Re: [Haskell-cafe] An experimental Zipper using Thrists and first-class Labels. Help or thoughts?
On Mon, Jul 26, 2010 at 10:59 PM, Jason Dagit da...@codersbase.com wrote: ($) is application, but in the space of functions it is identity. So, if you think the elements in your thrist as being values in the space of functions, you're asking for a right fold that is like, v1 `id` (v2 `id` (v3 `id` ...), which I hope you agree doesn't make that much sense. I just realized a better way to phrase this analogy is that id and ($) are 0, and (.) is (+). So your foldr expands like: v1 `0` (v2 `0` (v3 `0` (vn `0` 0) ... ) But if you use (.), it expands like: v1 + (v2 + (v3 + ... (vn + 0) ... ) I guess you could pick id = ($) = 1, and (.) = (*). I think the analogy works equally well, but I might be forgetting something simple. Either way, I bet you get what I'm rambling about so I'll stop now :) Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: weighted-regexp-0.1.0.0
On Jul 27, 2010, at 7:09 AM, Sebastian Fischer wrote: I find eachOnce :: [RegExp c] - RegExp c eachOnce = foldr alt noMatch . map (foldr seq_ eps) . permutations even clearer but your version is *much* better as it uses nesting to combine all alternatives that start with the same regexp. Yes, this was what I had at first too, but trying to match this on 8 items takes 2 seconds and 9 items already takes one minute. -- Sjoerd Visscher http://w3future.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: weighted-regexp-0.1.0.0
On Jul 27, 2010, at 7:09 AM, Sebastian Fischer wrote: I'll add noMatch :: RegExp c noMatch = psym [] (const False) Oh, by the way, with noMatch, eps, alt and seq_ RegExp is itself a Semiring, but I'm not sure what that would do. -- Sjoerd Visscher http://w3future.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: weighted-regexp-0.1.0.0
Perhaps this might mean that we can get incremental and parallel regexp matching by associating each character with a linear operator (matrix) over this or related semiring, or something, and mixing that with two sigfpe's articles: http://blog.sigfpe.com/2008/11/approach-to-algorithm-parallelisation.html http://blog.sigfpe.com/2009/01/fast-incremental-regular-expression.html 2010/7/27 Sjoerd Visscher sjo...@w3future.com: On Jul 27, 2010, at 7:09 AM, Sebastian Fischer wrote: I'll add noMatch :: RegExp c noMatch = psym [] (const False) Oh, by the way, with noMatch, eps, alt and seq_ RegExp is itself a Semiring, but I'm not sure what that would do. -- Sjoerd Visscher http://w3future.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoids and monads
John Lato schrieb: Hello, I was wondering today, is this generally true? instance (Monad m, Monoid a) = Monoid (m a) where mempty = return mempty mappend = liftM2 mappend I know it isn't a good idea to use this instance, but assuming that the instance head does what I mean, is it valid? Or more generally is it true for applicative functors as well? I think it works for a few tricky monads, but that's not any sort of proof. I don't even know how to express what would need to be proven here. I translate 'valid' and 'true' to Is 'm a' a Monoid, given that 'm' is a Monad and 'a' is a Monoid? If this is the question then we have to show the Monoid laws for (m a), namely left identity: forall x. mappend mempty x = x right identity: forall x. mappend x mempty = x associativity: forall x y z. (x `mappend` y) `mappend` z = x `mappend` (y `mappend` z) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: weighted-regexp-0.1.1.0
I have released weighted-regexp-0.1.1.0 with two additional combinators: -- | Does not match anything. 'noMatch' is an identity for 'alt'. -- noMatch :: RegExp c -- | -- Matches a sequence of the given regular expressions in any -- order. For example, the regular expression -- -- @ -- perm (map char \abc\) -- @ -- -- has the same meaning as -- -- @ -- abc|acb|bcc|bac|cba|cab -- @ -- -- and is represented as -- -- @ -- a(bc|cb)|b(ca|ac)|c(ba|ab) -- @ -- perm :: [RegExp c] - RegExp c Cheers, Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is 'flip' really necessary?
(??) is misleading, some may be tempted to write things like: func ?? 45 ?? x , forgetting that ?? is just a mere operator, not a syntactic convenience. Unfortunately, Haskell doesn't provide Scala's underscore for partially applied functions: func(56, _, foo, _) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: weighted-regexp-0.1.0.0
On Jul 27, 2010, at 9:15 AM, Sjoerd Visscher wrote: Oh, by the way, with noMatch, eps, alt and seq_ RegExp is itself a Semiring, Yes, but it's hard to define an Eq instance for arbitrary regular expressions that reflects equivalence of regexps. There is currently only `instance Eq (RegExp Char)` which implements structural identity used for the QuickCheck tests. but I'm not sure what that would do. I think matching a regular expression against a word in the regular expressions semiring returns an unfolding of the original regular expression which matches exactly the given word. Sebastian -- Underestimating the novelty of the future is a time-honored tradition. (D.G.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Announce snm-0.0.2: Oops
Sorry if I have left typos, it's very late I knew it was a bit late to be uploading things, I forgot to say where anyone interested might download this: it's on Hackage so just cabal install snm Cheers Johnny ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Instances for Set of Functor, Traversable?
Lennart Augustsson wrote:
Try to make Set an instance of Functor and you'll see why it isn't.
It's very annoying.
And yet the very simple, and old solution works.
http://okmij.org/ftp/Haskell/types.html#restricted-datatypes
We just properly generalize Functor, so that all old functors are new
functors. In addition, many more functors become possible, including
Set. In general, we can have functors
fmap' :: (C1 a, C2 b) = (a - b) - f a - f b
Incidentally, even an Integer may be considered a functor:
we can define the fmap' operation fitting the above signature, where
the constraint C1 a is a ~ Integer.
Although the use of OverlappingInstances is not required, the
extension leads to the nicest code; all old functors just work.
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
{-# LANGUAGE OverlappingInstances #-}
module FunctorEx where
import Control.Monad
import Data.Set as S
class Functor' f a b where
fmap' :: (a - b) - f a - f b
-- The default instance:
-- All ordinary Functors are also extended functors
instance Functor f = Functor' f a b where
fmap' = fmap
-- Now define a functor for a set
instance (Ord a, Ord b) = Functor' S.Set a b where
fmap' = S.map
-- Define a degenerate functor, for an integer
newtype I a = I Integer deriving Show
instance Functor' I Integer Integer where
fmap' f (I x) = I $ f x
-- tests
-- Lists as functors
test_l = fmap' (+10) [1,2,3,4]
-- [11,12,13,14]
-- Sets as functors
test_s = fmap' (\x - x `mod` 3) $ S.fromList [1,2,3,4]
-- fromList [0,1,2]
-- Integer as functor
test_i = fmap' (* (6::Integer)) $ I 7
-- I 42
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Re: [Haskell-cafe] Re: Instances for Set of Functor, Traversable?
But that's not really a solution, since it doesn't make a Functor
instance for Set; it makes a Functor' instance for Set.
If you are willing to not be upwards compatible then, yes, there are solutions.
I think the best bet for an upwards compatible solutions is the
associated constraints,
www.cs.kuleuven.be/~toms/Research/papers/constraint_families.pdf
On Tue, Jul 27, 2010 at 10:17 AM, o...@okmij.org wrote:
Lennart Augustsson wrote:
Try to make Set an instance of Functor and you'll see why it isn't.
It's very annoying.
And yet the very simple, and old solution works.
http://okmij.org/ftp/Haskell/types.html#restricted-datatypes
We just properly generalize Functor, so that all old functors are new
functors. In addition, many more functors become possible, including
Set. In general, we can have functors
fmap' :: (C1 a, C2 b) = (a - b) - f a - f b
Incidentally, even an Integer may be considered a functor:
we can define the fmap' operation fitting the above signature, where
the constraint C1 a is a ~ Integer.
