On Tue, Oct 6, 2015 at 4:29 AM, Doug McIlroy
littering the code with #ifdefs
Bonus points for keeping the #ifdefs centralized
Littering is the right word. "Bonus" is merely less negative points.
It is ironic that the beautiful Haskell should progress by adopting the worst feature of C. #ifdef is a sticking-plaster for non-portable code. It is inserted at global level, usually to effect changes at the bottom of the code hierarchy. (Maybe in Haskell it should be a monad, in competition with IO for the outermost layer.)
Plan 9 showed the way out of ifdef, by putting (non-ifdef-ed) inescapably nonportable code, such as endianity, in compilation units and #include files in a distinct part of the file system tree selected by the shell.
Another trick is to use plain if rather than #if or #ifdef, and let the compiler optimize away the unwanted side of the branch.
In any event, #ifdef is, as Simon evidently agrees, telling evidence of non-portability. It is hard to imagine an uglier "solution" to keeping up with the drip-drip-drip of Haskell evolution.
The python 2→3 transition may have caused some pain to some. However it would have been far more difficult if they had not provided tools like 2to3 and six: https://docs.python.org/2/library/2to3.html http://pythonhosted.org/six/ Since the change here is trivial and pervasive why is such a tool not being considered? [Or have I missed the discussion?] In particular we can envisage a tool say 8to10 that has these modes (command-line flags) --portable --readable --info with the idea that - portable is most unreadable (ifdef litter) - readable is not portable -- generate a copy of the whole source tree that will have the changes and not be compatible for ghc < 7.8 This is for those library authors that prefer to maintain a clean code base and hell with earlier ghc versions - info summarizes which files would change and how so that a suitable reorganization of the files/directories can be done prior to the switch This is for those library authors that would like to take the trouble to have a compatibility layer and have code as readable as possible overall [Whether pure is really preferable to return is another matter -- For me one of the strongest criticisms of the python 2→3 switch is this that if they were going to break things anyhow why was the cleanup not more far-reaching? Lets keep this note in these parentheses :-) ]