cue export ./hello
cmp stdout expect-stdout
-- expect-stdout --
{
    "$type": "demo",
    "message": "Hello World!"
}
-- hello/data.cue --
package hello

#who: "World"
-- hello/hello.cue --
package hello

$type:   "demo"
message: "Hello \(#who)!" // who declared in data.cue
-- hello/cue.mod --