Although the use of OverlappingInstances is not required, the
extension leads to the nicest code; all old functors just work.
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
{-# LANGUAGE OverlappingInstances #-}
module FunctorEx where
import Control.Monad
import Data.Set as S
class Functor' f a b where
fmap' :: (a - b) - f a - f b
-- The default instance:
-- All ordinary Functors are also extended functors
instance Functor f = Functor' f a b where
fmap' = fmap
-- Now define a functor for a set
instance (Ord a, Ord b) = Functor' S.Set a b where
fmap' = S.map
-- Define a degenerate functor, for an integer
newtype I a = I Integer deriving Show
instance Functor' I Integer Integer where
fmap' f (I x) = I $ f x
-- tests
-- Lists as functors
test_l = fmap' (+10) [1,2,3,4]
-- [11,12,13,14]
-- Sets as functors
test_s = fmap' (\x - x `mod` 3) $ S.fromList [1,2,3,4]
-- fromList [0,1,2]
-- Integer as functor
test_i = fmap' (* (6::Integer)) $ I 7
-- I 42
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Re: [Haskell-cafe] monoids and monads
On Tue, Jul 27, 2010 at 8:32 AM, Henning Thielemann schlepp...@henning-thielemann.de wrote: John Lato schrieb: Hello, I was wondering today, is this generally true? instance (Monad m, Monoid a) = Monoid (m a) where mempty = return mempty mappend = liftM2 mappend I know it isn't a good idea to use this instance, but assuming that the instance head does what I mean, is it valid? Or more generally is it true for applicative functors as well? I think it works for a few tricky monads, but that's not any sort of proof. I don't even know how to express what would need to be proven here. I translate 'valid' and 'true' to Is 'm a' a Monoid, given that 'm' is a Monad and 'a' is a Monoid? If this is the question then we have to show the Monoid laws for (m a), namely Thanks very much, this is what I was unable to express properly (hence the informal description). left identity: forall x. mappend mempty x = x right identity: forall x. mappend x mempty = x associativity: forall x y z. (x `mappend` y) `mappend` z = x `mappend` (y `mappend` z) So the task now is to prove that these laws hold, given the instance I defined above, the monoid laws for 'a', and the monad laws for 'm'. Or alternatively using applicative laws for 'm' for the more general case. I'll see how I get on from here then. Thanks, John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoids and monads
On Mon, Jul 26, 2010 at 5:02 PM, Edward Kmett ekm...@gmail.com wrote: On Mon, Jul 26, 2010 at 11:55 AM, John Lato jwl...@gmail.com wrote: Hello, I was wondering today, is this generally true? instance (Monad m, Monoid a) = Monoid (m a) where mempty = return mempty mappend = liftM2 mappend There are multiple potential monoids that you may be interested in here. There is the monoid formed by MonadPlus, there is the monoid formed by wrapping a monad (or applicative) around a monoid, which usually forms part of a right seminearring because of the left-distributive law, there are also potentially other monoids for particular monads. See the monad module in my monoids package: http://hackage.haskell.org/packages/archive/monoids/0.2.0.2/doc/html/Data-Monoid-Monad.html I think your monoids package has grown since I last looked at it. I'll take a look. Any resources for how I could develop a means to reason about this sort of property? The types are not enough. What you need is the associativity of Kleisli arrow composition and the two identity laws. The three monad laws are precisely what you need to form this monoid. There are analogous laws for Applicative that serve the same purpose. Thanks very much. With this and Henning's hints, I think I can make some progress with this now. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Forum
Brandon S Allbery KF8NH allb...@ece.cmu.edu writes: Usenet *is* NNTP. In the same way the web is HTTP... (Usenet is a set of global, distributed forums using a message format similar enough to email (RFC822 + extensions) that many mail reader software supports news, and vice versa. NNTP is the protocol used for user access and distribution. IIRC - anybody interested in more accuracy will have to look it up :-) -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] Re: Instances for Set of Functor, Traversable?
o...@okmij.org writes: class Functor' f a b where fmap' :: (a - b) - f a - f b I was about to ask why you mentioned b in the type signature as well, as I thought just having (Functor' f b) as a constraint in the type signature of fmap' would be sufficient, but when I went to check I found that I was mistaken. *sigh* this is going to make some of my code even uglier than it already is :( -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] 1st attempt at concurrency
Dear Jason, And yes, Orc is pretty cool and should be perfectly suited for what you're doing as fetching data from websites was one of the original use cases for Orc. Jason thanks for that, it's nice to be on the right track for once. Günther ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Actors and message-passing a la Erlang
Hi Yves, You say that With the help of this library it is possible to build Erlang-Style mailboxes, but how would you solve the issue of static typing? this wasn't an issue for me because I wanted as much type checking as possible. In many implementations, you have an implicit contract between the sender and the receiver process. In this case, the contract is explicit and the compiler can tell me if I'm trying to send or receive wrong data. Besides, Holumbus depends on package 'unix', preventing it from being used on non-unix platforms. Oh... hmm, I think, the unix-package is only needed for the console-modules. The distribution modules should not need them, but I may be wrong. I don't have access to proprietary plattforms, but I think about splitting the distribution package and extract the communication modules. Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Forum
On Tue, Jul 27, 2010 at 12:09 AM, aditya siram aditya.si...@gmail.com wrote: We have a Google group. Doesn't that qualify? One can't post to Haskell Cafe through the usenet/NNTP/google group interface... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoids and monads
John Lato schrieb: Hello, I was wondering today, is this generally true? instance (Monad m, Monoid a) = Monoid (m a) where mempty = return mempty mappend = liftM2 mappend I know it isn't a good idea to use this instance, but assuming that the instance head does what I mean, is it valid? Or more generally is it true for applicative functors as well? I think it works for a few tricky monads, but that's not any sort of proof. I don't even know how to express what would need to be proven here. I always assumed that 'm a' would be a monoid for 'm' being an applicative functor, but I never tried to prove it. Now you made me performing a proof. However the applicative functor laws from http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control-Applicative.html are quite unintuitive and the proofs are certainly not very illustrative. For the proof of the associativy I have just started from both ends and worked toward where the associativity of 'a' has to be inserted, added some mistakes and restarted. Left Identity - (mappend mempty x :: m a) = liftA2 mappend (pure mempty) x = pure mappend * pure mempty * x = pure (mappend mempty) * x = pure id * x = x Right Identity -- (mappend x mempty :: m a) = liftA2 mappend x (pure mempty) = (pure mappend * x) * pure mempty = pure ($mempty) * (pure mappend * x) = pure (.) * pure ($mempty) * pure mappend * x = pure ((.) ($mempty)) * pure mappend * x = pure (($mempty).) * pure mappend * x = pure ((($mempty).) mappend) * x = pure (($mempty) . mappend) * x = pure (\a - ($mempty) (mappend a)) * x = pure (\a - (mappend a) mempty) * x = pure (\a - a) * x = pure id * x = x For monads I find the proof more intuitive: liftM2 mappend x (pure mempty) = do y - x z - pure mempty return (mappend y z) = do y - x return (mappend y mempty) = do y - x return y = x Associativity - ((x `mappend` y) `mappend` z) :: m a = (pure mappend * x * y) `mappend` z = pure mappend * (pure mappend * x * y) * z = pure (.) * pure mappend * (pure mappend * x) * y * z = pure (mappend.) * (pure mappend * x) * y * z = pure (.) * pure (mappend.) * pure mappend * x * y * z = pure ((mappend.).) * pure mappend * x * y * z = pure ((mappend.) . mappend) * x * y * z -- see proof below = pure (($mappend).((.).((.).mappend))) * x * y * z = pure (.) * pure ($mappend) * pure ((.).((.).mappend)) * x * y * z = pure ($mappend) * (pure ((.).((.).mappend)) * x) * y * z = pure ((.).((.).mappend)) * x * pure mappend * y * z = pure (.) * pure (.) * pure ((.).mappend) * x * pure mappend * y * z = pure (.) * (pure ((.).mappend) * x) * pure mappend * y * z = pure ((.).mappend) * x * (pure mappend * y) * z = pure (.) * pure (.) * pure mappend * x * (pure mappend * y) * z = pure (.) * (pure mappend * x) * (pure mappend * y) * z = (pure mappend * x) * ((pure mappend * y) * z) = pure mappend * x * (pure mappend * y * z) = x `mappend` (pure mappend * y * z) = x `mappend` (y `mappend` z) ((mappend.) . mappend) x y z = (mappend.) (mappend x) y z = (\f - mappend.f) (mappend x) y z = (\f x - mappend (f x)) (mappend x) y z = mappend (mappend x y) z -- Monoid associativity for type 'a' = mappend x (mappend y z) = (.) (mappend x) (mappend y) z = ((.).mappend) x (mappend y) z = (.) (((.).mappend) x) mappend y z = ((.).((.).mappend)) x mappend y z = ($mappend) (((.).((.).mappend)) x) y z = (($mappend).((.).((.).mappend))) x y z ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Actors and message-passing a la Erlang
