Types and Values

XE is dynamically typed. Values carry their type at runtime, and operations either succeed according to XE's rules or fail with a runtime error.

The four runtime types

XE currently has four value kinds:

Type	Example	Notes
number	42, 3.14	Stored as numeric runtime values
text	"hello"	Double-quoted strings
boolean	true, false	Used directly in conditions
list	[1, 2, 3]	Ordered collections with zero-based indexing

Check a value's runtime type with type(...):

print(type(42))
print(type("XE"))
print(type([1, 2, 3]))

Variables are mutable

XE currently has variables, not constants.

score = 10
score = score + 5
print(score)

There is no separate const keyword right now. Reassignment is allowed unless the name is out of scope.

Numbers

Numbers support:

• +
• -
• *
• /
• %

price = 99.5
tax = 0.5
print(price + tax)

Division and modulo by zero raise runtime errors instead of silently returning fallback values.

Text

Text values use double quotes.

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

+ also performs concatenation if either operand is text.

print("Count: " + 3)

That produces text output.

Booleans and truthiness

Boolean literals are:

• true
• false

Conditions also use truthiness rules:

• 0 is falsey
• non-zero numbers are truthy
• "" is falsey
• non-empty text is truthy
• [] is falsey
• non-empty lists are truthy

Example:

if [1, 2]:
    print("non-empty lists are truthy")

Lists

Lists are array-like collections backed by Rust Vec, so indexing is natural and efficient.

items = [10, 20, 30]
print(items[0])
print(length(items))

Important current rules:

• indexing is zero-based
• negative indexing is not supported
• out-of-bounds access is a runtime error
• list mutation is not implemented yet

Conversion rules

convert(value, target) supports three targets:

• "number"
• "text"
• "boolean"

Examples:

print(convert("42", "number"))
print(convert(123, "text"))
print(convert("", "boolean"))

Current behavior:

• text to number must parse successfully
• invalid text-to-number conversion fails at runtime
• booleans convert to 1 or 0 when targeting "number"
• lists cannot be converted to numbers

Equality and comparison

Comparison operators:

• ==
• !=
• <
• >
• <=
• >=

Ordering comparisons (<, >, <=, >=) are numeric comparisons. If you use them on non-number values, XE raises a runtime error.

Equality compares values of the same runtime kind naturally. Different runtime kinds are not treated as equal.

print(5 == 5)
print("xe" == "xe")
print(true == 1)

The last line evaluates to false, not to an implicit coercion.

Next steps

• Continue with Control Flow
• Or jump to Functions and Scope