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RE: Database interface - would like advice on oracle library bind ing
by Bayley, Alistair 29 Sep '03

29 Sep '03

Yes, I know of it. Krasimir's code uses similar functions and types in the three bindings (MySQL, ODBC, PostgreSql), but the bindings do not share a common interface (AFAICT). Because they are so similar, making them support a common interface shouldn't be a lot of work. I was hoping the earlier discussions on database interfaces would converge to a solution most interested parties agreed on. I'm still sold on the left-fold interface discussed previously. Oleg claims it is sufficient, as it can be automatically converted to a stream-like interface. I bit of me agrees with you that I should be consistent with previous work, and another bit says make it simple and elegant, and this leads me towards Oleg's proposals (left-fold + auto-generated value extraction functions + auto-generated stream functions). Do others on this list (and elsewhere) have any further opinions as to how a database interface ought to look? > -----Original Message----- > From: Tim Docker [mailto:timd@macquarie.com.au] > Sent: 29 September 2003 13:43 > To: Bayley, Alistair; haskell-cafe(a)haskell.org > Subject: RE: Database interface - would like advice on oracle library > bind ing > > > > Alistair Bayley wrote: > > > Still making slow progress on an Oracle database binding... > > now I'm trying to fit the API I have into some sort of > > abstract interface (like the one(s) discussed previously: > > > Since the previous dicussion I've discovered Krasimir > Angelov's HSQL interface as part of his HTOOLKIT: > > https://sourceforge.net/project/showfiles.php?group_id=65248 > > This has a uniform abstract interface similar to the one > discussed, apparently implemented for MYSQL, ODBC, and > PostgreSQL. I've only played with the MYSQL variant. > > If possible, it would seem sensible to provide a consistent > interface for your Oracle binding. If not, it may be worth > persuading him to generalise the interface. > > Then again, perhaps you knew about this already. > > Tim ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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RE: Database interface - would like advice on oracle library bind ing
by Tim Docker 29 Sep '03

29 Sep '03

Alistair Bayley wrote: > Still making slow progress on an Oracle database binding... > now I'm trying to fit the API I have into some sort of > abstract interface (like the one(s) discussed previously: Since the previous dicussion I've discovered Krasimir Angelov's HSQL interface as part of his HTOOLKIT: https://sourceforge.net/project/showfiles.php?group_id=65248 This has a uniform abstract interface similar to the one discussed, apparently implemented for MYSQL, ODBC, and PostgreSQL. I've only played with the MYSQL variant. If possible, it would seem sensible to provide a consistent interface for your Oracle binding. If not, it may be worth persuading him to generalise the interface. Then again, perhaps you knew about this already. Tim

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RFC: "Haskell for Perl Programmers" Presentation
by Shlomi Fish 29 Sep '03

29 Sep '03

At our local Perl Mongers club we have decided to hold a series of introductions to foreign language. Being a big fan of Haskell (except for any practical use), I wrote a "Haskell for Perl Programmers" intro: http://vipe.technion.ac.il/~shlomif/lecture/Perl/Haskell/slides/ It's more or less complete, but there may still be things to add or remove. Note that until now I did not write too much about the typing facilities of Haskell. I could, though. Regards, Shlomi Fish ---------------------------------------------------------------------- Shlomi Fish shlomif(a)vipe.technion.ac.il Home Page: http://t2.technion.ac.il/~shlomif/ An apple a day will keep a doctor away. Two apples a day will keep two doctors away. Falk Fish

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RE: haddock depencies to std-modules
by Simon Marlow 29 Sep '03

29 Sep '03

> I use haddock to create documentation. Everything is fine > except of the > references to standard modules. If I am using standardtypes > like Int or > String haddock wants to create crossrefs to these modules and > fails because > of missing "sourcecode". > > Is there a simple way to fix this? I've heard of interface > files to create > right refs to existing docs, but that doesnt work. Whats the > right way? One way is to use the Haddock interface files that are distributed with GHC. I haven't put any effort into making the process easy yet - ideally Haddock should consult GHC's package database to find the interface files, but it doesn't currently do this. You'll find Haddock interface files in the same location as the documentation when you install GHC (eg. /usr/share/ghc-<version>/html/base/base.haddock on a Linux system). Cheers, Simon

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haddock depencies to std-modules
by Patrick Scheibe 29 Sep '03

29 Sep '03

hello I use haddock to create documentation. Everything is fine except of the references to standard modules. If I am using standardtypes like Int or String haddock wants to create crossrefs to these modules and fails because of missing "sourcecode". Is there a simple way to fix this? I've heard of interface files to create right refs to existing docs, but that doesnt work. Whats the right way? Cheers Patrick

