[Haskell-cafe] Re: [Haskell] thread-local variables
Furthermore, can we move this thread from the Haskell mailing list (which should not have heavy traffic) to either Haskell-Café, or the libraries list? Sure, moving to haskell-cafe. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell performance in heavy numerical computations
Alberto Ruiz has developed a linear algebra library which could be seen as an alternative to Matlab/Octave, using the GSL, ATLAS, LAPACK, etc. IIRC. http://dis.um.es/~alberto/GSLHaskell/ I've optimized it in some places, and added an interface which guarantees operand conformability through the type system at compile time. http://ofb.net/~frederik/stla/ It is almost twice as fast as Octave on an example program, and probably comparable to Matlab. However, it is currently very difficult to debug some of the type errors which are emitted by GHC when using it, and there are some outstanding heap-related bugs. Also, we don't have as wide a variety of built-in functions as Matlab and Octave do. Frederik On Thu, Jul 06, 2006 at 11:03:11PM +0100, Joel Reymont wrote: Is anyone using Haskell for heavy numerical computations? Could you share your experience? My app will be mostly about running computations over huge amounts of stock data (time series) so I'm thinking I might be better of with OCaml. Thanks, Joel -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANNOUNCE: An index-aware linear algebra library in Haskell
Hi Alberto, Those are good questions, I've added some examples which hopefully clarify the situation. Input and output of vectors is not a strong point of the library, but I don't think there is a good alternative to the way I do it. http://ofb.net/~frederik/futility/src/Vector/read-example.hs (also, your example exposed some missing functionality. I've added three new functions; in addition to listMat, now there are listMatCol, listMatRow, and listMatSquare. Hopefully these should cover almost all use cases. http://ofb.net/~frederik/futility/src/Vector/Base.hs ) By the way, here is how I would download and run the thing, although you seem to have figured it out: $ wget http://ofb.net/~frederik/futility/futility-devel.tar.gz $ tar -xvzf futility-devel.tar.gz $ cd futility-devel/ $ ghc -fth --make Vector/read-example.hs -o read-example $ ./read-example # 11.0, 23.0; 14.0, 30.0; 15.0, 33.0; 18.0, 40.0 # 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 # 1.0, 5.0; 2.0, 6.0; 3.0, 6.0; 4.0, 7.0 # # 11.0, 23.0; 14.0, 30.0; 15.0, 33.0; 18.0, 40.0 # # -3.0, -5.0; -5.0, -7.0 # # 7.0, 10.0; 15.0, 22.0 # As for your questions: Vector/examples.hs:35:11: GHC stage restriction: `x' is used in a top-level splice, and must be imported, not defined locally In the first argument of `dAM', namely `x' In the definition of `m1': m1 = $[splice](dAM x) This is a shortcoming of Template Haskell - it will not let you call a function from a splice if that function is defined in the same file as the splice. It should be possible to remove this shortcoming, but I don't know what is planned. m2 = listMat x This is not how listMat is used, see the example file above. listMat takes a list of lists and a function, and passes the matrix version of the list of lists to the function. I would also like to create a matrix from a data file: See 'v3' in the example. Cheers, Frederik On Sun, Apr 16, 2006 at 05:06:55PM +0200, Alberto Ruiz wrote: It is really counterintuitive! I will study carefully your library and the Implicit Configurations paper. Using static dimension checking we can write very solid code for matrix computations... However, I don't know how to write some definitions. For instance, this is ok: m = $(dAM [[1,2,3]]) but with: x = [[1,2,3]] :: [[Double]] m1 = $(dAM x) m2 = listMat x main = do print m1 print m2 I get: Vector/examples.hs:35:11: GHC stage restriction: `x' is used in a top-level splice, and must be imported, not defined locally In the first argument of `dAM', namely `x' In the definition of `m1': m1 = $[splice](dAM x) Vector/examples.hs:40:10: Inferred type is less polymorphic than expected Quantified type variable `m' escapes Quantified type variable `n' escapes Expected type: (v (L m, L n) - w) - t Inferred type: (forall n1 m1. (ReflectNum n1, ReflectNum m1) = v (L m1, L n1) - w) - w In the first argument of `print', namely `m2' In the result of a 'do' expression: print m2 I would also like to create a matrix from a data file: main = do let m1 = $(dAM [[1,2],[3,4::Double]]) s - readFile data.txt let list = read s :: [[Double]] --let m2 = $(dAM list) let m2 = listMat list print $ m2 * trans m1 But I get a similar error. Perhaps I must provide information about the expected dimensions, but I don't know how to do it. -- Alberto On Saturday 15 April 2006 22:09, Frederik Eaton wrote: Yes, certainly... Otherwise the library would not be much use! If it seems counterintuitive, as it did to me at first, you should check out the Implicit Configurations paper, which uses modular arithmetic as an example. My version of their code is in http://ofb.net/~frederik/futility/src/Prepose.hs The function I mainly use is: reifyIntegral :: Integral a = a - (forall s. ReflectNum s = s - w) - w which turns an integral value into a type of the ReflectNum class which represents that value, and calls the provided polymorphic function with a dummy value (actually 'undefined') of that type; then returning the function's result. Frederik On Sat, Apr 15, 2006 at 06:14:44PM +0200, Alberto Ruiz wrote: On Friday 14 April 2006 17:02, Frederik Eaton wrote: An index-aware linear algebra library in Haskell Excellent work! Is it possible to create a vector or matrix whose size is not known at compile time? -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] ANNOUNCE: An index-aware linear algebra library in Haskell
