text, boolean, list
Typing: dynamic at runtime, with semantic checks for names and control flow
Control flow: if, elif, else, repeat N times, while, for ... in ...
Loop control: break, continue
Functions: function name(args): and return
Blocks: indentation with spaces, not braces

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

Language Basics ​

Hello World ​

Numbers and variables ​

Text ​

Booleans ​

Input and conversion ​

Conditionals ​

Repeat loops ​

While loops ​

For loops ​

Break and continue ​

Functions ​

Recursion ​

Lists ​

Built-ins ​

Quick summary ​