Hi Sven,
the library documentation says: "Portability: portable", but this is not the case at all, wxHaskell uses quite a few extensions (apart from the FFI, which can be considered portable nowadays):
wxHaskell consists of two layers: WXCore and WX. The WXCore layer is supposed to be totally Haskell98 compatible (or really easy to make compatible). The WX layer is a nice haskellized version of the wxWindows API on top of WXCore that uses extensions.
* wxcore/src/Graphics/UI/WXCore/IntMap.hs fiddles around with unboxed values and GHC interna for performance reasons. Is this really necessary? (Apart from that, it triggers a bug in GHC's new Lexer :-}
No, it is not. Actually on http://www.cs.uu.nl/~daan/ddata.html you can find a Hugs98 and "standard" haskell98 version. I just used this one as I only use GHC but it can easily be replaced.
* The default declaration of setBitMask in wx/src/Graphics/UI/WX/Types.hs uses a scoped type variable. This could probably be rewritten to something more portable.
Thanks for the hint. I'll remove the type declaration.
* wx/src/Graphics/UI/WX/Attributes.hs uses existentially quantified data constructors (:=, :~, ::=, and ::~) for purely aesthetical reasons.
* Type synonyms in instance heads + complex instance heads are quite
Yes, I am considering changing it to "=:" operators, that look less nice, but remove the dependency on rank-2 polymorphism. However, I haven't removed them yet as 1) not enough people complained, 2) any serious haskell compiler supports "forall" now, and 3) the (:=) operator looks *really* good, and 4) I depend on more devious things already which are harder to avoid, namely: pervasive: This is a devious thing to do, but totally unavoidable given the way I model inheritance with phantom types. I have considered using type classes to model the inheritance but that leads to a) other dependencies on extensions, b) hard to understand error messages, and c) a much more complex model. (See Andre Pang's master thesis for a ingenious way to model full inheritance) On the other hand, phantom type inheritance is easy *and* using type synonyms in instance heads is *very* convenient (a huge improvement compared to all the instance declarations I had to write for GIO). (So, I guess I am making a case for supporting this extension in future Haskells as it is so useful).
* wx/src/Graphics/UI/WX/Classes.hs uses MPTC with functional dependencies.
Hmm, yes, but these could be removed -- they are not very important.
I don't want to sound too negative, Daan has done an impressive job, but I'm a bit concerned about all this non-portable stuff when we are planning to use wxHaskell as the basis for our GUI efforts.
I share your concerns. However, keep in mind that WXCore is Haskell98 + FFI, and that only the nicified abstraction WX uses extensions. That is, anyone can build another nicified abstraction that is H98 compatible. However, it seems that for "real" libraries, one wants a bit more power. In the end though, I would like wxHaskell to be an open community effort and not to be "daan's" library. In that sense, anyone can change the libraries interface if enough people support that. I am not emotionally attached to my design and will certainly support people that want to change or fix the library (especially given my lack of time to spend on this project :-). All the best, and thanks for your comments, Daan.
Cheers, S.
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