Yes, certainly... Otherwise the library would not be much use! If it seems counterintuitive, as it did to me at first, you should check out the Implicit Configurations paper, which uses modular arithmetic as an example. My version of their code is in http://ofb.net/~frederik/futility/src/Prepose.hs The function I mainly use is: reifyIntegral :: Integral a = a - (forall s. ReflectNum s = s - w) - w which turns an integral value into a type of the ReflectNum class which represents that value, and calls the provided polymorphic function with a dummy value (actually 'undefined') of that type; then returning the function's result. Frederik On Sat, Apr 15, 2006 at 06:14:44PM +0200, Alberto Ruiz wrote: On Friday 14 April 2006 17:02, Frederik Eaton wrote: An index-aware linear algebra library in Haskell Excellent work! Is it possible to create a vector or matrix whose size is not known at compile time? - Due to the need to specify index types at some point, input of vectors is difficult. I have provided two functions in Fu.Vector.Base which should cover most of the cases: listVec :: Vector v e = [e] - (forall n . (ReflectNum n) = v (L n) - w) - w listMat :: Vector v e = [[e]] - (forall n m . (ReflectNum n, ReflectNum m) = v (L m, L n) - w) - w However, these aren't useful in interactive situations. So I have also provided some template-haskell routines http://ofb.net/~frederik/futility/src/Vector/Template.hs which can be used to instantiate vectors directly. For example: (In examples.hs): -- matrix with elements of type Double v6 = trans $(dAM [[1,2,3,4]]) v7 = $(dAM [[1,0,0],[0,1,0],[0,0,1],[1,1,1]]) -- Alberto -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: generics question 2
Hi Ralf, Thanks. I'm sorry, now I think that wasn't the source of my problem. What I want to do is specialise not to a specific type like Bool but to the class of all pairs (a,b). But this causes the compiler to complain, even for simpler examples: cast True :: (Typeable a, Typeable b) = Maybe (a,b) interactive:1:0: Ambiguous type variable `a' in the constraints: `Typeable a' arising from instantiating a type signature at interactive:1:0-51 `Show a' arising from use of `print' at Top level Probable fix: add a type signature that fixes these type variable(s) interactive:1:0: Ambiguous type variable `b' in the constraints: `Typeable b' arising from instantiating a type signature at interactive:1:0-51 `Show b' arising from use of `print' at Top level Probable fix: add a type signature that fixes these type variable(s) Is there a way to solve this, or do I have to avoid polymorphism? I can use 'toConstr' to find out dynamically if a particular type is a pair, and then use unsafeCoerce, but I hear that unsafeCoerce is unsafe. Frederik On Mon, Apr 03, 2006 at 05:41:55PM -0700, Ralf Lammel wrote: Hi Ralf, I'm looking for a function like extT but with more general type: (t a - s a) - (t b - s b) - (t a - s a) Is there such a thing in the generics library? Hi Frederik, Not sure how you are exactly going to use such an operation ... But here is its implementation anyhow. Thanks for the riddle. Ralf import Data.Generics -- Frederik's weird ext operation :-) ext' :: (Data (t a), Data (s a), Data (t b), Data (s b)) = (t a - s a) - (t b - s b) - (t a - s a) ext' f g ta = case cast g of Just g' - g' ta Nothing - f ta -- A generic default f (Just x) = [x] f Nothing = [] -- A type-specific case g (Just True) = [True] g (Just False) = [] g Nothing = [] -- A composition using our new type-extension operator test :: Data a = Maybe a - [a] test = ext' f g -- Let's see whether it works ... main = do print $ test (Just (1::Int)) print $ test (Just False) -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] generics question 2
Hi Ralf, I'm looking for a function like extT but with more general type: (t a - s a) - (t b - s b) - (t a - s a) Is there such a thing in the generics library? Thanks, Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] matrix computations based on the GSL
Hi Alberto, I'm sorry if this has been discussed before... I'm reading your paper, at one point it says (re. the PCA example): Octave achieves the same result, slightly faster. (In this experiment we have not used optimized BLAS libraries which can improve efficiency of the GSL) That seems to imply that there is a way to use optimized BLAS libraries? How can I do that? Also, in my experiments (with matrix inversion) it seems, subjectively, that Octave is about 5 or so times faster for operations on large matrices. Presumably you've tested this as well, do you have any comparison results? Thanks, Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] STUArray