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(Off-topic) Question about categories
by Peter J. Veger 27 Sep '03

27 Sep '03

> I'm not sure if anyone mentioned the examples of a poset and a monoid as categories. > There is no "internal" structure in these. In the former, the objects are the > elements and there is a morphism between a and b iff a <= b. A functor then becomes > an order preserving map. In the latter, there is one object and the morphisms are > the elements. The identity is the identity map and if x and y are two elements / > morphisms then composition is xy. A functor is then a homomorphism. > Dominic. It is probably better to use the example of a preordered set. A Preordered set is a set with a relation <=, that is reflexive (x<=x) and transtive (x<=y & y<=z --> x<=z) (but not necessarily antisymmetric, x<=y & y<=x --> x=y as for a poset). If, in a preordered set, a is the unique morphism: x -> y and b the unique morphism: y -> x, then (writing x for the identity morphism id(x)) a.b=y and b.a=x Categorically, x and y are isomorphic. Concluding that x=y is not in the categorical language. Of course, you should distinguish the category of preorders (posets, monoids) from preorder (poset, monoid) as a category. As for literature, you have the classic: Saunders Mac Lane: Categories for the Working mathematician but the working computer scientist may prefer: Andrea Asperti and Guiseppe Longo: Categories, Types, and Structures (MIT Press, 1991) Michael Barr and Charles Wells: Category Theory for Computing Science (3rd ed., Les Publication CRM, 1999) idem, Introduction to Category Theory (www.let.uu.nl/esslli/Courses/barr-wells.html) Peter J. Veger, Best, Netherlands

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(Off-topic) Question about categories
by Dominic Steinitz 27 Sep '03

27 Sep '03

Graham, I'm not sure if anyone mentioned the examples of a poset and a monoid as categories. There is no "internal" structure in these. In the former, the objects are the elements and there is a morphism between a and b iff a <= b. A functor then becomes an order preserving map. In the latter, there is one object and the morphisms are the elements. The identity is the identity map and if x and y are two elements / morphisms then composition is xy. A functor is then a homomorphism. Dominic.

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Haskell as specification language
by Luc Taesch 25 Sep '03

25 Sep '03

out of curiosity, is haskell already been used as a "specification" language ? i was thinking in a business term, rather than mathematical one. (i.e. one than " normal mortal can read, even with a bit of training ;-) I.e. one would specifiy a model, an application ( possibly run it on samples), and hand it over to developper, typically in other languages/environment... I am aware of the contracts paper of SPJ, for instance... others you may think of ? does a spec. always leads to a DSL , for instance ? I imagine a specification for an application resulting in a DSL for the "data model"/ " process model " part, (which is the generic/ reusabel part, IMH) plus something more specific to the effective application targeted... (I cannot resist explaining my long term view : if IT outsourcing really takes off one day, one key factor will be proper specification, which is in a dear state in the current practice nowadays "in the field") ref: http://search.ft.com/search/article.html?id=030923007625

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RE: Modeling multiple inheritance
by Simon Peyton-Jones 25 Sep '03