On Tue, Jul 27, 2010 at 5:27 AM, Stefan Schmidt stefanschmid...@googlemail.com wrote: Hi Yves, You say that With the help of this library it is possible to build Erlang-Style mailboxes, but how would you solve the issue of static typing? this wasn't an issue for me because I wanted as much type checking as possible. In many implementations, you have an implicit contract between the sender and the receiver process. In this case, the contract is explicit and the compiler can tell me if I'm trying to send or receive wrong data. I've found that I like Erlang's pattern matching for sorting through different kinds of data payloads, but that I prefer to use typed data channels per Limbo, Go, Plan 9's thread and messaging libraries etc. I've often wanted an Erlang with static typing to get this capability. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Actors and message-passing a la Erlang
This may not be of direct interest to the Haskell community but I thought I'd share this information anyway. If you are looking for a solution (in Erlang that runs on Erlang's virtual machine) to enforce an explicit contract between a client and a server, there is framework called UBF. This framework is designed for providing rpc-like services based on a contract. The contract is enforced dynamically at runtime (not at compile time). The original implementation was made by Joe Armstrong (http://www.sics.se/~joe/ubf/site/home.html). An updated implementation with new features is currently hosted on GitHub (www.github.com/norton). thanks, - Joe N. On Tue, 27 Jul 2010 22:13:07 +0900, David Leimbach leim...@gmail.com wrote: On Tue, Jul 27, 2010 at 5:27 AM, Stefan Schmidt stefanschmid...@googlemail.com wrote: Hi Yves, You say that With the help of this library it is possible to build Erlang-Style mailboxes, but how would you solve the issue of static typing? this wasn't an issue for me because I wanted as much type checking as possible. In many implementations, you have an implicit contract between the sender and the receiver process. In this case, the contract is explicit and the compiler can tell me if I'm trying to send or receive wrong data. I've found that I like Erlang's pattern matching for sorting through different kinds of data payloads, but that I prefer to use typed data channels per Limbo, Go, Plan 9's thread and messaging libraries etc. I've often wanted an Erlang with static typing to get this capability. -- nor...@alum.mit.edu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoids and monads
On Tuesday 27 July 2010 8:50:56 am Henning Thielemann wrote: I always assumed that 'm a' would be a monoid for 'm' being an applicative functor, but I never tried to prove it. Now you made me performing a proof. However the applicative functor laws from http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control- Applicative.html are quite unintuitive and the proofs are certainly not very illustrative. Perhaps a clearer approach is to look at the category theory behind this. First, a monoid object in a monoidal category (C, I, ⊗) consists of An object M e : I - M m : M ⊗ M - M satisfying unit and associativity diagrams. Second, a lax monoidal functor F between two monoidal categories C and D gets you: unit : I_D - F I_C pair : FA ⊗_D FB - F(A ⊗_C B) also satisfying unit and associativity diagrams. We're only dealing with endofunctors, so the above simplifies to: unit : I - F I pair : forall A B. F A ⊗ F B - F(A ⊗ B) and in the Haskell case, you get applicative functors via: pure x = fmap (const x) unit f * x = fmap (uncurry ($)) (pair (f, x)) So, if we have a monoid object M and monoidal functor F, then we have: Fe . unit : I - FM Fm . pair : FM ⊗ FM - FM which should be suggestive. From there, the unit and associativity laws for FM as a monoid object should follow pretty naturally using laws of the parts. For instance... I ⊗ FM - FI ⊗ FM - FM ⊗ FM - F(M ⊗ M) - FM is the same as I ⊗ FM - FM via the isomorphism for the monoidal category 1) We know that I ⊗ FM - FI ⊗ FM - F(I ⊗ M) - FM is the same as I ⊗ FM - FM from F's left-identity coherence law 2) We know that I ⊗ M - M ⊗ M - M is the same as I ⊗ M - M from M's left-identity law, and thus F(I ⊗ M) - F(M ⊗ M) - FM is the same as F(I ⊗ M) - FM from F being a functor. 3) Finally, we know that FI ⊗ FM - FM ⊗ FM - F(M ⊗ M) is the same as FI ⊗ FM - F(I ⊗ M) - F(M ⊗ M) because 'pair' is supposed to be natural in A and B. So: I ⊗ FM - FM is the same as (1) I ⊗ FM - FI ⊗ FM - [F(I ⊗ M) - FM] is the same as (2) I ⊗ FM - [FI ⊗ FM - F(I ⊗ M) - F(M ⊗ M)] - FM is the same as (3) I ⊗ FM - FI ⊗ FM - FM ⊗ FM - F(M ⊗ M) - FM which is left-identity. Right-identity is exactly the same proof with objects reflected around the ⊗. Associativity of the monoid should be a similar application of the associativity laws, plus functor and naturality identities. You could also couch these in terms of Haskell if preferred: unit :: f () pair :: (f a, f b) - f (a, b) assoc (x, (y, z)) = ((x, y), z) fmap (f *** g) . pair = pair . (fmap f *** fmap g) fmap assoc . pair . (id *** pair) = pair . (pair *** id) . assoc etc. Alternately, if you accept authority: Lax monoidal functors send monoids to monoids http://ncatlab.org/nlab/show/monoidal+functor -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is 'flip' really necessary?
aditya siram wrote: Eta-reducing is nice, and sometimes it makes code more readable. But 'flip' is one of those functions that always seems to hinder rather than help readability, conversely factoring out flip always makes code easier to comprehend. I don't see a need for its existence - maybe I'm missing something and more experienced Haskellers can comment. Not quite Haskell but, in combinator calculi 'flip' is unexpectedly powerful. It'd be odd not to have/use it in Haskell. Though in general I agree that it should be used sparingly, for legibility's sake. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Lists and monads
Kevin Jardine wrote: But as I said, that is just an example. I keep wanting to apply the usual list tools but find that they do not work inside a monad. I find myself wishing that f (m [a]) just automatically returned m f([a]) Are you looking for these? import Data.Traversable as T T.sequence :: (T.Traversable t, Monad m) = t (m a) - m (t a) T.mapM :: (T.Traversable t, Monad m) = (a - m b) - t a - m (t b) -- N.B. T.mapM ~ (T.sequence . fmap) without me needing to do anything but I expect that there are reasons why that is not a good idea. Not all functors can be distributed over arbitrary monads, so not a good idea is more like not always possible or here be dragons (fluffy, intriguing, and pretty dragons to be sure; but probably deeper than the answer you were looking for). In addition to Applicative, the Traversable and Foldable classes should be key tools in your toolbox. They take a number of functions typically restricted to lists and generalize them to different functors, often with Applicatives or Monads involved. The Typeclassopedia should have more on them. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monoids and monads
Henning Thielemann wrote:
However the applicative functor laws from
http://www.haskell.org/ghc/docs/6.12.2/html/libraries/base-4.2.0.1/Control-Applicative.html
are quite unintuitive and the proofs are certainly not very
illustrative.
