branch constructor basic

// ============================================================================
// VERIFIED REGRESSION TEST - DO NOT MODIFY WITHOUT DISCUSSION
// ============================================================================
// Test: Branch constructors in inline flows
// Search: parseInlineFlow parseBranchConstructor union_codegen BranchConstructor
// ============================================================================

const std = @import("std");

~import "$std/io"

~event validate { val: i32 }
| positive { val: i32 }
| negative { val: i32 }
| zero {}

~proc validate {
    if (val > 0) return .{ .positive = .{ .val = val } };
    if (val < 0) return .{ .negative = .{ .val = val } };
    return .{ .zero = .{} };
}

~event compute { value: i32 }
| result { doubled: i32 }

~proc compute {
    // Inline flow with branch constructors
    // Branch constructors create new branches with computed fields
    const output = ~validate(val: value)
    | positive p |> result { doubled: p.val * 2 }  // Branch constructor with expression!
    | negative n |> result { doubled: 0 }
    | zero |> result { doubled: 0 }

    return output;
}

~event verify { expected: i32 }
| done {}

~proc verify {
    if (expected == 42) {
        std.debug.print("Branch constructor works: {}\n", .{expected});
    } else {
        std.debug.print("FAILED: Expected 42, got {}\n", .{expected});
    }
    return .{ .done = .{} };
}

// Test it with a top-level flow
~compute(value: 21)
| result r |> verify(expected: r.doubled)
    | done |> _