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Opportunity for Haskell porting to java at R&D labs in Bay Area, CA
by Padma 12 Nov '10

12 Nov '10

We are looking for a entry level Haskell programmer who has experience in porting from Haskell to java. Please contact me by Email or you can call me at 408-207-9367. LOCATION: SUNNYVALE, CA DURATION: 6 MONTHS Degree: Bs or Ms or Ph.D Start immediately Good experience in porting particularly from Haskell to java environment. Check and validate smooth functioning of the system.(After porting is done) This is a R&D project. (prior experience is desired) Good experience in testing and compiling. Regards, Padma SRAOSS INC. 5300 Stevens Creek Blvd Suite 460 San Jose,CA 95129 Direct:(408) 207-9367 Tel: (408) 855-8200 x 321 Fax: (408) 855-8206 <blocked::mailto:padma@sraoss.com> padma(a)sraoss.com <blocked::http://www.sraoss.com/> www.sraoss.com <blocked::http://www.sra.co.jp/> www.sra.co.jp

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Re: Haskell-cafe] Serialization of (a -> b) and IO a
by John Lato 12 Nov '10

12 Nov '10

> > Message: 3 > Date: Thu, 11 Nov 2010 18:56:00 +0100 > From: Sjoerd Visscher <sjoerd(a)w3future.com> > > On Nov 11, 2010, at 6:34 PM, John Lato wrote: > > > I don't know to what extent it would apply in this hypothetical > situation, but ghc (and probably other compilers) rely upon Haskell's > semantics in performing various code transformations. If you break the > semantics some transformations become invalid, resulting in incorrect code. > > > > I've experienced this with code that violated ref. transparency. The > program behavior changed depending on the compiler's optimization settings. > I'm not keen to go back to that. > > Then don't do that. Being able to serialize functions is just as dangerous > as having unsafePerformIO. If you don't use it, you don't have problems. > If you do use "serialize", I think it would cause problems most of the time. A pure serialization would violate referential transparency. GHC relies upon referential transparency for some transformations to be valid. Therefore it's not possible to use a pure serialization function safely unless the user can guarantee that it's only used in a referentially transparent manner, which is an extremely high barrier IMO (higher than for unsafePerformIO). John

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Re: [Haskell-cafe] Serialization of (a -> b) and IO a
by John Lato 12 Nov '10

12 Nov '10

> > From: Sjoerd Visscher <sjoerd(a)w3future.com> > > On Nov 11, 2010, at 3:36 PM, Dan Doel wrote: > > > On Thursday 11 November 2010 6:22:06 am Sjoerd Visscher wrote: > > > >> The reasoning above is used regularly to shoot down some really useful > >> functionality. So what would go wrong if we chose to take the practical > >> path, and leave aside the theoretical issues? > > > > You would lose many uses of equational reasoning in your programs. Have > you > > every substituted 'x * 2' for the expression 'x + x' in one of your > programs, > > or vice versa? You can no longer do that, because someone may be > serializing > > the function you're writing, checking how it's implemented, and relying > it. > > > Yes, but it would not break any existing code. It would only break code > that knowingly did the wrong thing. > > > We already have a weak case of this, since (\x -> undefined x) can be > > distinguished from undefined using seq, but that can be hand-waved away > by not > > worrying about bottoms so much. That isn't going to work for serialize. > > Why not? > I don't know to what extent it would apply in this hypothetical situation, but ghc (and probably other compilers) rely upon Haskell's semantics in performing various code transformations. If you break the semantics some transformations become invalid, resulting in incorrect code. I've experienced this with code that violated ref. transparency. The program behavior changed depending on the compiler's optimization settings. I'm not keen to go back to that. I think the only way this would work would be if you consider functions to be equal only to themselves, i.e. "x+x" and "2*x" are not equal. That's not a trade-off I would be willing to make. John

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Fwd: Re: [Haskell-cafe] Type Directed Name Resolution
by John Lask 12 Nov '10

12 Nov '10

> On Thu, Nov 11, 2010 at 8:16 PM, John Lask<jvlask(a)hotmail.com> wrote: >> consider "length" ... >> >> I have records with the attribute length, length can be given as an Int, >> Double, Float or maybe as a constructed type "Length", length's use as a >> record selector would also clash with List.length. All these have the same >> denotation. >> >> should I then seporate into int_length, float_length, or use rec1_length, >> rec2_length etc etc... > > class Lengthy a where > type LengthType a > length :: a -> LengthType a > > This extends easily to lenses if you want setters. > to make use of the class Lengthy I still need to define record selectors with different names, which is exactly the point I am making... ....ie data Record = RecLen { rec_length :: ... } instance Lengthy Record where length = rec_length >> This is easily handled in C, Pascal, PL/1, Cobol why not in Haskell ? > > By this argument, Haskell should provide global mutable state and > allow side-effects universally. > no, but these languages have their strengths as well, for example Cobol PIC strings format currency values very nicely and it would be great if there were a Haskell library that could do the same. Not to mention currency values! The point is that languages are often constructed with a purpose in mind, at which they tend to be particularly good. Haskell has traditionally been a test bed for type system innovation, which is why we all like it so much. As and if, the usage of Haskell broadens, then domains of application stray into areas of application for which it is not ideally suited, in those circumstances why not consider features of other languages which handle those use cases well. (for some definition of "well") By the way I am not arguing for TDNR, merely that all is not well with haskell records.

