Operators

This document describes all operators in Mux, including their precedence, associativity, and behavior.

Operator Precedence

Higher precedence operators are evaluated first.

Precedence	Operators	Associativity
1 (highest)	. (member access), (), []	Left-to-right
2	**	Right-to-left
3	!	Right-to-left
4	*, /, %	Left-to-right
5	+, - (binary)	Left-to-right
6	<, <=, >, >=	Left-to-right
7	==, !=	Left-to-right
8	&&, ||	Left-to-right
9	in	Left-to-right

Arithmetic Operators

Binary Arithmetic

Operator	Description	Types	Example
+	Addition	int, float, string	5 + 3, "a" + "b"
-	Subtraction	int, float	10 - 4
*	Multiplication	int, float	6 * 7
/	Division	int, float	15 / 3
%	Modulo	int, float	10 % 3 (result: 1)
**	Exponentiation	int, float	2 ** 3 (result: 8)

Arithmetic Rules

• All arithmetic operators require both operands to have the same type
• No implicit type conversion between int and float
• Division by zero is a runtime error for int, returns inf for float
• Modulo with negative numbers follows C semantics
• Arithmetic operators are builtin-only for primitive numeric types (not interface-dispatched)

Exponentiation Details

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Properties:

• Right-associative: a ** b ** c = a ** (b ** c)
• Higher precedence than *, /, %

Increment and Decrement

Operator	Description	Restrictions
++	Postfix increment	int only, standalone statement
--	Postfix decrement	int only, standalone statement

Usage Rules

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Rationale

The postfix-only, standalone-only design prevents ambiguity and side-effect confusion that can occur with prefix operators or expression-embedded increments.

Comparison Operators

Operator	Description	Types
==	Equality	int, float, bool, char, string, list, map, set, tuple, optional, result, user enums, and classes declaring Equatable, Comparable or Hashable
!=	Inequality	same as ==
<	Less than	int, float, string, and classes declaring Comparable
<=	Less than or equal	int, float, string, and classes declaring Comparable
>	Greater than	int, float, string, and classes declaring Comparable
>=	Greater than or equal	int, float, string, and classes declaring Comparable

Comparison Rules

• Both operands must have the same type
• No implicit conversion between numeric types
• String comparison is lexicographic (Unicode codepoint order)
• Collections and enums compare structurally - by their contents, not by identity. Two lists with the same elements are equal; two enum values are equal when they are the same variant carrying equal payloads. A map and a set ignore insertion order.

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What does not compare

A class does not compare with == unless it says so. Declaring is Equatable and writing eq is what opts in:

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is Comparable (which supplies cmp) and is Hashable both grant equality too, so a class needs only one of the three. See Classes for the full set.

References, function values, and the result of a void call are never comparable. Each is reported with a suggestion at the point of use.

Ordering

<, <=, > and >= accept int, float and string, plus any class declaring is Comparable. There is no ordering for collections, enums, optional or result - compare them with ==, or match on them.

Logical Operators

Operator	Description	Behavior
&&	Logical AND	Short-circuit evaluation
||	Logical OR	Short-circuit evaluation
!	Logical NOT	Unary negation

Short-Circuit Evaluation

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Implementation

The && and || operators use LLVM control flow for short-circuit evaluation:

For `a && b`:
1. Evaluate a
2. If a is false, return false (b not evaluated)
3. If a is true, evaluate b and return result

Phi nodes merge results from different branches.

Membership Operator

Operator	Description	Types
in	Membership test	T in list<T>, T in set<T>, string in string, char in string

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Collection Operators

Concatenation with +

Types	Operation	result
list<T> + list<T>	Concatenation	Combined list
map<K,V> + map<K,V>	Merge	Combined map
set<T> + set<T>	Union	Set with all elements
string + string	Concatenation	Combined string

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Compound Assignment Operators

Operator	Expansion	Types
+=	a = a + b	int, float, string
-=	a = a - b	int, float
*=	a = a * b	int, float
/=	a = a / b	int, float
%=	a = a % b	int, float

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Reference Operators

Operator	Description	Example
&	Create reference	auto r = &x
*	Dereference	*r = 42

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See Also

• Expressions - Expression evaluation rules