## 11. Advanced Topics

### 11.1 Dynamic Code Evaluation

The `eval` operator executes code dynamically at runtime by parsing and executing a TokenString.

**Syntax**: `{ code } eval`

**Examples**:
```
// Evaluate simple expression
"2 3 +" eval            // Pushes 5

// Build and execute code
"(Multiplyable -- Multiplyable) { dup * } ::square fn" eval
5 square                // 25

// Dynamic dispatch
operation_name " get" concat eval
```

**Use Cases**:
- Building code at runtime
- Dynamic dispatch based on runtime values
- Implementing interpreters or REPLs
- Meta-programming

**Warnings**:
- Eval introduces runtime overhead (parsing)
- Type safety is reduced (types checked at eval time, not compile time)
- Security risk if evaluating untrusted code
- Use sparingly and prefer static alternatives when possible

### 11.2 Identifier Literals

Identifier literals use the `::` prefix to push an identifier as a value rather than executing it.

**Syntax**: `::name`

**Context-Dependent Rules**:

**In function bodies and eval**: `::` is required for identifier literals
```
::Point                 // Pushes identifier "Point"
::Addable              // Pushes identifier "Addable"
```

**In trait definitions**: `::` is not allowed (identifiers are method names)
```
{
    (Self -- ) draw:    // "draw:" is a method name, not a literal
} ::Drawable trait
```

**In trait implementations**: `::` is not allowed (identifiers are method names)
```
::Drawable {
    (Self -- ) { ... } draw:  // "draw:" is a method name
} ::Rectangle impl
```

**Use Cases**:
- Defining structs: `(T T --) { x: y: } ::Point<T> struct`
- Defining traits: `{ ... } ::Drawable trait`
- Field access: `point ::x get`
- Dynamic trait operations
- Meta-programming

### 11.3 Standard Library

The standard library provides I/O, string operations, type conversions, and utility functions. All standard library functions are automatically in scope (no imports needed in current version).

**I/O Operations**:
```
"Hello" print           // Print string to stdout
"Enter name: " input    // Read line from stdin
"file.txt" read         // Read file contents as string
"data" "file.txt" write // Write string to file
```

**String Operations**:
```
"hello" " world" concat     // Concatenate strings
"hello" length              // Get string length
"hello" 1 3 substr          // Extract substring
"a,b,c" "," split           // Split by delimiter
["a" "b"] "," join          // Join with delimiter
```

**Type Conversion**:
```
42 to_f64               // Convert i32 to f64
3.14 to_i32             // Convert f64 to i32 (truncates)
"123" parse             // Parse string to inferred type
42 to_str               // Convert to string
```

**Array Operations**:
- Element access: `at`, `slice`
- Information: `length`, `shape`
- Combinators: `map`, `filter`, `reduce`, `each`
- Manipulation: `concat`, `reverse`, `transpose`, `window`

> **Complete Reference**: See Appendix A for the full standard library reference with all functions, signatures, and examples.

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