085 effect branch resume arithmetic

// Test: effect-branch handler resumes with an arithmetic expression
// using the binding. `n * 2` should evaluate the Zig expression and
// send the result back as the resume value.

~import "$std/io"

~pub event request { payload: i32 }
! double i32 -> i32
| done i32

~proc request|zig {
    const result = double(payload);
    return .{ .done = result };
}

~request(payload: 21)
! double n |> n * 2
| done r |> std.io:print.blk {
    result is {{ r:d }}
}