Re: [Haskell-cafe] parsec: parserFail multiple error messages
The error message can be improved in your examples by using count 5 instead of many1. C. Am 08.08.2012 21:24, schrieb silly: I am trying to create a parsec parser that parses an integer and then checks if that integer has the right size. If not, it generates an error. I tried the following: 8--- import Text.Parsec import Text.Parsec.String integer :: Parser Int integer = do s - many1 digit let n = read s if n 65535 then parserFail integer overflow else return n 8--- The problem is that when I try this parse integer 7 I get the following error: Left (line 1, column 6): unexpected end of input expecting digit integer overflow ie there are three error messages but I only want the last one. Is there something I can do about this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mutable arrays of tuples
David Feuer david.fe...@gmail.com writes: So I was thinking about a mutable array of tuples, but to avoid allocating tuples to modify their fields, I guess I really want an immutable array of tuples of STRefs. Just how much less efficient is this than a plain mutable array? might it even make sense to use parallel mutable arrays? The thought of that is disgusting to me, but at least one of the arrays could likely be made unboxed... Maybe you could use a tuple of (unboxed) arrays instead? Or if you use Vector instead of Array, I think tuples are member of Unbox (as long as the tuple elements are), and can be used directly in unboxed vectors. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fwd: 'let' keyword optional in do notation?
Hi, Martijn Schrage wrote: Would expanding each let-less binding to a separate let feel more sound to you? That was actually my first idea, but then two declarations at the same level will not be in the same binding group, so do x = y y = 1 would not compile. This would create a difference with all the other places where bindings may appear. But it would be in line with - bindings in the do notation, so maybe it wouldn't feel so wrong. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Data and OverlappingInstances
Hi cafe,
in my code I use Data.Data and OverlappingInstances. My problem now is,
that I can't use functions using these instances as arguments for
fromConstrM.
This is what my problem looks like:
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverlappingInstances #-}
{-# LANGUAGE UndecidableInstances #-}
import Data.Data
class Test a where
foo :: Monad m = m a
instance Num a = Test a where
foo = return 1
instance Test Int where
foo = return 2
test constr = fromConstrM foo constr
but when I compile I get:
test.hs:15:26:
Overlapping instances for Test d
arising from a use of `foo' at test.hs:15:26-28
Matching instances:
instance [overlap ok] (Num a) = Test a
-- Defined at test.hs:9:9-23
instance [overlap ok] Test Int -- Defined at test.hs:12:9-16
(The choice depends on the instantiation of `d'
To pick the first instance above, use -XIncoherentInstances
when compiling the other instance declarations)
In the first argument of `fromConstrM', namely `foo'
In the expression: fromConstrM foo constr
In the definition of `test': test constr = fromConstrM foo constr
Failed, modules loaded: none.
Is there a way out? Right now I use a case (typeOf x) of kind of
construct, but it gets pretty messy and I even have to unsafeCoerce at one
point.
- Timo
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Re: [Haskell-cafe] 3 level hierarchy of Haskell objects
On 09/08/12, Jay Sulzberger j...@panix.com wrote:Here we are close to the distinction between a class of objectswhich satisfy a condition vs objects with added structure, forwhich see: http://math.ucr.edu/home/baez/qg-spring2004/discussion.html http://ncatlab.org/nlab/show/stuff,+structure,+propertyoo--JS.This seems to be addressing my my question, but I am not sure that I can relate the above ideas to Haskell.Below is my current (naive) understanding and some further question:objects which satisfy a condition Could these objects be models that have the same signature (instances in Haskell). Haskell type classes seem to be signature only (no equations, ignoring default methods) so in general they provide an empty theory with no logical consequences.objects with added structureI am struggling with this concept both in general and in relation to the hierarchy from my earlier posting.Could this be model expansion where a theory describing an existing model is enriched with additional axioms.The enriched theory is then satisfied by models with more structure (operations).I am unsure about the size of this expanded model and the number of potential expanded models. Would a expanded model have less elements?Would there be fewer models for the enriched theory?In relation to Haskell data types also have structure (constructors). The data types can be used to build other data types (is this model expansion?)I am not sure if the model (instance) of a sub-class could be considered as expanded model of its super-class.Your reply was very helpfulThanks,Pat Tá an teachtaireacht seo scanta ó thaobh ábhar agus víreas ag Seirbhís Scanta Ríomhphost de chuid Seirbhísí Faisnéise, ITBÁC agus meastar í a bheith slán. http://www.dit.ie This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mutable arrays of tuples
In fact, unboxed arrays of tuples are represented in vector as tuples of unboxed arrays. On Aug 9, 2012 4:35 AM, Ketil Malde ke...@malde.org wrote: David Feuer david.fe...@gmail.com writes: So I was thinking about a mutable array of tuples, but to avoid allocating tuples to modify their fields, I guess I really want an immutable array of tuples of STRefs. Just how much less efficient is this than a plain mutable array? might it even make sense to use parallel mutable arrays? The thought of that is disgusting to me, but at least one of the arrays could likely be made unboxed... Maybe you could use a tuple of (unboxed) arrays instead? Or if you use Vector instead of Array, I think tuples are member of Unbox (as long as the tuple elements are), and can be used directly in unboxed vectors. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ 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
