052 expand with continuations

// Test: [expand] with continuation support
//
// When an [expand] event has branches, the template produces the EXPRESSION
// that returns the union value. The continuations become switch arms automatically.
//
// This pattern:
// 1. Template produces: blk: { ... break :blk Result{ .some/none = ... }; }
// 2. Emitter detects inline_body + continuations → generates switch statement
// 3. Continuation bodies become switch arms
//
// This enables [expand] to handle branching constructs without full [transform] procs.

~import "$std/template"
~import "$std/io"

const std = @import("std");

// Template produces ONLY the expression that returns the union value
// Type is inlined since [norun] events don't generate event structs
~std.template:define(name: "maybe") {
    blk: {
        const Result = union(enum) {
            some: struct { val: i32 },
            none: void,
        };
        const __value: ?i32 = {{ expr }};
        if (__value) |v| {
            break :blk Result{ .some = .{ .val = v } };
        } else {
            break :blk Result{ .none = {} };
        }
    }
}

// Event with branches - expand detects branches and uses switch_result mode
~[norun|expand]pub event maybe { expr: Expression }
| some { val: i32 }
| none {}

// Usage - continuations become switch arms automatically
var test_value: ?i32 = 42;

~maybe(expr: test_value)
| some _ |> std.io:print.ln("Got a value!")
| none |> std.io:print.ln("Got nothing")