I always found it more illustrative to break it down and talk about
pointed functors, where 'return' is trivial in 'fmap' (forgive the Coq
syntax):
fmap_pointed
: forall {A B : Type} (f : A - B) (a : A)
, f $ return a = return $ f a
And then you only need three laws, the obvious ones:
app_return_left
: forall {A B : Type} (f : A - B) (xa : F A)
, return f * xa = f $ xa
app_return_right
: forall {A B : Type} (xf : F (A - B)) (a : A)
, xf * return a = ($a) $ xf
app_compose
: forall {A B C : Type}
, forall (xf : F (B - C)) (xg : F (A - B)) (xa : F A)
, compose $ xf * xg * xa = xf * (xg * xa)
That is, we have that 'return' is (in the appropriate sense) the left
and right identity for (*), which allows us to apply fmap_pointed to
reduce (*) into ($). Since only one of the arguments has a
non-trivial structure, that's the structure we use for ($).
And then we have (again in the appropriate sense) associativity of
composition. Which is really just to say that composition from the pure
world is preserved as composition in the applicative world.
The other two laws (app_identity : ..., return id $ xa = xa) and
(app_homomorphism : ..., return f * return a = return (f a)) follow
directly from fmap_pointed. Or conversely, given these five laws we can
always prove fmap_pointed.
--
Live well,
~wren
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Re: [Haskell-cafe] An experimental Zipper using Thrists and first-class Labels. Help or thoughts?
On Tue, Jul 27, 2010 at 1:59 AM, Jason Dagit da...@codersbase.com wrote:
On Mon, Jul 26, 2010 at 9:00 PM, Brandon Simmons
brandon.m.simm...@gmail.com wrote:
I had the idea for a simple generic Zipper data structure that I
thought would be possible to implement using type-threaded lists
provided by Gabor Greif's thrist package:
http://hackage.haskell.org/package/thrist
...and the fclabels package by Sebastiaan Visser, Erik Hesselink,
Chris Eidhof and Sjoerd Visscher:
http://hackage.haskell.org/package/fclabels
It would (ideally) work as follows:
- the zipper would consist simply of a tuple:
(type threaded list of constructor sections , current context)
- in the type threaded list we store functions (constructor with hole
- complete constructor), so the
one hole context is represented as a lambda expression where the
free variable will be filled
by the current context (the snd of the tuple)
- we go down through our structure by passing to our `moveTo`
function a first-class label
corresponding to the constructor we want to descend into. `moveTo`
uses this both as a getter
to extract the next level down from the current level, and as a
setter to form the lambda expression
which acts as the constructor with a piece missing
- going up means popping the head off the thrist and applying it to
the current context, making that
the new context, exiting the zipper would be a fold in the same manner
After throwing together a quick attempt I realized that I'm not sure
if it would be possible to make the `moveUp` function type-check and
be usable. I'm still new to GADTs, existential types, template haskell
etc. and am stuck.
Here is the code I wrote up, which doesn't currently compile:
-- START CODE
---
{-# LANGUAGE TypeOperators, GADTs #-}
module ZipperGenerator
(
viewC --lets user pattern match against context
, moveTo
, moveUp
, genZippers
, zipper
, unzipper
, (:-)
, ZipperGenerator
, Zipper
) where
-- these provide the secret sauce
import Data.Record.Label
import Data.Thrist
import Language.Haskell.TH
type ZipperGenerator = [Name] - Q [Dec]
-- the Template Haskell function that does the work of generating
-- first-class labels used to move about the zipper:
genZippers :: ZipperGenerator
genZippers = mkLabels
-- hide the innards:
newtype Zipper t c = Z (Thrist (-) c t, c)
-- returns the current context (our location in the zipper) for pattern
-- matching and inspection:
viewC :: Zipper t c - c
viewC (Z(_,c)) = c
-- takes a first-class label corresponding to the record in the current
context
-- that we would like to move to:
moveTo :: (c :- c') - Zipper t c - Zipper t c'
moveTo lb (Z(thr,c)) = Z (Cons (\a- set lb a c) thr , get lb c)
-- backs up a level in the zipper, returning `Nothing` if we are already
at the
-- top level:
moveUp :: Zipper t c - Maybe (Zipper t b)
moveUp (Z (Nil,_)) = Nothing
moveUp (Z (Cons f thr,c)) = Just $ Z (thr, f c)
-- create zipper with focus on topmost constructor level:
zipper :: t - Zipper t t
zipper t = Z (Nil,t)
-- close zipper
unzipper :: Zipper t c - t
unzipper (Z(thr,c)) = undefined --foldThrist ($) id thr c
Hmm...I think you just need to change ($) to (.). I haven't tested it.
But, if you have Thrist (-) c t, then what you have is a transformation
from c to t, or more simply, c - t. So, conceptually at least, you just
need to compose the elements in your Thrist. ($) is application, but in the
space of functions it is identity. So, if you think the elements in your
thrist as being values in the space of functions, you're asking for a right
fold that is like, v1 `id` (v2 `id` (v3 `id` ...), which I hope you agree
doesn't make that much sense. So try this:
unzipper (Z(thr,c)) = foldThrist (.) id thr c
In the darcs source we use our own custom thrists for storing sequences of
patches. We have two variants, forward lists (FL) and reverse lists (RL).
In our parlance, we have foldlFL defined thusly:
foldlFL :: (forall w y. a - b w y - a) - a - FL b x z - a
foldlFL _ x NilFL = x
foldlFL f x (y::ys) = foldlFL f (f x y) ys
We don't use Control.Arrow, so in our notation the 'b' in the type signature
plays the same role as (~) but in prefix notation, of course. And we use
(::) instead of Cons. It's supposed to look like normal list cons but with
an arrow pointing forward. The cons for RL is (::). Perhaps we should use
arrow though, as I think that looks pretty nice.
For comparison, here is the definition of foldThrist:
foldThrist :: (forall i j k . (i ~ j) - (j ~ k) - (i ~ k))
- c ~ c
- Thrist (~) a c
- a ~ c
foldThrist _ v Nil = v
foldThrist f v (Cons h t) = h `f` (foldThrist f v t)
As you can see, our fold is a left fold and the thrist fold is a right fold.
