Re: [Haskell-cafe] Re: Can we do better than duplicate APIs? [was: Data.CompactString 0.3]
On Mar 28, 2007, at 2:44 PM, Benjamin Franksen wrote: Robert Dockins wrote: After taking a look at the Haddock docs, I was impressed by the amount of repetition in the APIs. Not ony does Data.CompactString duplicate the whole Data.ByteString interface (~100 functions, adding some more for encoding and decoding), the whole interface is again repeated another four times, once for each supported encoding. I'd like to mention that as maintainer of Edison, I face similar difficulties. The data structure interfaces have scores of functions and there are about 20 different concrete implementations of various sorts. Even minor interface changes require a lot of tedious editing to make sure that everything stays in sync. But... you have the type of all functions nailed down in classes. Thus, even if a change in the API means a lot of tedious work adapting the concrete implementations, at least the compiler helps you to check that the implementations will conform to the interface (class); This is true. and users have to consult only the API docs, and not every single function in all 20 implementations. With ByteString and friends there is (yet) no common interface laid down anywhere. All the commonality is based on custom and good sense and the willingness and ability of the developers to make their interfaces compatible to those of others. One could use code generation or macro expansion to alleviate this, but IMO the necessity to use extra-language pre-processors points to a weakness in the language; it be much less complicated and more satisfying to use a language feature that avoids the repetition instead of generating code to facilitate it. I've considered something like this for Edison. Actually, I've considered going even further and building the Edison concrete implementations in a theorem prover to prove correctness and then extracting the Haskell source. Some sort of in-langauge or extra-language support for mechanicly producing the source files for the full API from the optimized core API would be quite welcome. Handling export lists, How so? I thought in Edision the API is a set of type classes. Doesn't that mean export lists can be empty (since instances are exported automatically)? No. Edison allows you to directly import the module and bypass the typeclass APIs if you wish. Also, some implementations have special functions that are not part of the general API, and are only available via the module exports. One could make typeclasses the only way to access the main API, but I rather suspect there would be performance implications. I get the impression that typeclass specialization is less advanced than intermodule inlining (could be wrong though). haddock comments, I thought all the documentation would be in the API classes, not in the concrete implementations. It is now, but I've gotten complaints about that (which are at least semi-justified, I feel). Also, the various implementations have different time bounds which must documented in the individual modules. Ideally, I'd like to have the function documentation string and the time bounds on each function in each concrete implementation. I've not done this because its just too painful to maintain manually. typeclass instances, etc, are quite tedious. I have to admit, I'm not sure what an in-language mechanism for doing something like this would look like. Template Haskell is an option, I suppose, but its pretty hard to work with and highly non- portable. It also wouldn't produce Haddock-consumable source files. ML-style first class modules might fit the bill, but I'm not sure anyone is seriously interested in bolting that onto Haskell. As I explained to SPJ, I am less concerned with duplicated work when implementing concrete data structures, as with the fact that there is still no (compiler checkable) common interface for e.g. string-like thingies, apart from convention to use similar names for similar features. Fair enough. I guess my point is that typeclasses (ad per Edison) are only a partial solution to this problem, even if you can stretch them sufficiently (with eg, MPTC+fundeps+whatever other extension) to make them cover all your concrete implementations. Cheers Ben Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Can we do better than duplicate APIs?
Robert Dockins wrote: Some sort of in-langauge or extra-language support for mechanicly producing the source files for the full API from the optimized core API would be quite welcome. Have you considered using DrIFT? IIRC it is more portable and easier to use than TH. Handling export lists, How so? I thought in Edision the API is a set of type classes. Doesn't that mean export lists can be empty (since instances are exported automatically)? No. Edison allows you to directly import the module and bypass the typeclass APIs if you wish. Ah, I didn't know that. Also, some implementations have special functions that are not part of the general API, and are only available via the module exports. Ok. One could make typeclasses the only way to access the main API, but I rather suspect there would be performance implications. I get the impression that typeclass specialization is less advanced than intermodule inlining (could be wrong though). No idea. Experts? haddock comments, I thought all the documentation would be in the API classes, not in the concrete implementations. It is now, but I've gotten complaints about that (which are at least semi-justified, I feel). Also, the various implementations have different time bounds which must documented in the individual modules. Yes, I forgot about that. Hmmm. Ideally, I'd like to have the function documentation string and the time bounds on each function in each concrete implementation. I've not done this because its just too painful to maintain manually. I can relate to that. The more so since establishing such time bounds with confidence is not trivial even if the code looks simple. BTW, code generation (of whatever sort) wouldn't help with that, right? I wonder: would it be worthwhile to split the package into smaller parts that could be upgraded in a somewhat less synchronous way? (so that the maintenance effort can be spread over a longer period) I have to admit, I'm not sure what an in-language mechanism for doing something like this would look like. Template Haskell is an option, I suppose, but its pretty hard to work with and highly non- portable. It also wouldn't produce Haddock-consumable source files. ML-style first class modules might fit the bill, but I'm not sure anyone is seriously interested in bolting that onto Haskell. As I explained to SPJ, I am less concerned with duplicated work when implementing concrete data structures, as with the fact that there is still no (compiler checkable) common interface for e.g. string-like thingies, apart from convention to use similar names for similar features. Fair enough. I guess my point is that typeclasses (ad per Edison) are only a partial solution to this problem, even if you can stretch them sufficiently (with eg, MPTC+fundeps+whatever other extension) to make them cover all your concrete implementations. Yes, and I think these problems would be worth some more research effort. Besides, I dearly hope that we can soon experiment with associated type synonyms... Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Can we do better than duplicate APIs?