Re: [Haskell-cafe] 3 level hierarchy of Haskell objects
Hi, Patrick Browne wrote: Haskell type classes seem to be signature only (no equations, ignoring default methods) so in general they provide an empty theory with no logical consequences. Note that many type classes in Haskell have equations annotated as comments. For example, the monad laws are mentioned in the documentation of the Monad type class: http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#t:Monad In this context, see also the current thread about what equations we can expect to hold for Eq instances: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/99517 Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] 3 level hierarchy of Haskell objects
Hello, On Thu, Aug 9, 2012 at 1:52 PM, Tillmann Rendel ren...@informatik.uni-marburg.de wrote: Note that many type classes in Haskell have equations annotated as comments. For example, the monad laws are mentioned in the documentation of the Monad type class: One of the reasons why I chose Haskell over Scheme about 4 years ago was that in the PLT Scheme (now Racket) libraries, type annotation were given in the comments. I thought: maybe those things are in fact useful. Perhaps in Haskell we could have a lightweight Quasi-quoting/Template Haskell library for adding laws to class definitions? Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Data and OverlappingInstances
On Thu, Aug 9, 2012 at 6:00 AM, Timo von Holtz timo.v.ho...@gmail.comwrote: instance Num a = Test a where foo = return 1 instance Test Int where foo = return 2 Erm, this isn't going to work anyway, is it? I think the first instance matches all types and then throws an error if the result isn't an instance of Num? -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] parsec: parserFail multiple error messages
On Thu, Aug 9, 2012 at 3:59 AM, Christian Maeder christian.mae...@dfki.de wrote: The error message can be improved in your examples by using count 5 instead of many1. Yes, I know. That's what I ended up doing. But this is an ad hoc solution. I think parsec should offer a more general solution. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Possible bug in Criterion or Statistics package
On 07.08.2012 19:15, Aleksey Khudyakov wrote: On 07.08.2012 18:16, Till Berger wrote: Dear all, So I am not sure if this is a bug in Criterion itself, the Statistics package or any dependency or if I am doing something obviously wrong. I would be grateful if someone could look into this as it is holding me back from using Criterion for benchmarking my code. I would suspect Statistics.Resampling.resample. From quick glance criterion doesn't use any concurrent stuff. I'll try create smaller test case It looks like I'm wrong. I obtained event log from crashing program and resample completed its work without problems. Crash occured later. Next suspect is bootstrapBCA itself. It uses monad-par to obtain parallelism[1]. I tried to create smaller test case without any success. [1] https://github.com/bos/statistics/blob/master/Statistics/Resampling/Bootstrap.hs#L84 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parsec type error with Flexible Contexts
Hi. I wanted to generalize the definitions in Text.Parsec.Language to be able to use them with Parsec Text instead of Parsec String. I'm getting a type error with the following code snippet: http://hpaste.org/72844 I don't really understand the error, specially with regard to the fact that the if I comment one of the marked lines on the code pasted the program build. Any help is welcome. Greetings. -- marcot http://marcot.eti.br/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] 3 level hierarchy of Haskell objects
On 8/8/12 9:41 PM, Jay Sulzberger wrote: Haskell's type classes look to me to be a provision for declaring a signature in the sense of the above article. Just to clarify this in the context of my previous post, type classes define signatures in two significantly different ways. (1) The first way is as you suggest: the methods of a type class specify a signature, and for convenience we give that signature a name (i.e., the type class' name). However, this is a signature for the term level of Haskell (i.e., a signature in the Term sort not discussed previously; elements of Type classify elements of Term, just as elements of Kind classify elements of Type). (2) The second way is that, at the type level, the collection of type class names together form a signature. Namely they form the signature comprising the majority of the Context sort. Both senses are important for understanding the role of type classes in Haskell, but I believe that some of Patrick Browne's confusion is due to trying to conflate these into a single notion. Just as terms and types should not be confused, neither should methods and type classes. In both cases, each is defined in terms of the other, however they live in separate universes. This is true even in languages which allow terms to occur in type expressions and allow types to occur in term expressions. Terms denote values and computations (even if abstractly); whereas, types denote collections of expressions (proper types denote collections of term expressions; kinds denote collections of type expressions;...). -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parsec type error with Flexible Contexts
Hello!