25 Sep '03

When Mark Shields and I tackled this problem we came up with Object-Oriented Style Overloading for Haskell http://research.microsoft.com/~simonpj/Papers/oo-haskell/index.htm It describes an (unimplemented) extension to Haskell, rather than modelling it in Haskell itself, but you may find it interesting none the less. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of | Brandon Michael Moore | Sent: 24 September 2003 22:22 | To: haskell-cafe(a)haskell.org | Subject: Modeling multiple inheritance | | I'm trying to build a nicer interface over the one generated by | jvm-bridge. I'm using fancy type classes to remove the need to mangle | method names. I would like methods to be automatcially inherited, | following an inheritance hierarcy defined with another set of type | classes. | | My basic classes look like this | class HasFooMethod cls args result | cls args -> result where | foo :: cls -> args -> result | | If I have classes A and B with foo methods like | foo_JA_Jint :: ClassA -> Jint -> Bool | foo_JB_Jboolean :: ClassB -> Bool -> Jint | then I can make instances | instance HasFooMethod ClassA Jint Bool | instance HasFooMethod ClassB Bool Jint | | Now I can just use foo everywhere. I would like to avoid declaring an | instance for every class though. In java methods are inherited from a | superclass, and I would like to inherit methods automatically as well. In | the bindings jvm-bridge generates a method is invoked with a function | mangled after the highest ancestor that defined that particular | overloading, so the implementation of HasFooMethod at a particular | overloading is the same for any descendant. | | So I defined a class to model the inheritance relationships | | class SubType super sub | sub -> super where | upCast :: sub -> super | | Now I can define a default instance of HasFooMethod: | instance (HasFooMethod super args result, | SubClass super sub) => | HasFooMethod sub args result where | foo sub args = foo (upCast sub) args | | This will propagate foo methods down the inheritance hierarcy. If a new | class C is derived from A, I just need to say | | instance SubClass ClassA ClassC | | and ClassC gets a foo method. (In the actually code I piggy-back on a | transitive subclass relation jvm-bridge defines that already includes an | upcast method, so upCast has a default that should always be acceptable). | | The problem comes when interfaces are added to the mix. Interfaces are | treated just like classes by jvm-bridge, and even though no implementation | is inherited from instances in Java, the method accessors generated by | jvm-bridge should be inherited. | | One problem is that the subclass relationship needs the functional | dependency so that the default instance of HasFooMethod will respects the | functional dependencies of HasFooMethod, so I can't declare subclass | instances for multiple inheritance. On the other hand, if I don't use the | functional dependency on HasFooMethod I end up needing to annotate most of | the return values in a program. I run into similar problems trying to use | numeric literals as arguments, because they are also overloaded. | | Does anyone know of clever solutions that would model multiple inheritance | while preserving the functional dependencies (unsafe compiler flags are | fine too), or ways to reduce the pain of overloading resolution without | the functional dependency? | | One alternative is generating seperate HasFooMethod instances for every | class in the system. The problem is that this would require alterating the | bit of jvm-bridge that uses JNI to find information on classes, which | currently only reports newly defined methods. JNI is black magic to me. | | Thanks | Brandon | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: Database interface - would like advice on oracle library bind ing
by Bayley, Alistair 25 Sep '03

25 Sep '03

> From: oleg(a)pobox.com [mailto:oleg@pobox.com] > > I'd like to remark first that many real databases let us avoid opening > many cursors at once. It seems to be more efficient to do as much as > possible within the engine ... I agree (and Tom Pledger makes the same comment). It's rare that I want to have more than one cursor open at once. When I've seen other developers do it, they're often doing something that would be better accomplished as a join. And that last time I remember doing it, it was a nested loops situation (which, on reflection, probably could have been done as a join... oh well). OTOH, I have seen interleaved fetches used to simulate a join where the specific DBMS product struggled to perform the join efficiently itself. In this case the developer is making up for a deficiency in the DBMS, and I don't want to exclude the option from the interface (if you agree with what you read on http://www.dbdebunk.com , then most DBMS products are deficient in a number of ways). > Still, opening several cursors may be unavoidable. The left fold > approach may still help -- we _can_ mechanically invert a left fold > combinator (to be precise, a half-baked version of it) into a lazy > list. Please see a separate message "how to invert the left fold" Found it. I'll have a look... > I believe the extract functions can be constructed automatically -- > similar to the way Quickcheck constructs test cases. I believe that > instead of I though this might be possible, but I had no idea how to do it. I'll have a look at the Quickcheck source to see how it's done, unless you can suggest a better example. > buffers. It's hard for me to write the corresponding code because I > don't have Oracle handy (besides, I like Informix better). Is it > possible to come up with a "stub" that uses flat files? We are only > interested in fetching rows. It doesn't matter if these rows come from > a file or from a database. That would make prototyping the interface > quite easier. I wasn't interested so much in prototyping the interface, as trying to write an implementation that supported the interface(s) discussed previously. I intended to provide the left-fold interface, and was wondering if that was all that was needed (for selects). Still, this would be a good exercise for me, at least so I can figure out how to generate extraction functions. > From: Tom Pledger [mailto:Tom.Pledger@peace.com] > Here's one approach: find the OCI equivalent of JDBC's > ResultSetMetaData, and use it to drive the allocation and freeing of > buffers. I've considered this, and I think it's the next route I'll take (the OCI supports it). At the least it'll give me the ability to perform arbitrary queries (at present I have to know the types of the result set columns and construct the extraction function manually). I've also considered stuffing more information into the Cursor type (which I've introduced), and using this in a modal fashion to decide what to do at each point. > Here's another: ... > Make getInt (and friends) behave differently depending on the mode > of the cursor they're passed: either allocate a buffer and return > _|_, decode and return the current column of the current row, or > free a buffer and return _|_. Not wanting to sound too dumb, but how do you return _|_ ? Thanks, Alistair. ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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