Re: [Haskell-cafe] What is a simple pattern binding?
At Sun, 26 Jun 2011 01:41:01 +0100, Paterson, Ross wrote: I thought no type signature meant no type signature inside b1. No, it means no type signature for the variable. Otherwise, you are saying nothing could depend on a binding with a type signature. By that logic, there can be no mutual dependence, and so every declaration with a type signature is its own (singleton) declaration group. A pattern binding can bind more than one variable. If all the variables bound by a binding have type signatures, that binding is indeed a singleton declaration group. If this is the case, then multiple sentences in the 2010 report don't make sense, though the way in which they don't make sense sort of depends on what simple pattern binding means. Which of the following constitute a simple pattern binding? a. a | False = undefined | otherwise = \x - x b. Just b = Just (\x - x) c. Just c | False = undefined | otherwise = Just (\x - x) d. (d, d') = (\x - x, d) e. (e, e') | False = undefined | otherwise = (\x - x, e) If it's any clue, GHC infers a polymorphic type for a only. It infers type GHC.Prim.Any - GHC.Prim.Any for the others. Moreover, GHC accepts the type signature a :: t - t, but rejects such a polymorphic signature for the other variables, and also rejects programs such as: Just b = Just (\x - x) f :: (Show a) = a - a f = b -- illegal So let's work under the assumption that a is a simple pattern binding, and the others are not. If you have a different definition, I'll make a different argument. (Note also that if you agree with this definition, then there is a bug in section 4.4.3.2 of the report, since a is not of the form p = e. But if you take the 4.4.3.2 definition, then I'll argue section 4.5.5 has a bug.) Let's posit a definition that accepts only a (and in particular that rejects d and e). Such a definition is further supported by the phrase a simple pattern binding is a pattern binding in which the pattern consists of only a single variable (from section 4.5.5). If we accept that a simple pattern binding cannot bind more than one variable, then the definition of the monomorphism restriction in section 4.5.5 is not consistent with your interpretation of the term declaration group. After all, given our posited definition, the following language in 4.5.5: (a): every variable in the group is bound by a function binding or a simple pattern binding (Section 4.4.3.2), and (b): an explicit type signature is given for every variable in the group that is bound by simple pattern binding. should instead read: (a): every binding is a function binding, or (b): the group consists of a simple pattern binding with an explicit type signature. In particular, why would the report say an explicit type signature is given for EVERY variable when there can be only one such variable? David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Can't use libraries in haskell
Hello, I'm new in haskell. I want to use xml library (http://hackage.haskell.org/package/xml) in my project. I downloaded it.then try to build and install: runhaskell Setup.hs configure runhaskell Setup.hs build runhaskell Setup.hs install All ok. There are no errors. When i try import modules from this lib to my project, for example: import Text.XML.Light.Cursor I get error: /home/shk/dev/src/XMPP.hs:8:8: Could not find module `Text.XML.Light.Cursor': Use -v to see a list of the files searched for. Failed, modules loaded: none. if i try: cabal install xml Resolving dependencies... No packages to be installed. All the requested packages are already installed. If you want to reinstall anyway then use the --reinstall flag. What's wrong? How can i install and use library in haskell? Thank you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't use libraries in haskell
What's wrong? How can i install and use library in haskell? First thing is to do 'ghc-pkg list'. If your package doesn't show up then it's not installed, according to the package registry. 'cabal install' should have registered it. If it is in the list, then it depends how you're building. If you use ghc manually, then you have to give '-package xyz'. If you use 'ghc --make', ghc will automatically add the -package for you. If you use cabal, you put the package in the dependencies, and 'cabal build' will add -package for you. If the package has parens, then someone hid it, and you'll have to do 'ghc-pkg expose' on it. If you're doing everything else right and it still doesn't find the package, then you can run ghc -v and it'll print lots of details. It might have something about 'hiding xyz because of some version thing', which means you're depending on libraries that expect different versions of the underlying library. You can sometimes get out of this by carefully upgrading or downgrading certain libraries. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't use libraries in haskell
Thank you, for reply. Yes i use ghc. First thing is to do 'ghc-pkg list'. If your package doesn't show up then it's not installed, according to the package registry. 'cabal install' should have registered it. If it is in the list, then it depends how you're building. If you use ghc manually, then you have to give '-package xyz'. If you use 'ghc --make', ghc will automatically add the -package for you. If you use cabal, you put the package in the dependencies, and 'cabal build' will add -package for you. If i want to use ghci to test any function from my project. How can i import lib then? Thank you. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is a simple pattern binding?