I don't think a left fold will help you here, but you might
Re: [Haskell-cafe] Haskell Forum
Magnus Therning wrote: On 26/07/10 22:01, Andrew Coppin wrote: So I'm told. But it appears that some people believe that NNTP *is* Usenet, which is not the case. I use NNTP almost every single day, but I've never seen Usenet in my life... So you've only ever been on private NNTP servers then, never browsed through comp.* or sci.*? I don't even know what they are. (Except that now, by inference, I can guess they're something to do with Usenet.) For example, Microsoft has a private NNTP server for technical support. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Forum
John Meacham wrote: There already is an NNTP - mailing list gateway via gmane that gives a nice forumy and threaded web interface for those with insufficient email readers. Adding a completely different interface seems unnecessary and fragmentary. Trouble is, you can't use it like just another NNTP server. If you have a forum powered by NNTP, you can casually throw in a hey, nice one time comment as a reply to part of a thread, and only people interested in that thread have to see your message (or download it, for that matter). If you do that on a mailing list, all 700+ subscribers get a copy of your email. And, usually, they're not very amused about it. With SMTP, you can only really say something if it's really, really worth saying. Otherwise it just gets too noisy. That's the trouble with a mailing list; it's everyone talking to everyone. NNTP has real threading, and a central place where all the messages can be redownloaded from incrimentally, and it doesn't get eaten by your ISP's spam filter, and and and... Still, I know from experience that I am the only person here who appreciates these virtues. Everybody else seems quite happy with a crude SMTP system, so... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Int and ByteStrings
Hey all, Is there a library function (f :: [Int] - ByteString) such that it's prefix-preserving, and platform independent? GHC-only is fine for now. There are a bunch of functions of that type, but I need those guarantees and I'm hoping someone else has already done it. If there isn't one for Int, has someone already made a package that offers IntMap on Word32, Word64, etc? -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Forum
From my experience once a forum pops up the mailing list dies. -- Mihai Maruseac ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Actors and message-passing a la Erlang
I've found that I like Erlang's pattern matching for sorting through different kinds of data payloads, but that I prefer to use typed data channels per Limbo, Go, Plan 9's thread and messaging libraries etc. I've often wanted an Erlang with static typing to get this capability. Actually you are right. And it is not much of a chore to write: data MyMessages = Something XXX | SomethingElse YYY ZZZ | Stop | ... given that it ensures your message-passing is correct at compile time. It gives you an Actor type like: data Actor msgIn msgOut Where msgIn is the type of received messages (Erlang's 'receive') and msgOut the type of sent messages (Erlang's '!'). 2010/7/27 David Leimbach leim...@gmail.com On Tue, Jul 27, 2010 at 5:27 AM, Stefan Schmidt stefanschmid...@googlemail.com wrote: Hi Yves, You say that With the help of this library it is possible to build Erlang-Style mailboxes, but how would you solve the issue of static typing? this wasn't an issue for me because I wanted as much type checking as possible. In many implementations, you have an implicit contract between the sender and the receiver process. In this case, the contract is explicit and the compiler can tell me if I'm trying to send or receive wrong data. I've found that I like Erlang's pattern matching for sorting through different kinds of data payloads, but that I prefer to use typed data channels per Limbo, Go, Plan 9's thread and messaging libraries etc. I've often wanted an Erlang with static typing to get this capability. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Lists and monads
Looks interesting. I've also come across Data.List.Class: http://hackage.haskell.org/packages/archive/generator/0.5.1/doc/html/Data-List-Class.html Has anyone used that? Kevin On Jul 27, 6:02 pm, wren ng thornton w...@freegeek.org wrote: Kevin Jardine wrote: But as I said, that is just an example. I keep wanting to apply the usual list tools but find that they do not work inside a monad. I find myself wishing that f (m [a]) just automatically returned m f([a]) Are you looking for these? import Data.Traversable as T T.sequence :: (T.Traversable t, Monad m) = t (m a) - m (t a) T.mapM :: (T.Traversable t, Monad m) = (a - m b) - t a - m (t b) -- N.B. T.mapM ~ (T.sequence . fmap) without me needing to do anything but I expect that there are reasons why that is not a good idea. Not all functors can be distributed over arbitrary monads, so not a good idea is more like not always possible or here be dragons (fluffy, intriguing, and pretty dragons to be sure; but probably deeper than the answer you were looking for). In addition to Applicative, the Traversable and Foldable classes should be key tools in your toolbox. They take a number of functions typically restricted to lists and generalize them to different functors, often with Applicatives or Monads involved. The Typeclassopedia should have more on them. -- Live well, ~wren ___ Haskell-Cafe mailing list haskell-c...@haskell.orghttp://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] Re: Haskell Forum
On Tue, Jul 27, 2010 at 07:01:45PM +0100, Andrew Coppin wrote: If you have a forum powered by NNTP, you can casually throw in a hey, nice one time comment as a reply to part of a thread, and only people interested in that thread have to see your message (or download it, for that matter). ... Still, I know from experience that I am the only person here who appreciates these virtues. Everybody else seems quite happy with a crude SMTP system, so... IOW, if people use the proper and well known features of NNTP it would be a better world than the one we have were people do not use proper and well known features of SMTP. As it stands, even with SMTP you get people who post new message topics as replies to existing threads, as well as people who *somehow* reply to a thread but do not include In-Reply-To or References headers so threading is broken. I have no reason to think people would not do the same broken things with NNTP, foiling my plans for following some threads and ignoring others. As long as people are sharing opinions, I'll add mine: * If the mailing lists go away I will probably not switch to whatever replaces it. * A list - forum gateway is fine, as long as the message IQ doesn't drop through the floor as a result. This fear comes from personal, anecdotal evidence. YMMV. * No opinion either way on List - NNTP gateway. -- Darrin Chandler| Phoenix BSD User Group | MetaBUG dwchand...@stilyagin.com | http://phxbug.org/ | http://metabug.org/ http://www.stilyagin.com/ | Daemons in the Desert | Global BUG Federation ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Int and ByteStrings
wren: Hey all, Is there a library function (f :: [Int] - ByteString) such that it's prefix-preserving, and platform independent? GHC-only is fine for now. There are a bunch of functions of that type, but I need those guarantees and I'm hoping someone else has already done it. should be possible to write using Data.Binary. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] transform function for a GADT
I'd add another parameter to the ExprType class and give an explicit representation to your types. data EType a where EInt :: EType Int EBool :: EType Bool data TypeEq a b where Refl :: TypeEq x x eqEType :: ExprType a - ExprType b - Maybe (TypeEq a b) eqEType EInt EInt = Just Refl eqEType EBool EBool = Just Refl eqEType _ _ = Nothing class ExprType a where toExpr :: a - Expr a eType :: EType a eTypeOf :: Expr a - EType a eTypeOf (Bin _) = EBool eTypeOf (Num _) = EInt eTypeOf (_ :+: _) = EInt -- etc. transform :: (ExprType a, ExprType b) = (Expr b - Expr b) - Expr a - Expr a transform = transform' eType -- uses LANGUAGE PatternGuards transform' :: EType b - (Expr b - Expr b) - Expr a - Expr a transform' t f e | Just Refl - eqEType t (eTypeOf e) = f e -- this is the magic line transform' t f (Bin b) = Bin b tranfsorm' t f (Num i) = Num i transform' t f (e1 :+: e2) = transform' t f e1 :+: transform' t f e2 -- etc. The magic line checks if the type of the expression matches the type of the function, and if so, applies it. -- ryan On Tue, Jul 27, 2010 at 8:28 AM, Ozgur Akgun ozgurak...@gmail.com wrote: Café, I've tried several things already, but I am not including any of them for now. My question is, how would you define the 'transform' function for a GADT, say the one in the linked gist: http://gist.github.com/492364 (also attached to this e-mail) To be concise, I want 'transform' to apply the transformation function (its first parameter) to every immidiate child of its second parameter as long as the types match. Similar to what the 'tranform' function of Uniplate does for normal ADTs. (But just one level, so I guess it is more similar to the 'descend' of Uniplate. See http://hackage.haskell.org/packages/archive/uniplate/1.2.0.1/doc/html/Data-Generics-UniplateStr.html) I think I got closest to a sensible solution using multi-param type classes, and defining many instances for different combinations of ExprType's but still there were problems. Waiting for suggestions and/or insights. Best, Ozgur Akgun ___ 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] Parsec Best Practices examples
