Hi everyone, I noticed that xmonad and xmonad-contrib both prefer to use of String = [Char] for their stringy data-types. This is probably a terrible idea. I cite some sources here, then outline their arguments below. http://www.alexeyshmalko.com/2015/haskell-string-types/ https://mail.haskell.org/pipermail/haskell-cafe/2014-June/114745.html __String is Bad__ 1) Char is a horribly inefficient representation of a character, being an entire machine word in length (at least 32 bits). Actually, it's worse: each Char takes up _two_ machine words in GHC, since it needs one to store GC information in. See the slide in the first link for more details. Data.Text stores the characters in compact arrays. 2) Lists are lazy, which makes their evaluation slower. You have to thunk on each character, which is pretty silly most of the time. Normally you want to read in at least _chunks_ of string all at once. Data.Text is strict, but Data.Text.Lazy exists and is (as you would assume) lazy when you need it. The long and the short of it is that [Char] is a suboptimal choice to use for anything except possibly short identifiers; Haskell (via GHC) is a compiled language, and yet performs orders of magnitudes worse than even Perl and Python on text processing when using Data.String. There is simply no good reason to use String when Text exists. __Alternatives__ The other alternative is ByteString. Although ByteString is a great type for binary data, and specifically for data exchange protocols, it seems that it would inappropriate in this situation, due to the replacement of most (if not all) instances being actual textual data, which obviously Text is optimized for. __Migration Issues__ Assuming we can agree that Text > String then, the main problem to switching would be the pain of migration, and whether this would be worth it. I argue it wouldn't be so bad, and is worth doing on principle alone. The LANGUAGE pragma of OverloadedStrings allows you to use String literals as Text literals, so that wouldn't be the main problem. The main issue is changing all the interfaces so they accept Text instead of String, and how this would impact existing user configs, and the xmonad-contrib archive. Every time you use ++ you would have to replace it with <>, the Monoid infix mappend operator. I doubt many people use : to build Strings, but in those instances those would have to be changed too. Finally, pattern matching on Strings like (x:xs) would break as well. All other functions would require changing from their String/List counterpart to the Text one. Since the names clash, one would have to import qualified as, for instance, T and call T.intersperse or whatever. It would be a non-trivial undertaking, but certainly doable. __Other Breaking Changes__ Are there other niggling issues that exist in the codebase that would cause breaking changes? Perhaps it would be a good idea to get a list of them all and see if it's worth breaking backwards compatibility to fix them all at once? I'm a purist when it comes to code, but I would like to hear what other people think, and just how angry they would be with this change. I have no idea as to what xmonad and xmonad-contrib's breaking changes policy is. Obviously I'm not proposing this change be undertaken for 0.13 -- I was aiming for more 0.14 or later. Let me know what you think. Sincerely, Matt