If this is the case, then multiple sentences in the 2010 report don't make sense, though the way in which they don't make sense sort of depends on what simple pattern binding means. Indeed, the Report has two problems: Sections 4.4.3.2 and 4.5.5 have different definitions of simple pattern. This has been there since section 4.5.5 (Monomorphism Restriction) was added in Haskell 1.1. But then the only technical use of the term is in section 4.5.5. When the definition of declaration group (section 4.5.1) was changed in Haskell 2010 to break dependencies on type signatures, Rule 1 of the Monomorphism Restriction (section 4.5.5), while not incorrect, became partially redundant and overly complex. It could have been simplified along the lines you describe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alex Lexer Performance Issues
On 22 Jun 2011, at 15:53, Tristan Ravitch wrote: On Wed, Jun 22, 2011 at 07:48:40AM +0100, Stephen Tetley wrote: How fast is good old String rather than ByteString? For lexing, String is a good fit (cheap deconstruction at the head / front). For your particular case, maybe it loses due to the large file size, maybe it doesn't... I gave it a shot and the percentages in the profile are approximately the same (and peak memory usage was about double). I might end up having to parse the original binary format instead of the text format. There is an old folklore that lexing is usually the most expensive phase of any compiler-like traversal. 50% of time and space expended on lexing was pretty common twenty years ago. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Time
On 26 Jun 2011, at 01:53, Tony Morris wrote: Having only had a flirt with Data.Time previously, I assumed it would be robust like many other haskell libraries. If, by lack of robustness, you mean that you get runtime errors, then consider them bugs, and file them with the author/maintainer accordingly. If you mean something else, then being more specific might be useful. I know that the first time I looked seriously at Data.Time it seemed rather byzantine and labyrinthine. So many types! So few direct conversions between them! But when you think more closely about the domain, you realise that notions of time are not simple at all, and have varied widely over history, and the complexity of Data.Time only reflects the complexity of the domain. The old-time package is still available, and has a much simplified approach to time (which is evidently wrong in many places), but may better suit the needs of applications that only care to be approximate. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] commutative monoid?
On Sat, Jun 25, 2011 at 02:34:47PM -0700, Evan Laforge wrote: On Sat, Jun 25, 2011 at 2:02 PM, Brent Yorgey byor...@seas.upenn.edu wrote: Actually, there are (at least) four: there's also the one where mappend = liftA2 mappend, i.e. introduce potential failure into a monoid operation defined on the values. I wrote about it here: http://byorgey.wordpress.com/2011/04/18/monoids-for-maybe/ Just out of curiosity, what was the problem that wanted this kind of monoid for the solution? I always find concrete examples useful in addition to the abstract explorations and toy examples. To be honest, I don't remember! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Period of a sequence
MathWorks has the function seqperiod(x) to return the period of sequence x. Is there an equivalent function in Haskell? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't use libraries in haskell
2011/6/26 Александр kommunist1...@mail.ru: Thank you, for reply. Yes i use ghc. First thing is to do 'ghc-pkg list'. If your package doesn't show up then it's not installed, according to the package registry. 'cabal install' should have registered it. If it is in the list, then it depends how you're building. If you use ghc manually, then you have to give '-package xyz'. If you use 'ghc --make', ghc will automatically add the -package for you. If you use cabal, you put the package in the dependencies, and 'cabal build' will add -package for you. If i want to use ghci to test any function from my project. How can i import lib then? I find this is easiest with cabal-dev. Here is a guide to using cabal-dev: http://www.reddit.com/r/haskell/comments/f3ykj/psa_use_cabaldev_to_solve_dependency_problems/ When I want to test out a library in ghci I do the following: mkdir -p ~/tmp/test-foo cd ~/tmp/test-foo cabal-dev install foo cabal-dev ghci That puts me in ghci with the newly installed foo available so then you just type, :m + Data.Foo, or in recent ghci you can even type import Data.Foo. I hope that helps, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is a simple pattern binding?
At Sun, 26 Jun 2011 09:31:05 +0100, Paterson, Ross wrote: Indeed, the Report has two problems: Sections 4.4.3.2 and 4.5.5 have different definitions of simple pattern. This has been there since section 4.5.5 (Monomorphism Restriction) was added in Haskell 1.1. But then the only technical use of the term is in section 4.5.5. When the definition of declaration group (section 4.5.1) was changed in Haskell 2010 to break dependencies on type signatures, Rule 1 of the Monomorphism Restriction (section 4.5.5), while not incorrect, became partially redundant and overly complex. It could have been simplified along the lines you describe. Aha! This is starting to make sense! Indeed the Haskell98 text is far clearer, and when I look at the differences in section 4.5.1, I start to understand what the committee meant. Still, the clause b1 contains a free identifier that has no type signature and is bound by b2 applies the phrase has no type signature to the identifier, not to the binding. Such phrasing does not exclude expression type-signatures. I presume that in the following code, binding b1 does not depend on b2: (x, y) = (z, 1) -- call this binding b1 (z, _) = (2, y) -- call this binding b2 w = 1 + (z :: Double) So my reading was that they meant has no type signature *in b1*. I take it that your reading is that they meant: b1 contains a free identifier that is bound by b2 and b2 is accompanied by a type signature for that identifier I think, given the ambiguities here, it's worth filing a ticket on the haskell' web site. Thank you. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is a simple pattern binding?
