Chris, Thank you for the real word experience report. I had assumed (because everyone else told me) that importing qualified would be much, much better than prefixing. I had thought that in your case since you are big on model separation that you would have liked having a separate file for each model to separate out all your model related code with. As a counter point, in all of my (MVC) web application projects, we do have a separate file for each model, and we like this approach. Each file usually contains a lot of "business logic" related to the model- the only relatively empty model files are ones that really represent embedded data. When I use MongoDB (which actually supports embedded data instead of forcing you to create a separate table), I will actually place the embedded models in the same file as the model which includes them.
After my blog post complaining about records, I had a few people telling me that I can just use existing polymorphism to avoid the name-spacing issue. I collected the approaches here: http://www.yesodweb.com/wiki/record-hacks I didn't think any of those telling me what i should do had actually tried to do this themselves, particularly at any kind of larger scale. I am interested to see if anyone has experience trying this approach, or if you have considered it. On Thu, Sep 15, 2011 at 3:00 AM, Christopher Done <[email protected]>wrote: > I added my evaluation of the module-based approach to existing > records, but on second thoughts it's maybe inappropriate, so I'll post > it here. I saw that some people commented on the reddit discussion > that the solution is to put your types in separate modules but it > doesn't seem that anyone has tried to do this on a large scale. I > tried it (and some other record paradigms including Has), but I don't > think it scales. Here's why… > > Suppose I have 112 hand-crafted data types in my > project (e.g. see attachment 51369.txt[1]), this creates a lot of > conflicts in field names and constructor names. For example: > > {{{ > data Comment = Comment { > commentId :: CommentId > , commentContent :: Content > , commentReviewId :: ReviewId > , commentSubmissionId :: SubmissionId > , commentConferenceId :: ConferenceId > , commentDate :: ISODate > , commentReviewerNumber :: Int > } deriving (Show) > }}} > > This is a real type in my project. It has fields like “id”, “content”, > “reviewId”, “submissionId”, “date”. There are seven other data types > that have a field name “submissionId”. There are 15 with > “conferenceId”. There are 7 with “content”. And so on. This is just to > demonstrate that field clashes ''do'' occur ''a lot'' in a nontrivial > project. > > It also demonstrates that if you propose to put each of these 112 types > into a separate module, you are having a laugh. I tried this around > the 20 type mark and it was, apart from being very slow at compiling, > ''very'' tedious to work with. Creating and editing these modules was a > distracting and pointless chore. > > It ''also'' demonstrated, to me, that qualified imports are horrible > when used on a large scale. It happened all the time, that'd I'd > import, say, 10 different data types all qualified. Typing map > (Foo.id . BarMu.thisField) and foo Bar.Zot{x=1,y=2} becomes tedious > and distracting, especially having to add every type module when I > want to use a type. And when records use other types in other modules, > you have ''a lot'' of redundancy. With the prefixing paradigm I'd write > fooId and barMuThisField, which is about as tedious but there is at > least less . confusion and no need to make a load of modules and > import lines. Perhaps local modules would solve half of this > problem. Still have to write “Bar.mu bar” rather than “mu bar”, but > it'd be an improvement. > > I also have 21 Enum types which often conflict. I end up having to > include the name of the type in the constructor, or rewording it > awkwardly. I guess I should put these all in separate modules and > import qualified, > too. Tedious, though. At least in this case languages like C# and > Java also require that you type EnumName.EnumValue, so c‘est la vie. > > [1]: http://hackage.haskell.org/trac/ghc/attachment/wiki/Records/51369.txt > > _______________________________________________ > Glasgow-haskell-users mailing list > [email protected] > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users >
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