On Wednesday 28 March 2007 17:08, Benjamin Franksen wrote: Robert Dockins wrote: Some sort of in-langauge or extra-language support for mechanicly producing the source files for the full API from the optimized core API would be quite welcome. Have you considered using DrIFT? IIRC it is more portable and easier to use than TH. DrIFT only works on datatype declarations (AFAIK) and doesn't really cover the use cases in question. [snip] haddock comments, I thought all the documentation would be in the API classes, not in the concrete implementations. It is now, but I've gotten complaints about that (which are at least semi-justified, I feel). Also, the various implementations have different time bounds which must documented in the individual modules. Yes, I forgot about that. Hmmm. Ideally, I'd like to have the function documentation string and the time bounds on each function in each concrete implementation. I've not done this because its just too painful to maintain manually. I can relate to that. The more so since establishing such time bounds with confidence is not trivial even if the code looks simple. BTW, code generation (of whatever sort) wouldn't help with that, right? Well, I can't imagine any tool that would prove the bounds for me unless automatic proof techniques have improved a _lot_ in the last week or so ;-) However, if I could record the bounds once somewhere for each implementation and then have them auto merged with the documentation for each function, that would be great. I wonder: would it be worthwhile to split the package into smaller parts that could be upgraded in a somewhat less synchronous way? (so that the maintenance effort can be spread over a longer period) Perhaps, but that only amortizes the effort rather than reducing it. [snip] As I explained to SPJ, I am less concerned with duplicated work when implementing concrete data structures, as with the fact that there is still no (compiler checkable) common interface for e.g. string-like thingies, apart from convention to use similar names for similar features. Fair enough. I guess my point is that typeclasses (ad per Edison) are only a partial solution to this problem, even if you can stretch them sufficiently (with eg, MPTC+fundeps+whatever other extension) to make them cover all your concrete implementations. Yes, and I think these problems would be worth some more research effort. Agreed. Besides, I dearly hope that we can soon experiment with associated type synonyms... Cheers Ben Rob Dockins ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Can we do better than duplicate APIs? [was: Data.CompactString 0.3]
On Wed, 2007-03-28 at 20:44 +0200, Benjamin Franksen wrote: But... you have the type of all functions nailed down in classes. Thus, even if a change in the API means a lot of tedious work adapting the concrete implementations, at least the compiler helps you to check that the implementations will conform to the interface (class); and users have to consult only the API docs, and not every single function in all 20 implementations. With ByteString and friends there is (yet) no common interface laid down anywhere. All the commonality is based on custom and good sense and the willingness and ability of the developers to make their interfaces compatible to those of others. Remember that there's more to an API than a bunch of types. The type class only ensures common types. You must still rely on the good sense and ability of the developers to ensure other properties like strictness, time complexity and simply what the functions should do. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Can we do better than duplicate APIs? [was: Data.CompactString 0.3]
Jean-Philippe Bernardy wrote: Please look at http://darcs.haskell.org/packages/collections/doc/html/Data-Collections.html for an effort to make most common operation on bulk types fit in a single framework. The last time I looked at this (shortly after you started the project) I wasn't sure if I would want to use it. Now it seems like an oasis in a desert to me. I am pretty much impressed, for instance, you managed to unify all the nine existing 'filter' types into a common type class. Cool. The only hair in the (otherwise very tasty) soup is Portability: MPTC, FD, undecidable instances which doesn't sound like it is going to replace the Prelude any time soon ;-) Never mind: I definitely consider using this instead of importing all these different Data.XYZ modules directly (and, heaven forbid, having to import them qualified whenever I need two of them in the same module). Do you forsee any particular obstacle to an integration (=providing the appropriate instances) of e.g. CompactStrings? I would even try to do this myself, as an exercise of sorts. How difficult is it in practice to work with 'undecidable instances'? Are there special traps one has to be careful to walk around? Also, we expect indexed types to solve, or at least alleviate, some problems you mention in your rant. http://haskell.org/haskellwiki/GHC/Indexed_types I have been hoping for that to resolve (some of) our troubles, but have been confused by the all the back and forth among the experts about whether they offer more, or less, or the same, as MPTCs+fundeps+whatever (and that they will probably not go into Haskell'). BTW, any reason I didn't find your collections library in the HackageDB (other than stupidity on my part)? (Just interested, I already found the darcs repo.) Cheers Ben PS: Since I read and post to the Haskell lists via gmane and a news client: Do mail clients usually respect the follow-up header, such as I insert when cross-posting, so as to restrict follow-ups to the intended list? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