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Rebindable record syntax
by Philippa Cowderoy 12 Nov '10

12 Nov '10

I stood up and suggested rebindable record syntax at Anglohaskell earlier this year, but never got round to posting a proposal. Given the TDNR discussion, it seems timely to link everyone to what I'd got round to writing: http://flippac.org/RebindableRecordSyntax.html Apologies for the lack of concrete examples: if anyone's interested I'll try to crank some out soon, specific requests would help. I probably don't have the energy to champion this properly on my own, so speak up if you think it's a good idea! Incidentally, I believe something similar has been proposed elsewhere - it's also possible I'd seen it before and forgotten before "rediscovering" the idea. -- flippa(a)flippac.org

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Fwd: Re: [Haskell-cafe] Type Directed Name Resolution
by John Lask 12 Nov '10

12 Nov '10

> > On 12/11/2010, at 2:16 PM, John Lask wrote: > >> On 12/11/2010 9:22 AM, Richard O'Keefe wrote: >>> >>> I'm afraid it's not a *convincing* use case. >>> It's not convincing because here "owner" *means different things*. >> >> >> consider "length" ... >> >> I have records with the attribute length, length can be given as an Int, Double, Float or maybe as a constructed type "Length", length's use as a record selector would also clash with List.length. All these have the same denotation. > > "All these have the same denotation"? I am extremely confused here. > AH! You mean you call them all by the same name. Well yes, that's > the problem, right there. > > I remind readers once again that in SML record selectors *don't* clash with > names of functions. I am not concerned here to argue either for or against > SML-style records and their selectors, only to point out that wanting > *record fields* whose significance depends on the record they select from > is *NOT* the same thing as TDNR in principle, so that arguments for that > don't even come close to being arguments for TDNR as such. > >> >> should I then seporate into int_length, float_length, or use rec1_length, rec2_length etc etc... > > No, the differing result types are an epiphenomenon of their differing > semantics. > > The length of a piece of string is a physical length. length of string measured in CM's, in MM, in Inches, as an Int, float ... they all denote the same thing modulo some theory. You could argue that a length in CM's measured as a float is semantically different to that of CM's as an Int, which it is, but somewhere along the line those semantic differences become irrelevant to the abstract domain of application, your model, and it is that model that you wish to represent as a program, although you need to deal with the concrete differences as an implementation detail. > The length of a lecture is a time. > The length of a queue is a natural number (counting people). > The length of a book is a positive integer (counting say pages, or words) > The length of a vowel is a relative time. > > These quantities are measured differently, combined differently, and assessed > differently. Calling them all "length" is a METAPHOR. (There are at least > three metaphors in the list above: time-is-space, codex-is-scroll, and > a form of metonomy.) > >> for proper name space management why should I have to define each record >> that defines a length field with different representation in distinct modules, or with different names for the field label when they denote the same thing? > > But you just explained that while they may have the same denotation (the > identifier), what it DENOTES is NOT the same (otherwise they could not > be different types). > you are right > As SML proves, having record-sensitive field names is a *different* > question from Type Directed Name Resolution applied to plain function names. >> agreed >> This is easily handled in C, Pascal, PL/1, Cobol why not in Haskell ? > > But it *isn't* handled *AT ALL* in any of those languages, let alone > handled easily. > > In C, Pascal, PL/I, and COBOL field names are *not* values. > C, Pascal, and PL/I let you pass functions as parameters to functions. > But you cannot pass field names that way. The only thing you can do > with a field name is apply it *immediately* to a record. And those > languages don't have type variables, so when you apply a selector to > a record, you know then and there what the type is. > > If what you want is some sort of record facility at least as good as > SML's, fine. What I am arguing against is anything resembling Type > Directed Name Resolution (alias ad hoc overloading) being applied to > plain ordinary functions. that's something like what I want. I am not argiung in favor of TDNR, only that haskell record system needs improvement, particularly the scoping of field labels. > > (By the way, if the field names of a record type are visible outside its > module, I start wondering why.) > > depends on what your using them for .. >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > >

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[ANNOUNCE] csound-expression - csound combinator library
by Anton Kholomiov 11 Nov '10