I see. The solutions on that thread, i.e.: http://www.mail-archive.com/haskell%40haskell.org/msg17085.html would seem to require me to at least declare an instance of some class, for every type that I want to support. So the short answer to I'm trying to figure out how to use STUArray. Is it possible to let it be polymorphic? appears to be No. Perhaps some sort of warning in the documentation for STUArray is in order, until Bulat's code can be incorporated? By the way, why make the distinction between unboxable types and other types in the first place? E.g., just because I want something to work quickly on Int, doesn't mean that I don't want it to work at all on String. It seems that there could be a default IArray UArray e instance which just implements a regular Array behind the scenes. Frederik On Fri, Mar 10, 2006 at 11:49:10PM +0100, Benjamin Franksen wrote: On Friday 10 March 2006 23:01, Frederik Eaton wrote: I'm trying to figure out how to use STUArray. Is it possible to let it be polymorphic? Hi Frederik I think this thread (and the one it referres to) provide a solution: http://www.mail-archive.com/haskell%40haskell.org/msg17081.html Ben -- There are three kinds of programmers: those who make off by one errors, and those who don't. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] STUArray
Hi all, I'm trying to figure out how to use STUArray. Is it possible to let it be polymorphic? Here is an excerpt from my program: class (IArray UArray k, Ord k, Fractional k) = Elt k class (Bounded a, Enum a, Ix a, Eq a, Show a) = IxB a -- |like Array but uses IxB instead of Ix newtype Vector k i = Vector (UArray.UArray i k) deriving (Eq) margin :: (IxB a, IxB b, Elt k, (MArray (STUArray s) k (ST s))) = Vector k a - (a - b) - Vector k b margin (Vector v) f = Vector (runSTUArray (do ax - newArray (minBound, maxBound) 0 mapM_ (\ (i,x) - updateArray ax (f i) (+x)) (assocs v) return ax )) where updateArray ax i f = do e - readArray ax i writeArray ax i (f e) When I try to run it, I get the following error. I think I understand what the error means, but not how to fix the problem: Vector2.hs:166:22: No instance for (MArray (STUArray s) k (ST s)) arising from use of `updateArray' at Vector2.hs:166:22-32 Probable fix: add (MArray (STUArray s) k (ST s)) to the expected type of an expression or add an instance declaration for (MArray (STUArray s) k (ST s)) In a lambda abstraction: \ (i, x) - updateArray ax (f i) ((+ x)) In the first argument of `mapM_', namely `(\ (i, x) - updateArray ax (f i) ((+ x)))' In a 'do' expression: mapM_ (\ (i, x) - updateArray ax (f i) ((+ x))) (assocs v) Thanks in advance, Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] matrix computations based on the GSL
Hi, I've just looked through this discussion, since I'm working on my own library, I wanted to see what people are doing. It's something like this, using the Prepose (Implicit Configurations) paper: data L n = L Int deriving (Show, Eq, Ord) -- singleton domain type S = L Zero class (Bounded a, Ix a) = IxB a instance ReflectNum n = Bounded (L n) where minBound = L 0 maxBound = L $ reflectNum (__ :: n) - 1 mul :: (Num k, IxB a, IxB b, IxB c) = Matrix k a b - Matrix k b c - Matrix k a c add :: (Num k, IxB a, IxB b) = Matrix k a b - Matrix k a b - Matrix k a b vec :: (Num k, IxB a, IxB b) = Matrix k a b - Matrix k (a,b) S This way one can form a type L n which represents integers between 0 inclusive and n (rather, 'reflectNum (__ :: n)') exclusive, which can serve to index the matrices and vectors... Of course, other index types are allowed, such as Either a b - if we want to, say, take the sum of two vector spaces, one indexed by a and the other by b, then the result should be indexed by Either a b, etc. - we never have to do anything with the type-level numerals other than assert equality, i.e. we don't have to be able to add or multiply them in our type-signatures, since structural operations will suffice. I think having the ability to guarantee through the type system that column and row dimensions are correct is of paramount importance to those who would use a matrix library, but so far in this thread I haven't seen any suggestions which would accomplish that. I'm sorry if I didn't read carefully. Does my approach not work? I haven't filled in the implementation yet, but it type-checks. Frederik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to debug GHC
On Mon, Sep 19, 2005 at 02:22:10PM +0100, Glynn Clements wrote: Frederik Eaton wrote: In addition to the stack trace problems, I found: (1) a problem where output freezes when it is being piped through 'tee' and the user presses ^S and then ^Q That's the terminal driver; use stty -ixon to disable that. That will sure prevent ^S and ^Q having any effect, but it won't make the bug go away. With other programs, e.g. if I run seq 10 | tee foo and press ^S and then ^Q, then suspend and resume work as expected, there is no freezing shortly after resume as I am observing with my ghc-compiled program. The program should resume its output when ^Q is pressed, rather than freezing. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generics question, logical variables
