feat: add ternary operator support

[mjm918]

Description

Add support for ternary conditional expressions to provide concise inline conditionals.

Proposed Syntax

Standard Ternary Operator

var result: int = condition ? value_if_true : value_if_false;

Elvis Operator (truthy-based shorthand)

var result: int = maybe_value ?: default_value;

The Elvis operator ?: returns the left operand if it's truthy, otherwise returns the right operand.

Truthy values: non-zero numbers, non-empty strings, true, some(x)
Falsy values: 0, "", false, none

Note: This differs from ?? (null-coalescing) which only checks for none/null.

Examples

// Standard ternary
var max: int = a > b ? a : b;
var status: string = is_active ? "active" : "inactive";
var sign: string = x >= 0 ? "positive" : "negative";

// Elvis operator (truthy check)
var name: string = user_input ?: "Anonymous";   // "" is falsy
var count: int = cached ?: compute();            // 0 is falsy
var flag: bool = override ?: default_flag;       // false is falsy

// Difference between ?: and ??
var a: option<int> = some(0);
var x: int = a ?: 10;    // Returns 10 (0 is falsy)
var y: int = a ?? 10;    // Returns 0 (some(0) is not none)

Implementation Notes

• Ternary expressions return a value (unlike if statements)
• Both branches must have compatible types
• Elvis operator evaluates truthiness, not just null/none
• Consider precedence relative to other operators
• Short-circuit evaluation: right side only evaluated if needed

Related

This addresses the lack of inline conditionals since if is a statement, not an expression in naml.