flatten.oz

% if head is nil then answer
% if head is integer then append it to answer and flatten tail
% if head is list then flatten head and then flatten tail

declare
fun {FlattenList L}
   local FlatLoop in
	  fun {FlatLoop L1 Acc}
		 case L1
		 of nil then Acc
		 [] (H|T1)|T then
			{FlatLoop T {Append Acc {FlatLoop H|T1 nil}}}
		 [] H|T then {FlatLoop T {Append Acc [H]}}
		 end
	  end
	  {FlatLoop L nil}
   end
end

{Browse {FlattenList [1 2 3]}}
{Browse {FlattenList [[1] [2]]}}
{Browse {FlattenList [1 2 [3] 4]}}