Still, the clause b1 contains a free identifier that has no type signature and is bound by b2 applies the phrase has no type signature to the identifier, not to the binding. Such phrasing does not exclude expression type-signatures. True. That ambiguity could be avoided by adding the word declaration after type signature. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is a simple pattern binding?
Still, the clause b1 contains a free identifier that has no type signature and is bound by b2 applies the phrase has no type signature to the identifier, not to the binding. Such phrasing does not exclude expression type-signatures. True. That ambiguity could be avoided by adding the word declaration after type signature. On second thoughts, this is unnecessary. The Report consistently uses expression type signature for the expression and type signature for the declaration. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Enumerator.List.concatMap is to Data.Iteratee.?
Hi: I've been studying iteratee IO. Is there a function in the iteratee package that is analogous to Data.Enumerator.List.concatMap? David Place Owner, Panpipes Ho! LLC http://panpipesho.com d...@vidplace.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is a simple pattern binding?
At Sun, 26 Jun 2011 21:15:06 +0100, Paterson, Ross wrote: True. That ambiguity could be avoided by adding the word declaration after type signature. On second thoughts, this is unnecessary. The Report consistently uses expression type signature for the expression and type signature for the declaration. I already sent the haskell-prime mailing list a proposal for the following wording: A binding b1 depends on a binding b2 in the same list of declarations if either 1. b1 contains a free identifier v, v is bound by b2, and the list of declarations does not contain a type signature for v; or http://www.haskell.org/pipermail/haskell-prime/2011-June/003482.html I think this is clearer, but it might make more sense to discuss on haskell-prime. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alex Lexer Performance Issues
On 26/06/2011, at 10:19 PM, Malcolm Wallace wrote: There is an old folklore that lexing is usually the most expensive phase of any compiler-like traversal. 50% of time and space expended on lexing was pretty common twenty years ago. Indeed it is old, but no, it isn't folklore, you'll find actual measurements in Per Brinch Hansen, and no, what was pretty common twenty years ago is not necessarily valid today. Depending on what you are compiling into what, you could be spending a lot of time reading, a lot of time writing, or a lot of time doing semantic analysis and optimisation. For example, lexing C++ is clearly a linear time operation, but type checking C++ is Turing complete (any computable function can be expressed as a C++ type checking problem). There's a Scheme compiler I know of where semantic analysis is at least O(N**3), N being the number of nodes in the AST. Also, much depends on the level at which you are doing I/O. Stuff layered on top of C stdio can be amazingly slow (thanks in part to libraries that acquire and release a lock for every call to getc() or putc()). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] View Thunk Evaluation
Hi All, Is there a way to determine whether a thunk was evaluated during code's execution? Thanks, Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] View Thunk Evaluation
Yes, via the -hpc tracing mechanism. When executed HPC generates a highlighted log of your source, and expressions that aren't evaluated will be marked up in a special color. On Sun, Jun 26, 2011 at 9:22 PM, Tom Murphy amin...@gmail.com wrote: Hi All, Is there a way to determine whether a thunk was evaluated during code's execution? Thanks, Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Trouble with `foldl` in composition chain.
When profiling this code: consolidateRPR :: [Sample] - [Sample] smplUnionRecursRev :: [Sample] - Sample - [Sample] sortSamps :: [Sample] - [Sample] smplSetUnion :: [Sample] - [Sample] smplSetUnion = consolidateRPR . (foldl smplUnionRecursRev []) . sortSamps I'm getting this: smplSetUnion Data.RandProc 1038 32794 0.70.276.9 72.6 consolidateRPRData.RandProc 1041 32794 0.00.0 8.2 11.8 smplUnionRecursRev Data.RandProc 1040 918112 8.85.6 8.85.6 sortSamps Data.RandProc 1039 1081514 21.1 55.059.2 55.0 I'm confused as to why `sortSamps` is being called so many times. I would expect it to be called 32794 times, just like `consolidateRPR`. It's as if having a `foldl` to the left of `sortSamps` in the composition chain is causing it to execute more than once, per call of `smplSetUnion`, but I wouldn't expect that. This doesn't change anything: smplSetUnion = consolidateRPR . (\ss - foldl smplUnionRecursRev [] ss) . sortSamps (I thought it might explicitly close the `foldl`.) In fact, even this: smplSetUnion ss = consolidateRPR $ foldl smplUnionRecursRev [] ss' where ss' = sortSamps ss doesn't change anything. `sortSamps` still gets entered 1081514 times! Can anyone help clear up this newbie's fog? Thanks, in advance! -db ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