I've managed to reduce your code to a much simpler test case (without
parsec) but I'm still not sure why this is happening:
{-# LANGUAGE MultiParamTypeClasses, FlexibleContexts #-}
data D m
= D { bar1 :: P m ()
, bar2 :: P m ()
}
data P m c = P
class S m c where
foo :: S m () = P m ()
foo = undefined
emptyDef :: S m () = D m
emptyDef
= D
{ bar1 = foo
, bar2 = foo
}
haskellStyle :: S m () = D m
haskellStyle
= emptyDef
{ bar1 = foo
, bar2 = foo
}
Cheers,
--
Felipe.
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Re: [Haskell-cafe] Parsec type error with Flexible Contexts
Here's an even smaller one:
{-# LANGUAGE MultiParamTypeClasses, FlexibleContexts #-}
data D m = D { bar :: P m () }
data P m c = P
class S m c where
foo :: S m () = P m ()
foo = undefined
emptyDef :: S m () = D m
emptyDef = D foo
haskellStyle :: S m () = D m
haskellStyle = emptyDef { bar = foo }
Cheers,
--
Felipe.
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Re: [Haskell-cafe] parsec: parserFail multiple error messages
On 12-08-08 03:24 PM, silly wrote: The problem is that when I try this parse integer 7 I get the following error: Left (line 1, column 6): unexpected end of input expecting digit integer overflow ie there are three error messages but I only want the last one. Is there something I can do about this? import Text.Parsec import Text.Parsec.String integer :: Parser Int integer = try integ3r ? number at most 65535 integ3r = do s - many1 digit let n = read s if n 65535 then unexpected number overflow else return n main = do parseTest integer a7 parseTest integer 7 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [Wadler 89] Philip Wadler. Theorems for free!: Can't get the same results in Haskell
Hi there, I was reading Real World Haskell and found this paper. [1] On the first page of the paper there is an example: inc* (odds_Int [1,2,3]) = [2,4] /= [4] = odds_Int (inc* [1,2,3]) I tried to implement it in Haskell: (I'm a newbie. I guess it's possible to write a better version.) module Param where import Prelude odds :: [Int] - [Int] odds [] = [] odds [x] = if odd x then [x] else [] odds (x:xs) = if odds [x] == [] then odds xs else [x] ++ odds xs inc :: [Int] - [Int] inc [] = error Empty list inc [x] = [succ x] inc (x:xs) = inc [x] ++ inc xs Looks fine: *Param odds [1,2,3] [1,3] *Param inc [1,2,3] [2,3,4] But my results differ from the paper's: *Param inc (odds [1,2,3]) [2,4] *Param odds (inc [1,2,3]) [3] I doubt that there is an error in the paper. So it seems that something is wrong with my code. But I can't find the error. Could you help me? (Or there is no error at all and I misunderstood something.) [1] http://ttic.uchicago.edu/~dreyer/course/papers/wadler.pdf Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Wadler 89] Philip Wadler. Theorems for free!: Can't get the same results in Haskell
It looks to me like Wadler made a typo. Even great minds like his slip up like that sometimes. However, I do have some comments below on your code. On Aug 9, 2012 8:53 PM, Stayvoid stayv...@gmail.com wrote: I tried to implement it in Haskell: (I'm a newbie. I guess it's possible to write a better version.) module Param where import Prelude The prelude is imported automatically. You only need to mention it as an import if you need to *avoid* importing some functions, or want some functions to be imported only qualified. This is done if you want to use a name that clashes with one in the prelude. You'll see things like import Prelude hiding (foldl',foldl, foldr) import Prelude qualified as P in a module implementing a data structure that supports folds. odds :: [Int] - [Int] odds [] = [] This is a very awkward approach. There's no reason to have a special case for the one-element list, and certainly no reason to use ++ to add a single element to the front