Hi Ralf, I'm revisiting this project and just have another question. The story seems to be that GHC cannot derive Typeable1, or Typeable when Typeable1 is available - so anyone who wants to use ext1Q must define special instances for all of the datatypes they use, is this correct? Will this change soon? Aside from that, your 'idify' in PseudoFmap2 certainly seems to have the correct type for this application. However, the absence of automatic derivation is somewhat of an impediment. Thanks for your help. Frederik On Tue, Aug 30, 2005 at 02:25:08PM -0700, Ralf Lammel wrote: Frederik, As for your code example, it looks very interesting, but are you saying that this could turn into an extension of the Data.Generics library, or that this is something I could be implementing in terms of what's already there? The posted code works with GHC 6.4 (SYB2) intentionally and actually. I have attached another attempt (again GHC 6.4, based on SYB2) which might be more useful for your purposes, and it may be useful in general, in fact. What I defined this time is a certainty-improving function: idify :: (Typeable1 f, Monad m, Data (a f), Data (a Id)) = (forall a. f a - m a) - a f - m (a Id) That is, the function idify get takes a value whose type is parameterized in a type constructor f (such as Maybe or IORef), and the function attempts to establish Id instead of f on the basis of the function argument get. What is the 'a' parameter for in force? force :: ( Data (t Maybe a) , Data (t Id a) , Term t Maybe a , Term t Id a ) = t Maybe a - t Id a The previous attempt was a more parameterized blow than required in your case. (I was guessing about what typed logical variables could mean. I was assuming that you would need some extra layer of embedding types on top of the Haskell term types. Looking at your code, this was not the case.) For the part which I asked for help with, to get around my trouble with generics, I defined a class GenFunctor and an example instance. The intent is that generics should be able to provide this functionality automatically later on, but you can see what the functionality is. Let's look at the type of your GenFunctor: class GenFunctor f where gfmapM :: (Monad m, FunctorM b) = (forall x . a x - m (b x)) - f a - m (f b) This type can be seen as a more relaxed version of the idify operation above. That is, idify fixes GenFunctor's b to Id. The particular encoding of idify (attached) takes advantage of this restriction. I wonder whether I should bother. (Exercise for reader :-)) However, I am stuck on something else, the program doesn't typecheck because of use of another function I defined, 'cast1'. Maybe you can take a look. I had thought that I would be able to write a generic 'unify' but I get the error: GenLogVar.hs:82:19: Ambiguous type variable `a' in the constraint: `Data a' arising from use of `cast1' at GenLogVar.hs:82:19-23 Probable fix: add a type signature that fixes these type variable(s) This is because I need to do something special when I encounter a Var variable in unification, but the compiler seems to not like the fact that the type argument of the Var data type is not known. Please try to avoid new cast operations at all costs. :-) Your code can be arranged as follows: (i) Use extQ1 to dispatch to a special case for Var x for the first argument. (ii) In this special case, use again ext1Q to dispatch to a special case for Var y for the second argument. (iii) At this point, *cast* the variable value of *one* variable to the type of the other. So the problem with your code, as it stands, is that the target type of cast is ambiguous because you cast *both* arguments. The insight is to make the cast asymmetric. Then, not even polymorphism is in our way. Interesting stuff! Ralf -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to debug GHC
It could be a bug - can you reduce the example and report it? GHC's profiler tries to overlay a lexical call graph on to the dynamic execution of the program. It does this more or less in the way you described before: every function gets an extra argument describing the call context. However, there are some tricky areas: notably CAFs. We don't as yet have a principled description of the mechanism, and I know of various cases where odd results are obtained with the current system. Also, the optimiser has to be careful not to change the shape of the call graph, and I suspect there are cases where it goes wrong. I see. Well, I'm afraid I've lost the example, but I'll keep my eyes open in case it happens again. It's good to know what the correct behavior is supposed to be. While I was finishing a project for somebody I ran into this problem again, as well as some other bugs, and made several copies of the code so that the problems could be reproduced. In addition to the stack trace problems, I found: (1) a problem where output freezes when it is being piped through 'tee' and the user presses ^S and then ^Q and (2) an issue where a trace statement is not being printed correctly by ghc (but is being printed correctly by runghc). However, I don't have time to reduce these to minimal test cases. Do you want to look at them anyway? Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to debug GHC
