Referring to a previously defined variable in a GROQ query in Sanity.io

*[_type == 'devCategory'] {
 		_id,
 		"level": 0,
 		"title": coalesce(title[$lang], title.en),
        "parsedSlug": slug.current,
 		"children": *[parent._ref == ^._id] {
 		  _id,
		  "level": 1,
          "slug": ^.parsedSlug + "/", 👈👈 Here, I would get the above parsedSlug
 		  "title": coalesce(title[$lang], title.en),
 	  }
}

*[_type == 'devCategory'] {
 		_id,
 		"level": 0,
 		"title": coalesce(title[$lang], title.en),
        "parsedSlug": slug.current,
 		
} | {
   ...,
   "children": *[parent._ref == ^._id] {
 		  _id,
		  "level": 1,
          "slug": parsedSlug + "/", 👈👈 Here, I would get the above parsedSlug
 		  "title": coalesce(title[$lang], title.en),
 	  }
}