Hi, All. I have a compiler written in Parsec and Haskell for a DSL. It's quite rudimentary since I made it for my own use only. I would like to make it useable by a slightly wider circle. For this, I need better error reporting. Currently, it terminates after finding one syntax error. I would like to detect as many syntax errors as possible and report them before terminating. Are there any best practices examples of how to do this available? It seems like something many people would have solved already. Cheers, David David F. 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] Re: Haskell Forum
Darrin Chandler wrote: IOW, if people use the proper and well known features of NNTP it would be a better world than the one we have were people do not use proper and well known features of SMTP. SMTP is designed for delivering messages point-to-point. If your email provider incorrectly marks half the list traffic as spam, you can't read it. If your PC dies and you lose all your email, you cannot get it back again. If you hit reply, it only replies to the one person who wrote the message, not to the list. And every person has to download every single message ever sent. Because, let's face it, all a list server does is receive emails and then re-send them to everybody. If your mail system isn't operational at the moment when the email is sent, you'll never receive it and cannot ever get it afterwards. NNTP is designed to deliver list traffic. You can tell your news reader to download messages posted before you joined the group (which is impossible with a mailing list). If your PC dies, you can just re-download all the messages again. Threading actually works properly. You only need download the message bodies that you're actually interested in. And so on. As it stands, even with SMTP you get people who post new message topics as replies to existing threads, as well as people who *somehow* reply to a thread but do not include In-Reply-To or References headers so threading is broken. I have no reason to think people would not do the same broken things with NNTP, foiling my plans for following some threads and ignoring others. I constantly have trouble with this mailing list. Even gmane can't seem to thread it properly. But I've never had any trouble with threading in any NNTP group, ever. [Well, apart from that stupid Thunderbird bug they still haven't fixed yet. But that's a client bug. Use a different client and it goes away.] * If the mailing lists go away I will probably not switch to whatever replaces it. ...nd this is why no matter how superior it is, this list will never get updated. * A list - forum gateway is fine, as long as the message IQ doesn't drop through the floor as a result. This fear comes from personal, anecdotal evidence. YMMV. Uh, why would that happen? I guess if it went to a web forum there'd by a greater danger of that maybe. But heck, we don't have much trouble on IRC, and that's notorious for the kind of trolls it tends to attract... * No opinion either way on List - NNTP gateway. As I say, there already is one. But because 98% of everybody uses this list as an email list, you can't go using it like it's a news group. You'll just get yelled at. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Forum
On 2010-07-27 19:59 +0100, Andrew Coppin wrote: Darrin Chandler wrote: IOW, if people use the proper and well known features of NNTP it would be a better world than the one we have were people do not use proper and well known features of SMTP. SMTP is designed for delivering messages point-to-point. If your email provider incorrectly marks half the list traffic as spam, you can't read it. This has nothing to do with SMTP, and everything to do with your email provider being worthless. If your PC dies and you lose all your email, you cannot get it back again. Assuming you've never heard of list archives or backups, sure. If you hit reply, it only replies to the one person who wrote the message, not to the list. Every mail client worth its salt has a 'reply to group' function, which performs as advertised. In fact, I can't even name a single one that does not have this function. And every person has to download every single message ever sent. Because, let's face it, all a list server does is receive emails and then re-send them to everybody. This point is valid, but not really relevant since the advent of DSL. A week's traffic on linux-kernel is about 30 megabytes. Haskell-cafe is about 4. If your mail system isn't operational at the moment when the email is sent, you'll never receive it and cannot ever get it afterwards. This is not an accurate reflection of reality. I constantly have trouble with this mailing list. Even gmane can't seem to thread it properly. But I've never had any trouble with threading in any NNTP group, ever. Mutt seems to have no trouble threading it properly. I haven't encountered an issue with gmane and this list, although admittedly I don't use it often. [Well, apart from that stupid Thunderbird bug they still haven't fixed yet. But that's a client bug. Use a different client and it goes away.] The same can be said about email threading. -- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Forum
On Tue, Jul 27, 2010 at 07:59:40PM +0100, Andrew Coppin wrote: NNTP is ... It's all true. I used nntp extensively in the 90s. I never emo-quit, I just stopped using it over time due to waning ISP support and other reasons made it more of a pain. I have nothing against nntp as a protocol, but I have my reasons for no longer using it. I constantly have trouble with this mailing list. Even gmane can't seem to thread it properly. But I've never had any trouble with threading in any NNTP group, ever. Hmm. I don't see this mailing list as unusual in any way wrt threading, except that most people here actually *do* reply properly, most of the time. * If the mailing lists go away I will probably not switch to whatever replaces it. ...nd this is why no matter how superior it is, this list will never get updated. Pretty much. * A list - forum gateway is fine, as long as the message IQ doesn't drop through the floor as a result. This fear comes from personal, anecdotal evidence. YMMV. Uh, why would that happen? I guess if it went to a web forum there'd by a greater danger of that maybe. But heck, we don't have much trouble on IRC, and that's notorious for the kind of trolls it tends to attract... In my experience, either a web forum is actively maintained and moderated or it becomes a troll magnet. Trolls can live anywhere, but they prefer caves, under bridges, and web forums. People on this list who desire a forum are not the problem, and I certainly don't want to imply that. As for IRC, I think freenode/#haskell has enough quality and quantity to keep the trolls down. I haven't had much troll problems on freenode, though I'm sure others could share some tales. * No opinion either way on List - NNTP gateway. As I say, there already is one. But because 98% of everybody uses this list as an email list, you can't go using it like it's a news group. You'll just get yelled at. I find it surprising that you'd get yelled at, but I don't really know. -- Darrin Chandler| Phoenix BSD User Group | MetaBUG dwchand...@stilyagin.com | http://phxbug.org/ | http://metabug.org/ http://www.stilyagin.com/ | Daemons in the Desert | Global BUG Federation ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell at CERN
Hello I'm wondering is there any haskellers in CERN? Given quality and usability of software there must be people looking for better alternatives. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] fine control of bytestring streaming
Hi, I´m streaming content using lazy bytestrings in a web application. The problem is that the output comes in huge blobs (presumably of 32k) one at a time. This is good for some purposes, but not for console-like interfaces or runtime log visualization. (one of my purposes is to web-alize ghci. I know that this can be done without streaming the standard output, but I want it that way). I can not control when the IO bytestring primitives flush the data to the stream, because this is not part of my application (nor does it should do it). I suppose here that it is in a chunk by chunk basis. But maybe I misinterpreted something or everything. I use the package hack with the server hack-handler-simpleserver. this serves does Data.ByteString.hPut the bytestring content... I use mappend to add content to the stream. mappend uses append which uses. foldrChunks which seems not to compact two bytestrings in max size chunks . So I do not know what happens. The question is: are there some way to control bytestring streaming?. Can It be done without the stream handler? Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] fine control of bytestring streaming
On Tue, 27 Jul 2010, Alberto G. Corona wrote: The question is: are there some way to control bytestring streaming?. Can It be done without the stream handler? I think there is a function that converts a lazy ByteString to a list of strict ByteStrings, that should work without copying the chunk data around. On this chunk list you can do all kind of manipulations, like merging adjacent small chunks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] new Cabal user question -- installing to Haskell Platform on Windows network drive?