On Wed, Sep 14, 2005 at 02:44:11PM +0100, Simon Marlow wrote: On 10 September 2005 21:15, Frederik Eaton wrote: On Fri, Sep 02, 2005 at 04:40:05PM +0400, Bulat Ziganshin wrote: Hello Nils, Friday, September 02, 2005, 10:47:05 AM, you wrote: Compile your program with -prof -auto-all (make sure you have the I tried this out under GHC 6.4/Linux and got a segmentation fault instead of a stack trace. Under GHC 6.2.2 it seemed to work, though. this error is already fixed in current pre-6.4.1 version I'm using a 2005/9/3 version of 6.4.1 and running into situations where the stack trace has function A calling function B, where when I look at the code, A never calls B. Is this normal? Is it some side-effect of laziness? It sure makes the traces a lot less useful. It could be a bug - can you reduce the example and report it? GHC's profiler tries to overlay a lexical call graph on to the dynamic execution of the program. It does this more or less in the way you described before: every function gets an extra argument describing the call context. However, there are some tricky areas: notably CAFs. We don't as yet have a principled description of the mechanism, and I know of various cases where odd results are obtained with the current system. Also, the optimiser has to be careful not to change the shape of the call graph, and I suspect there are cases where it goes wrong. I see. Well, I'm afraid I've lost the example, but I'll keep my eyes open in case it happens again. It's good to know what the correct behavior is supposed to be. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to debug GHC
Just more or less as an aside, at its origin in April (!) this thread didn't mention any debugger - the question was just how to build ghc so that a stack trace would come out. A real debugger is no replacement for that (because you have to be on hand and know how to repeat the problem to get anywhere with a debugger), but that's just my opinion. Donn Cave, [EMAIL PROTECTED] I agree. Some could argue that stack traces are no replacement for a debugger but it is also true that a debugger is no replacement for stack traces. :) I will try the +RTS -xc -RTS method, many thanks to everybody for the advice. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to debug GHC
On Wed, Apr 27, 2005 at 05:15:30PM +1000, Bernard Pope wrote: On Wed, 2005-04-27 at 07:45 +0200, Ketil Malde wrote: [I want to know] who called who all the way from main to head, because the key function is going to be one somewhere in the middle. Perhaps. I am told stack backtraces are difficult with non-strict semantics. This is true, at least for _lazy_ implementations of non-strict semantics. The reason is that the (graph) context in which a function application is constructed can be very different to the context in which it is reduced. Is it that backtraces are difficult, or just require a lot of overhead? It doesn't seem very hard to me, at least in principle. Add a stack trace argument to every function. Every time a function is called, the source location of the call is prepended to the stack trace. I'm not familiar with the implementation of functional programming languages, though. (It seems like if the operation of GHC or GHCI could be parametrized by an arbitrary monad, here a Reader, then transformations like the above wouldn't be so difficult, and compiler compatibility for debuggers wouldn't be so much of an issue.) Partial application of functions introduces a similar problem. This is not a problem in first-order eager languages because the construction of a (saturated) function application is followed immediately by its reduction. Thus the contexts of construction and reduction are the same. Debugging tools like Hat, Freya and Buddha, remember the construction context of an application, so you can get call graphs that reflect the dependencies between symbols in the source code. Thus you can construct a meaningful backtrace etc. Actually, Hat remembers quite a bit more context than Freya and Buddha, but that's another story. Are the following correct? 1. Hat requires users to restrict themselves to a certain small subset of the standard libraries, and to use hmake 2. Buddha doesn't work with GHC 6.4 3. I can't find Freya 4. I can't find HsDebug. Maybe it's part of the fptools cvs repository? But solander.dcs.gla.ac.uk seems to be down :( But getting a stack backtrace when there is an error should be a pretty basic feature. It's very hard to debug a large program when you can randomly get messages like *** Exception: Prelude.head: empty list and have no idea where they came from. So GHC's many features become much less useful when there is no debugger which supports a program that has been written with them. Furthermore, in my opinion, this sort of error location information is much more valuable to debugging a program, than being able to step through its execution, which is the more difficult problem that a lot of the debuggers seem to be aimed at solving. So maybe it would be good if GHC had basic stack trace support built in? It could be a compiler option, which would produce slower but more debuggable code... Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generics question, logical variables
