Several suggestions have been made in this thread. The one with the highest cost-to-benefit ratio would seem to be removing the Foldable constraint from Traversable, as it is simply not required by the Traversable definition. Lennart actually tried recompiling base with this "and it hardly needed any changes". I suggest that we consider this change first, as it brings the benefit of allowing Traversable types without having to define possibly nonsensical Foldable instances, and according to Lennart's experiment, has trivial impact. Lennart, what changes did you have to make? Anybody care to recompile their pet project with this change and see if there's any significant impact? -- View this message in context: http://haskell.1045720.n5.nabble.com/Proposal-Add-conspicuously-missing-Func... Sent from the Haskell - Libraries mailing list archive at Nabble.com.