of a list. You should do the work in the (x:xs) case instead: odds [] = [] odds (x:xs) | odd x = x : odds xs | otherwise = odds xs In fact, there's a function called filter that captures this pattern, so you can even write: odds = filter odd odds [x] = if odd x then [x] else [] odds (x:xs) = if odds [x] == [] then odds xs else [x] ++ odds xs inc :: [Int] - [Int] inc [] = error Empty list inc [x] = [succ x] inc (x:xs) = inc [x] ++ inc xs Again, this is bizarre. You should be writing: inc [] = [] inc (x:xs) = succ x : inc xs Again, there is a function that captures this pattern, so you can shorten it to inc = map succ Looks fine: *Param odds [1,2,3] [1,3] *Param inc [1,2,3] [2,3,4] But my results differ from the paper's: *Param inc (odds [1,2,3]) [2,4] *Param odds (inc [1,2,3]) [3] I doubt that there is an error in the paper. I don't. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] MIN_VERSION_base
Hello, The stable branch of the network library includes the following code: #if !(MIN_VERSION_base(4,6,0)) I cannot compile the stable branch with HP 2011.4.0.0 on Linux 2: Preprocessing library network-2.3.0.14... BSD.hsc:115:23: error: missing binary operator before token ( BSD.hsc:115:23: error: missing binary operator before token ( BSD.hsc:115:23: error: missing binary operator before token ( compiling dist/build/Network/BSDhsc_make.c failed (exit code 1) command was: /usr/bin/gcc -c dist/build/Network/BSD_hsc_make.c -o dist/build/Network/BSD_hsc_make.o -fno-stack-protector -fno-stack-protector -DGLASGOW_HASKELL_=700 -Dlinux_BUILD_OS -Dlinux_HOST_OS -Di386_BUILD_ARCH -Di386_HOST_ARCH -Iinclude -DCALLCONV=ccall -I/ghc7.0.4/lib/ghc-7.0.4/unix-2.4.2.0/include -I/ghc7.0.4/lib/ghc-7.0.4/bytestring-0.9.1.10/include -I/ghc7.0.4/lib/ghc-7.0.4/base-4.3.1.0/include -I/ghc7.0.4/lib/ghc-7.0.4/include -I/ghc7.0.4/lib/ghc-7.0.4/include -I/ghc7.0.4/lib/ghc-7.0.4/include/ dist/build/autogen/cabal_macros.h defines MIN_VERSION_base but dist/build/Network/BSD_hsc_make.c does not include it. If you guys know why this happens, please let me know. For more information, please refer to: https://github.com/haskell/network/issues/43 --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MIN_VERSION_base
On Thu, Aug 9, 2012 at 8:50 PM, Kazu Yamamoto k...@iij.ad.jp wrote: Hello, The stable branch of the network library includes the following code: #if !(MIN_VERSION_base(4,6,0)) I cannot compile the stable branch with HP 2011.4.0.0 on Linux 2: Preprocessing library network-2.3.0.14... BSD.hsc:115:23: error: missing binary operator before token ( BSD.hsc:115:23: error: missing binary operator before token ( BSD.hsc:115:23: error: missing binary operator before token ( compiling dist/build/Network/BSDhsc_make.c failed (exit code 1) command was: /usr/bin/gcc -c dist/build/Network/BSD_hsc_make.c -o dist/build/Network/BSD_hsc_make.o -fno-stack-protector -fno-stack-protector -DGLASGOW_HASKELL_=700 -Dlinux_BUILD_OS -Dlinux_HOST_OS -Di386_BUILD_ARCH -Di386_HOST_ARCH -Iinclude -DCALLCONV=ccall -I/ghc7.0.4/lib/ghc-7.0.4/unix-2.4.2.0/include -I/ghc7.0.4/lib/ghc-7.0.4/bytestring-0.9.1.10/include -I/ghc7.0.4/lib/ghc-7.0.4/base-4.3.1.0/include -I/ghc7.0.4/lib/ghc-7.0.4/include -I/ghc7.0.4/lib/ghc-7.0.4/include -I/ghc7.0.4/lib/ghc-7.0.4/include/ dist/build/autogen/cabal_macros.h defines MIN_VERSION_base but dist/build/Network/BSD_hsc_make.c does not include it. If you guys know why this happens, please let me know. For more information, please refer to: https://github.com/haskell/network/issues/43 I should note that it compiles on GHC 7.0.3 and a bunch of other versions: http://ci.johantibell.com/job/network/ I suspect that it's either a GHC problem (not passing the right arguments to hsc2hs) or a cabal problem. -- Johan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
