Re: [Haskell] What are possible causes of "C stack overflow" in Hugs?

The simplest and safest solution is to change foldl to foldl', but it produces the unnecessary evaluation of `elem`s in addSetElem's.

Wrong. Please ignore it. $!! is better in a sense that it reduces the stack usage further than foldl' (foldl''s second argument needs stacks to be evaluated). -- Koji Nakahara