That's a good point, but it was also mentioned in the article, with a link to a useful mailing list thread[1] on the matter. It seems to be a matter of lazines

That's a good point, but it was also mentioned in the article, with a link to a useful mailing list thread[1] on the matter. It seems to be a matter of laziness. If you're writing some small piece of state like an Int, this can be a real problem. If you're writing out a lazy data structure like a list (as happens in the article), I think the extra laziness should be fine or even desired. (I've never used Writer in practice, so take my comments with a grain of salt!) [1]: http://comments.gmane.org/gmane.comp.lang.haskell.libraries/18980 http://comments.gmane.org/gmane.comp.lang.haskell.libraries/...