Rogan: Thanks very much. I began by downloading the latest gtk+ bundle from http://www.gtk.org/download-windows.html The instructions there said to just copy the files to any dir and add its ...\gtk\bin dir to my PATH, which I did, so that worked okay without admin privs. Given that I need to use these tools on a network drive (H:), and not C:, I have installed the Platform and gtk to: H:\proc\tools\Haskell Platform and H:\proc\tools\gtk (My H: is a hdd, not usb; and I am trying to do all this without admin privs, which is working fine so far.) The gtk tests: pkg-config --cflags gtk+-2.0 and gtk-demo run fine. Great! Anyone: So, I am trying to use cabal (for the first time), on a Windows XP system/network. I need to keep everything on H:, and not use C:. The only copy of cabal I have is what came with the Platform: H:\proc\tools\Haskell Platform\2010.1.0.0\lib\extralibs\bin\cabal.exe. I placed that bin dir in my PATH and tried a cabal update. (Does is matter what my current dir is, when I use cabal?) It said: H:\proc\dev\cmdcabal update Config file path source is default config file. Config file C:\Documents and Settings\pschmitz\Application Data\cabal\config not found. Writing default configuration to C:\Documents and Settings\pschmitz\Application Data\cabal\config Downloading the latest package list from hackage.haskell.org Note: there is a new version of cabal-install available. To upgrade, run: cabal install cabal-install So, by default, cabal wants to put its config and updates on C:. I looked at C:\Documents and Settings\pschmitz\Application Data\cabal\config It has various references to C:, some commented out. E.g.: remote-repo-cache: C:\Documents and Settings\pschmitz\Application Data\cabal\packages build-summary: C:\Documents and Settings\pschmitz\Application Data\cabal\logs\build.log install-dirs user -- prefix: C:\\Documents and Settings\\pschmitz\\Application Data\\cabal etc. I also reviewed the Cabal User's Guide, including section 4.1.2.2 Paths in the simple build system which has a table with command line switches and pathname defaults for Windows including: --prefix (global installs with the --global flag) C:\ProgramFiles\Haskell and --prefix (per-user installs with the --user flag) C:\DocumentsAndSettings\user\ApplicationData\cabal Given that I want to keep everything on H:, and assuming that I don't want to place the Cabal configs and updates in the Platform tree (H:\proc\tools\Haskell Platform), I would _like_ to create a dir such as H:\proc\tools\cabal to hold everything that Cabal would normally put on C:. *** I'm afraid I'm having trouble figuring out how to accomplish this. Is there (hopefully) a combination of cabal command line switches that will create a new config file over on H: for me, or must I edit the config file directly and move it to H:? And then, how do I invoke cabal each time, to get it to use its tree on H: (and ignore C:) ? Thanks (very much) in advance. -- Peter Schmitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Error Monad and strings
Reading the Control.Monad.Error documentation, I see that the Error class has noMsg and strMsg as its only two functions. Now, I understand that you can define your own Error instances such as in example 1 of the documentation, so why the need to always support strings via noMsg/strMsg ? What uses these? And if in my code, I will never throw an error with a string, am I supposed to implement these functions and then ignore them? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error Monad and strings
It is for the very annoying reason that in order for Error to be a monad it has to implement the fail method, which means it has to know how to turn an arbitrary string into a value of your error type. Cheers, Greg On 07/27/10 15:32, Gerald Gutierrez wrote: Reading the Control.Monad.Error documentation, I see that the Error class has noMsg and strMsg as its only two functions. Now, I understand that you can define your own Error instances such as in example 1 of the documentation, so why the need to always support strings via noMsg/strMsg ? What uses these? And if in my code, I will never throw an error with a string, am I supposed to implement these functions and then ignore them? ___ 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] Error Monad and strings
The strMsg method is used to implement the fail method in the
resulting method, and calls to fail might be inserted into your code
even if you don't explicitly call it. An example in GHCi:
Prelude :m + Control.Monad.Error
Prelude Control.Monad.Error do { Just x - return Nothing ; return
x } :: Either String Int
Left Pattern match failure in do expression at interactive:1:5-8
Note that in the Either String monad, failStr is equal to Left.
On 2010 July 27, at 15:32, Gerald Gutierrez wrote:
Reading the Control.Monad.Error documentation, I see that the Error
class has noMsg and strMsg as its only two functions.
Now, I understand that you can define your own Error instances such
as in example 1 of the documentation, so why the need to always
support strings via noMsg/strMsg ? What uses these? And if in my
code, I will never throw an error with a string, am I supposed to
implement these functions and then ignore them?
___
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Re: [Haskell-cafe] Error Monad and strings
On Tue, Jul 27, 2010 at 3:57 PM, Dietrich Epp d...@zdome.net wrote:
The strMsg method is used to implement the fail method in the resulting
method, and calls to fail might be inserted into your code even if you
don't explicitly call it. An example in GHCi:
Prelude :m + Control.Monad.Error
Prelude Control.Monad.Error do { Just x - return Nothing ; return x } ::
Either String Int
Left Pattern match failure in do expression at interactive:1:5-8
On 2010 July 27, at 15:32, Gerald Gutierrez wrote:
Reading the Control.Monad.Error documentation, I see that the Error class
has noMsg and strMsg as its only two functions.
Now, I understand that you can define your own Error instances such as in
example 1 of the documentation, so why the need to always support strings
via noMsg/strMsg ? What uses these? And if in my code, I will never throw an
error with a string, am I supposed to implement these functions and then
ignore them?
I see. So strings must be supported in the case of a bug which cannot be
caught at compile time? In other words, if I get an error with a string, I'm
pretty much guaranteed it is a bug, i.e. a pattern match error as the fail
documentation says.
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Re: [Haskell-cafe] Error Monad and strings
I'll say yes, a pattern match failure is a bug. This is one of the
great debates in the language: whether all pattern matching code
should be guaranteed complete at compile time or not. However, any
function you call which returns a result in your monad could
theoretically call fail if it was written that way. Data.Map.lookup
used to call fail when it could not find a key, but that got changed.
If you don't want to catch these errors in your monad, you can write
your own monad (or monad transformer). For example:
newtype ErrorCode = ErrorCode Int deriving Show
newtype ErrorCodeT m a = ErrorCodeT { runErrorCodeT :: m (Either
ErrorCode a) }
instance Monad m = Monad (ErrorCodeT m) where
return = ErrorCodeT . return . Right
a = b = ErrorCodeT $ do
m - runErrorCodeT a
case m of
Left err - return $ Left err
Right x - runErrorCodeT $ b x
fail = ErrorCodeT . fail
failWithCode :: Monad m = Int - ErrorCodeT m a
failWithCode = ErrorCodeT . return . Left . ErrorCode
There's probabaly a library somewhere which does this already.
On 2010 July 27, at 16:08, Gerald Gutierrez wrote:
I see. So strings must be supported in the case of a bug which
cannot be caught at compile time? In other words, if I get an error
with a string, I'm pretty much guaranteed it is a bug, i.e. a
pattern match error as the fail documentation says.
