Hello, I am using "import Debug.Trace" to debug some code but it is not working as expected. I believe this is due to lazy evaluation. But I cannot see how I can circumvent it. To exemplify I have the following function: tagFun :: (POSTags -> Tag) -> POSTags -> POSTags tagFun f corpus = Z.foldlz' tag Z.empty corpus where tag acc z = Z.insert newTag acc where (token, correctTag, _proposdTag) = trace "cursor " Z.cursor z proposed = trace "proposed tag" (f z) newTag = ( token, correctTag, proposed ) If I place tracing at: tag acc z = trace ("tag "++token++" = "++ show newTag) Z.insert newTag acc then it works ok. However the lines (token, correctTag, _proposdTag) = trace "cursor " Z.cursor z proposed = trace "proposed tag" (f z) don't work. They only appear once. I assume they should appear with every element in the zipper. Can anyone explain why? TIA, Hugo F.