strong typing. - We make the assumption that all occurrences of Spot are to be converted. - That is, we don't quite track the type parameter for Maybe vs. Id. - This is a bit inefficient because of going through Tree Constr. So I am willing to summarize that this is potentially a sort of a (cool) hack. Code attached. Ralf P.S.: The extension you propose seems to be a major one. Perhaps you could look into the TH code for SYB3 (ICFP 2005) to see whether this can be automated. This sort of discussion calls for kind polymorphism once again. -Original Message- From: [EMAIL PROTECTED] [mailto:haskell-cafe- [EMAIL PROTECTED] On Behalf Of Frederik Eaton Sent: Sunday, August 28, 2005 9:36 PM To: haskell-cafe@haskell.org Subject: [Haskell-cafe] generics question, logical variables Hi all, I'm trying to write something like a generic fmap, or a generic natural transformation. The application is this. I have a typed logical variable library which produces arbitrary terms with values of type Var a, which are references to a value of type Maybe a, and I want to write a solve function which replaces these values with instantiated versions of type Id a where newtype Id a = Id a . Furthermore I want this to be reflected in the type of the generic term: solve :: Pred (t Var) - [t Id] so if I have a type like data Entry k = Entry (k String) (k Int) then I can write some constraint equation with values of type Entry Var, and get back values of type Entry Id - in other words, objects where the unknowns are statically guaranteed to have been filled in. I looked at the generics library. I may be mistaken, but it seems that it doesn't have what I need to do this. The problem isn't the mapping, it's creating a new type which is parameterized by another type. The only options for creating new types are variations on fromConstr :: Data a = Constr - a but what is needed is something like fromConstr1 :: Data1 a = Constr1 - a b With something like that it should be possible to define: gmapT1 :: (forall b . Data1 b = b l - b m) - a l - a m Does this make sense? Here I would be treating all instances of Data as possibly degenerate instances of Data1 (which just might not depend on the type variable). If it seems like a good idea, I would be interested in helping out with the implementation. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] generics question, logical variables
Hi all, I'm trying to write something like a generic fmap, or a generic natural transformation. The application is this. I have a typed logical variable library which produces arbitrary terms with values of type Var a, which are references to a value of type Maybe a, and I want to write a solve function which replaces these values with instantiated versions of type Id a where newtype Id a = Id a . Furthermore I want this to be reflected in the type of the generic term: solve :: Pred (t Var) - [t Id] so if I have a type like data Entry k = Entry (k String) (k Int) then I can write some constraint equation with values of type Entry Var, and get back values of type Entry Id - in other words, objects where the unknowns are statically guaranteed to have been filled in. I looked at the generics library. I may be mistaken, but it seems that it doesn't have what I need to do this. The problem isn't the mapping, it's creating a new type which is parameterized by another type. The only options for creating new types are variations on fromConstr :: Data a = Constr - a but what is needed is something like fromConstr1 :: Data1 a = Constr1 - a b With something like that it should be possible to define: gmapT1 :: (forall b . Data1 b = b l - b m) - a l - a m Does this make sense? Here I would be treating all instances of Data as possibly degenerate instances of Data1 (which just might not depend on the type variable). If it seems like a good idea, I would be interested in helping out with the implementation. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal --user question
Hi Isaac, Is there a way to specify a particular package.conf for use when installing and registering packages with Cabal? I'm trying to Cabal-ize WASH which has a number of packages which depend on each other. The problem is that in order to build the next package, the previous one has to be installed, yet users typically want to do a full build *before* installing anything. I was thinking that for the 'make' step it could just install each package locally and register it in a local package.conf (i.e. somewhere in the project tree), and then 'make install' would rerun the install commands with the final install location and final package database as arguments. But I can't figure out how to specify the local package.conf to 'configure' or 'install', there are just the '--user' and '--global' commands which aren't quite enough. Frederik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal --user question