11 Nov '10

Hi, I'm glad to announce csound combinator library. It features liberation from id-style csound code, haskore-like composition structures, type-safe composable opcodes and simple instrument interface (no interface at all, instrument is just a function from some note representation to signal). http://hackage.haskell.org/package/csound-expression Anton

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build-type: configure on windows
by Nils Schweinsberg 11 Nov '10

11 Nov '10

Hi, I'm having a few problems with cabals build-type "configure" on windows, especially with the packages "curl" and "pcre-light". Both fail either with: configure: error: curl libraries not found, so curl package cannot be built Configuring pcre-light-0.4... cabal: Missing dependency on a foreign library: * Missing C library: pcre Both libraries (pcre3.dll and libcurl.dll) are in my PATH variable, and I can build other non-haskell-applications which are using these via mingws gcc compiler. But still, somehow cabal seems unable to find them. Using the recommanded "--extra-include-dirs" and "--extra-lib-dirs" won't help either. Or is cabal looking for different files than those two .dlls? Can anyone help me on this? Did anyone manage to build curl/pcre-light on windows? My current configuration is MinGW/msys with gcc 4.5, ghc 6.12.3, cabal-install 0.8.2, cabal 1.8.0.6. libcurl.dll and pcre.dll are the latest builds from the official webpages. Thanks for any Help, Nils PS: Sorry for the previous (incomplete) mail.

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Stack Overflow?
by Ben Christy 11 Nov '10

11 Nov '10

I have implemented a scene graph in Haskell and I have a problem. I walk down the scenegraph and at each node I recalculate translation matrix and pass it to each child. Well it seems to be causing a stack overflow and I am lost as to how to resolve the issue without issue a state variable of some kind to hold a "matrix stack" as is common in imperative implementations of scene graphs. When I run the program fromghci I get "drawingcamera" "drawingground" "drawinggroundModel" Matrix4x4 {i1j1 = -4.371139e-8, i1j2 = 0.0, i1j3 = 1.0, i1j4 = -3.9999998, i2j1 = 0.0, i2j2 = 1.0, i2j3 = 0.0, i2j4 = -1.5, i3j1 = -1.0, i3j2 = 0.0, i3j3 = -4.3 71139e-8, i3j4 = 3.0, i4j1 = 0.0, i4j2 = 0.0, i4j3 = 0.0, i4j4 = 1.0} "a model" "classic matrix operation" "drawingcarousel" "drawingcarouselbase" "drawingcarouselbaseModel" Matrix4x4 {i1j1 = -4.371139e-8, i1j2 = 1.0, i1j3 = -4.371139e-8, i1j4 = 0.0, i2j 1 = 0.0, i2j2 = -4.371139e-8, i2j3 = -1.0, i2j4 = 0.0, i3j1 = -1.0, i3j2 = -4.37 1139e-8, i3j3 = 1.9106855e-15, i3j4 = -1.0, i4j1 = 0.0, i4j2 = 0.0, i4j3 = 0.0, i4j4 = 1.0} "classic matrix operation" "drawingcarouselRoof" "drawingcarouselRoofModel" Matrix4x4 {i1j1 = -4.371139e-8, i1j2 = 1.0, i1j3 = -4.371139e-8, i1j4 = 0.0, i2j 1 = 0.0, i2j2 = -4.371139e-8, i2j3 = -1.0, i2j4 = 0.3, i3j1 = -1.0, i3j2 = -4.37 1139e-8, i3j3 = 1.9106855e-15, i3j4 = -1.0, i4j1 = 0.0, i4j2 = 0.0, i4j3 = 0.0, i4j4 = 1.0} "classic matrix operation" "drawingcarouselFloor" "drawingcarouselFloorModel" Matrix4x4 {i1j1 = -4.371139e-8, i1j2 = 1.0, i1j3 = -4.371139e-8, i1j4 = 0.0, i2j 1 = 0.0, i2j2 = -4.371139e-8, i2j3 = -1.0, i2j4 = 0.0, i3j1 = -1.0, i3j2 = -4.37 1139e-8, i3j3 = 1.9106855e-15, i3j4 = -1.0, i4j1 = 0.0, i4j2 = 0.0, i4j3 = 0.0, i4j4 = 1.0} "classic matrix operation" "drawingpolls" "drawingpoll1" "drawingpoll1Model" Matrix4x4 {i1j1 = <interactive>: <<loop>> <interactive>: interrupted As you can see there are only a handful of nodes at this point so I am confused as to why it is happening here, any thoughts?

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ghc dump the code for derived instances
by Ozgur Akgun 11 Nov '10

11 Nov '10

Café, Is there a way to make GHC dump the code for auto-derived type class instances, say for Show, Eq and such? Thanks, Ozgur

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