# Get `self` as a single identifier.
	# Return null if not a single identifier.
	fun as_id: nullable String
	do
		if self isa AMethidExpr then
			return self.collect_text
		end
		if not self isa ACallExpr then return null
		if not self.n_expr isa AImplicitSelfExpr then return null
		if not self.n_args.n_exprs.is_empty then return null
		return self.n_qid.n_id.text
	end