Hi, How do I install a package in the user package.conf with cabal? It is not clear to me how to do this, looking at the output of 'configure --help'. There is an option --user to get dependencies from the user cabal file but this still, somewhat counterintuitively, tries to install the package in the global location (why would one want such behavior?). Specifying '--with-hc-pkg=ghc-pkg --user' doesn't seem to work either, when I do this then 'install' and 'unregister' complete without error but apparently have no effect. Thanks in advance, Frederik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal --user question
Thanks for the quick reply! How do I install a package in the user package.conf with cabal? It is not clear to me how to do this, looking at the output of 'configure --help'. There is an option --user to get dependencies from the user cabal file but this still, somewhat counterintuitively, tries to install the package in the global location (why would one want such behavior?). Specifying '--with-hc-pkg=ghc-pkg --user' doesn't seem to work either, when I do this then 'install' and 'unregister' complete without error but apparently have no effect. ./setup configure --user #if it depends on user-local packages ./setup build ./setup install --user Ah, I see. Perhaps install --user should be the default if you configure --user. Yeah, it seems somewhat inconsistent - everything about the installation of a package is usually controlled by 'configure' options (e.g. in autoconf), even in cabal the prefix is still part of 'configure' but the other relevant installation parameter is specified as an option to 'install'... For one, it means that I can't just call ./setup unregister to unregister my package, I have to remember which arguments I passed to 'register' or 'install'. It seems like a bad design to me. At the very least, I should be able to specify the default behavior (user or global) at configure time so that if I run these commands without arguments they behave in a way that is consistent with each other and with the package configuration. Is there a reason why there is no 'uninstall' command, by the way? It might be useful. Also, I would shorten the '--copy-prefix' argument to 'copy' to just '--prefix' unless there is a good reason for having it that way. The copy- part seems reduntant to me. That's my opinion. The user's guide is here: http://www.haskell.org/ghc/docs/latest/html/Cabal/ Thanks, Frederik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal --user question
I forgot to say, when I run configure like runghc Setup.hs configure --with-hc-pkg=ghc-pkg --user --prefix=$HOME and then run 'install', it exits with code 127 but displays no error message. Maybe something to look into... Frederik On Sun, Jul 10, 2005 at 05:00:13PM -0700, Frederik Eaton wrote: Thanks for the quick reply! How do I install a package in the user package.conf with cabal? It is not clear to me how to do this, looking at the output of 'configure --help'. There is an option --user to get dependencies from the user cabal file but this still, somewhat counterintuitively, tries to install the package in the global location (why would one want such behavior?). Specifying '--with-hc-pkg=ghc-pkg --user' doesn't seem to work either, when I do this then 'install' and 'unregister' complete without error but apparently have no effect. ./setup configure --user #if it depends on user-local packages ./setup build ./setup install --user Ah, I see. Perhaps install --user should be the default if you configure --user. Yeah, it seems somewhat inconsistent - everything about the installation of a package is usually controlled by 'configure' options (e.g. in autoconf), even in cabal the prefix is still part of 'configure' but the other relevant installation parameter is specified as an option to 'install'... For one, it means that I can't just call ./setup unregister to unregister my package, I have to remember which arguments I passed to 'register' or 'install'. It seems like a bad design to me. At the very least, I should be able to specify the default behavior (user or global) at configure time so that if I run these commands without arguments they behave in a way that is consistent with each other and with the package configuration. Is there a reason why there is no 'uninstall' command, by the way? It might be useful. Also, I would shorten the '--copy-prefix' argument to 'copy' to just '--prefix' unless there is a good reason for having it that way. The copy- part seems reduntant to me. That's my opinion. The user's guide is here: http://www.haskell.org/ghc/docs/latest/html/Cabal/ Thanks, Frederik ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] tuple and HList
