# Set that `self` is a part of comprehension array `na`
	# If `self` is a `for`, or a `if`, then `set_comprehension` is recursively applied.
	private fun set_comprehension(n: nullable AExpr)
	do
		if n == null then
			return
		else if n isa AForExpr then
			set_comprehension(n.n_block)
		else if n isa AIfExpr then
			set_comprehension(n.n_then)
			set_comprehension(n.n_else)
		else
			# is a leave
			n.comprehension = self
		end
	end