Expressions

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---
title: Expressions
description: The building blocks of logic, from literals to complex postfix chains.
icon: Binary
---
Expressions in Mist are the fundamental units that evaluate to a value. The syntax follows a clean **prefix → primary → postfix** chain, providing a predictable structure that maps closely to Rust's mental model.
## Primary Expressions
Primary expressions are the starting point of any logic chain. These include literal values, paths to static members, or grouped expressions in tuples.
```java
// Literals and paths
var x = 42;
var y = Math::PI;
// Tuples
var coordinates = (10, 20, 30);
```
## Postfix Operations
Postfix expressions allow you to build on a primary value. This includes calling functions, accessing fields, indexing arrays, or initializing structs.
```java
// Field access and method/function calls
var len = list.length();
// Struct initialization
var task = Task {
name: "Drafting",
priority: 1,
};
// Indexing and Macro calls
var first = items[0];
println!("Value: {}", first); // Macro call via '!'
```
## Prefix Operations
Prefixes modify the primary expression that follows them. Mist uses these for logical negation, dereferencing, and creating references.
```java
var mut value = 10;
var ref = &value; // Reference
var mref = &mut value; // Mutable reference
var val = *ref; // Dereference
var is_false = !true; // Logical NOT
```
## Binary Operations
Binary operations are applied as postfixes to an expression, following a `bin_op ~ expr` pattern. This supports all standard arithmetic, comparison, and logical operators.
```java
var sum = 10 + 20;
var is_equal = (x == y);
var complex = (a + b) * (c / d);
```
## Operator Table
Mist supports the following binary operators for comparisons and arithmetic:
| Category | Operators |
| -------------- | -------------------------------- |
| **Arithmetic** | `+`, `-`, `*`, `/`, `%` |
| **Comparison** | `==`, `!=`, `<`, `>`, `<=`, `>=` |
| **Logical** | `&&`, `\|\|` |
## Key Characteristics
- **Predictable Chaining**: The `prefix* ~ primary ~ postfix*` grammar ensures that complex expressions are parsed consistently, whether you are dereferencing a function call or indexing a struct field.
- **Rust-Style References**: While the pointer syntax `type*` is used in declarations, expressions use `&` and `&mut` to create references, maintaining compatibility with Rust's borrow checker.
- **Macro Integration**: Macros are treated as a postfix operation (`!`), allowing them to be called on identifiers just like standard functions.
- **Unified Tuples**: Tuples are primary expressions, allowing them to be passed, returned, or destructured seamlessly within the expression tree.
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"---[ArrowDownUp]Logic---",
"logic/variables",
"logic/control-flow",
"logic/match-patterns"
"logic/expressions"
]
}