You need to swap the arguments to TCons... data TCons l a = TCons !l a Then: instance Functor (TCons (TCons HNil a)) where fmap f (TCons (TCons HNil x) y) = TCons (TCons HNil (f x)) y) How does one solve this problem in general, i.e. when the arguments to a type are in the wrong order for an instance that one wants to declare? Someone on the haskell IRC channel mentioned that if you could derive instances for partially applied type synonyms then one could just make a dummy synonym with the arguments in the right order, but that doesn't appear to be premitted. The other question is why isn't it permitted. Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] tuple and HList
This was brought up in passing in a recent conversation on haskell-cafe Sorry, mairix was malfunctioning... It certainly seems like an interesting idea, Would type inference still work okay? I don't understand all of the issues. One is that in the HList paper, rather than constructing HLists with data constructors, they use special functions which guarantee through class constraints that the tail of an HList is a valid HList, and not some other random type. (There was some reason that they didn't want to put the constraints on the data type itself.) But this prevents us from using the same syntax in construction and pattern matching. And if tuples were syntactic sugar for something that constructs a valid HList then it seems the constraints wouldn't be necessary. The other problem mentioned is that they are not quite isomorphic, since HLists are equivalant to (a,(b,c)) rather than (a,b,c), but changing HCons so that it is strict in its second argument makes them behave the same I think.. And it's important to be able to costruct a HList with one element. Perhaps the syntax (a,) could be used for a tuple with one element? Since most of the HList functionality is defined using type classes, we could probably declare a new type, TCons, make it strict in the second argument, and use it alongside HCons. data TCons a b = TCons a !b One way t make tuples into sugar for HLists would be to effectively have a series of declarations like these: type (a,b) = TCons a (TCons b HNil) type (a,b,c) = TCons a (TCons b (TCons c HNil)) But then we can't use tuples in instance declarations. That is, there isn't any way to desugar 'instance Functor ((,) a)' without using a type lambda. I'm not sure I understand this, but the intent was that you'd use e.g. TCons instead of the tuple syntax in instance declarations. On the other hand, using HLists for tuples means we can have projection functions that work on any tuple arity, which would be nice. Another thing which I don't think is mentioned in the paper, which is convenient, is that you can define HLists all of whose elements are members of a given class: class HListShow l instance HListShow HNil instance (Show a, HListShow l) = HListShow (a :* l) It's not as clean as if you could parameterize over classes, but it's better than this... (Show a, Show b) = Show (a, b) (Show a, Show b, Show c) = Show (a, b, c) (Show a, Show b, Show c, Show d) = Show (a, b, c, d) (Show a, Show b, Show c, Show d, Show e) = Show (a, b, c, d, e) Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] tuple and HList
That's a neat technique. Since it's so general it would be nice if there were a way to make it more automatic, could one use template haskell? It seems one should be able to write HListConstraint $(mkConstraint Show) l to generate the declarations automatically. Frederik On Sun, Mar 20, 2005 at 11:05:06PM +, Keean Schupke wrote: Frederik Eaton wrote: Another thing which I don't think is mentioned in the paper, which is convenient, is that you can define HLists all of whose elements are members of a given class: class HListShow l instance HListShow HNil instance (Show a, HListShow l) = HListShow (a :* l) You can avoid the need to declare a new class for each constrained list by using the following: class Constraint c a data SHOW instance Show a = Constraint SHOW a class HListConstraint c l instance HListConstraint c HNil instance (Constraint c a,HListConstraint c l) = HListConstraint c (HCons a l) You can now constrain a list as follows: assertShow :: HListConstraint SHOW l = l - l assertShow = id The type parameter can be made first class using: showConstraint :: SHOW showConstraint = undefined So we can now pass this as a parameter: assertConstraintOnHList :: HListConstraint c l = c - l - l assertConstraintOnHList _ = id Keean. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] tuple and HList
HList seems just like a tuple, but more powerful because one can access the type structure directly, and more cumbersome because one has to use lengthier constructors a 'nil' terminator. So why not just make tuples synonyms for HLists, so one can use HLists with the shorter notation, and have the added benefit of being able to access the internals of a tuple (e.g. make instances which concatenate generic tuples, project elements, etc.)...? Frederik -- http://ofb.net/~frederik/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