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[Haskell-cafe] Re: Haskell Forum
Kevin Jardine kevinjard...@gmail.com writes: On Jul 26, 6:45 pm, Nick Bowler nbow...@elliptictech.com wrote: Since when do mailing lists not have threading? Web forums with proper support for threading seem to be few and far apart. Most of the email clients I'm familiar with don't support threaded displays and most of the web forums I'm familiar with do (although the feature is not always switched on). In my experience the debate between mailing list vs. web forum can become very emotional (especially when discussed via a mailing list) and I don't think it is that productive. Some people like one, some people like the other. That's why I think that it is useful to give people a choice. One problem with creating a Web forum for a topic supported by a community that already chiefly communicates via a mailing list is that cross-referencing/cross-posting can become difficult. Suppose that somebody addresses a topic that has already been introduced on the mailing list on the forum, and that someone on mailing list then sees this topic and wants to respond. Should he/she respond on the mailing list, or the forum? How about follow-ups? What if he/she wishes to restrict follow-ups to either the forum or the mailing list? Conversely, suppose that somebody addresses a topic that has already been introduced on the forum on the mailing list, and that someone on the forum then sees this topic and wants to respond. What then? What happens if the forum users see some of the content as appropriate for the mailing list, but not for the forum? The only viable solution is to have every mailing list post forwarded to the forum and vice-versa, and have a moderator for the forum filter out posts containing content that is deemed inappropriate for the Web. But then this leads to an additional problem: What if some users on the mailing list deem content that has been filtered out by the moderator as appropriate for discussion on both forums, while the forum users consider it as inappropriate it? Consider the following sample discussion (which I just wrote for the purpose of this discussion, but which actually discusses a possible topic), which contains issues of technical terms containing scatological (i.e., dirty) language, multiple levels of indentation, representation of URLs, and article length (please ignore this example if you feel upset by technical terms that contain scatological terms): subject: A Comparison of Whitespace in Haskell and brainfuck I discovered an article (see http://en.wikipedia.org/wiki/Brainfuck) on the brainfuck programming language (not to be confused with the Brain Fuck Scheduler (BFS) (see http://en.wikipedia.org/wiki/Brain_Fuck_Scheduler)) that introduced a sample Hello World! program: The following program prints Hello World! and a newline to the screen: + + initialize counter (cell #0) to 10 [ use loop to set the next four cells to 70/100/30/10 + ++ add 7 to cell #1 + + add 10 to cell #2 +++ add 3 to cell #3 + add 1 to cell #4 - decrement counter (cell #0) ] ++ . print 'H' + . print 'e' + ++ . print 'l' . print 'l' +++ . print 'o' ++ . print ' ' + + + . print 'W' . print 'o' +++ . print 'r' - - . print 'l' - --- . print 'd' + . print '!' . print '\n' For readability, this code has been spread across many lines and blanks and comments have been added. Brainfuck ignores all characters except the eight commands +-[],. so no special syntax for comments is needed. The code could just as well have been written as: ++[+-]++.+.+++..+++.++.+++..+++.--..+.. By comparison, a corresponding article on Haskell (see http://en.wikipedia.org/wiki/Haskell_(programming_language)) provided the following Haskell alternative:: The following is a Hello world program written in Haskell (note that except for the last line all lines can be omitted): module Main where main :: IO () main = putStrLn Hello, World! I became curious about the use of whitespace in the brainfuck example, and decided to see if the Haskell code could also be written more compactly. While doing some research on this topic, I discovered a Wikibook article (see http://en.wikibooks.org/wiki/Haskell/Indentation) that discussed indentation in Haskell, and discovered that it was indeed entirely possible to write compact code in Haskell, using semicolon[s] to separate things and curly braces to group them back. The following four rules were provided to
[Haskell-cafe] Re: Haskell Forum
Nick Bowler nbow...@elliptictech.com writes: On 13:58 Mon 26 Jul , John Meacham wrote: There already is an NNTP - mailing list gateway via gmane that gives a nice forumy and threaded web interface for those with insufficient email readers. Adding a completely different interface seems unnecessary and fragmentary. http://news.gmane.org/gmane.comp.lang.haskell.cafe Ah, I didn't realise the gmane web interface supported followups (I knew the NNTP interface did, and mentioned this elsewhere in this thread). Looks like we've already got a web forum, then, so I guess there's nothing to do! :) Same here. Why don't we just use this interface, which already exists? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error Monad and strings
On Tue, Jul 27, 2010 at 6:29 PM, Dietrich Epp d...@zdome.net wrote: I'll say yes, a pattern match failure is a bug. This is one of the great debates in the language: whether all pattern matching code should be guaranteed complete at compile time or not. However, any function you call which returns a result in your monad could theoretically call fail if it was written that way. Data.Map.lookup used to call fail when it could not find a key, but that got changed. I've always thought that being able to write: catMaybes :: [Maybe a] - [a] catMaybes xs = [ x | Just x - xs ] is really cool, which relies on: fail _ = [] being in the Monad instance for List. But I would give that up for getting fail out of Monad. We can alway re-implement catMaybes. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Chart package segfaults when rendering to window
On Mon, 26 Jul 2010 21:54:16 -0700 Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Can you boil this down to some simple example code? Are you using a recent version of Chart? And your definition of latest gtk2hs is 11, right? How about your gtk+ C library, it what? 2.20? I can run any of the examples from the home page that render to screen. the AM chart is the one I'm using. BTW, the AM chart has a bug. It does not include the proper color modules and needs a (opaque color) instead of just color. gtk2hs is 11 gtk+ C library appars to be (debian package) 2.20.1 I was wondering if anybody has been using Chart and may have seen the same thing. Nope, not me. Yep, figured I'd be suffering alone. Brian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Need Control.Monad.State
How do I import Control.Monad.State? I see this note in http://en.wikibooks.org/wiki/Haskell/Understanding_monads/State Note: in some package systems used for GHC, the Control.Monad.State module is in a separate package, usually indicated by MTL (Monad Transformer Library). Michael ===rand.hs == import Control.Monad.State type GeneratorState = State StdGen rollDie :: GeneratorState Int rollDie = do generator - get let( value, newGenerator ) = randomR (1,6) generator put newGenerator return value === [mich...@localhost ~]$ ghci rand GHCi, version 6.12.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. rand.hs:1:7: Could not find module `Control.Monad.State': Use -v to see a list of the files searched for. Failed, modules loaded: none. Prelude ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
On 28 July 2010 12:39, michael rice nowg...@yahoo.com wrote: How do I import Control.Monad.State? Install and use the mtl library (comes with the Haskell platform), monads-fd (almost identical API to mtl; the point of this is that mtl uses some extension: the non-extension bits are in the transformers library and monads-fd extends transformers by using extensions to implement mtl functionality) or monads-tf (a different approach to what monads-fd does using different extensions). To check if you have mtl installed (substitute the other package names if necessary): ghc-pkg list mtl If it isn't installed, you can use cabal-install to install it: cabal install mtl -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
[mich...@localhost ~]$ ghc-pkg list mtl /usr/lib/ghc-6.12.1/package.conf.d [mich...@localhost ~]$ Installed? Michael --- On Tue, 7/27/10, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: From: Ivan Miljenovic ivan.miljeno...@gmail.com Subject: Re: [Haskell-cafe] Need Control.Monad.State To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, July 27, 2010, 10:51 PM On 28 July 2010 12:39, michael rice nowg...@yahoo.com wrote: How do I import Control.Monad.State? Install and use the mtl library (comes with the Haskell platform), monads-fd (almost identical API to mtl; the point of this is that mtl uses some extension: the non-extension bits are in the transformers library and monads-fd extends transformers by using extensions to implement mtl functionality) or monads-tf (a different approach to what monads-fd does using different extensions). To check if you have mtl installed (substitute the other package names if necessary): ghc-pkg list mtl If it isn't installed, you can use cabal-install to install it: cabal install mtl -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
On 28 July 2010 13:03, michael rice nowg...@yahoo.com wrote: [mich...@localhost ~]$ ghc-pkg list mtl /usr/lib/ghc-6.12.1/package.conf.d [mich...@localhost ~]$ Installed? No; if it was installed it would specify a version. Michael --- On Tue, 7/27/10, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: From: Ivan Miljenovic ivan.miljeno...@gmail.com Subject: Re: [Haskell-cafe] Need Control.Monad.State To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, July 27, 2010, 10:51 PM On 28 July 2010 12:39, michael rice nowg...@yahoo.com wrote: How do I import Control.Monad.State? Install and use the mtl library (comes with the Haskell platform), monads-fd (almost identical API to mtl; the point of this is that mtl uses some extension: the non-extension bits are in the transformers library and monads-fd extends transformers by using extensions to implement mtl functionality) or monads-tf (a different approach to what monads-fd does using different extensions). To check if you have mtl installed (substitute the other package names if necessary): ghc-pkg list mtl If it isn't installed, you can use cabal-install to install it: cabal install mtl -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
On Wed, Jul 28, 2010 at 12:04 AM, Ivan Miljenovic ivan.miljeno...@gmail.com wrote: On 28 July 2010 13:03, michael rice nowg...@yahoo.com wrote: [mich...@localhost ~]$ ghc-pkg list mtl /usr/lib/ghc-6.12.1/package.conf.d [mich...@localhost ~]$ Installed? No; if it was installed it would specify a version. For example: $ ghc-pkg list mtl /usr/lib64/ghc-6.12.3/package.conf.d mtl-1.1.0.2 -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
See below. Lot's of warnings. Is the install OK? If so, can I use the same
*import*?
Michael
--- On Tue, 7/27/10, Ivan Miljenovic ivan.miljeno...@gmail.com wrote:
If it isn't installed, you can use cabal-install to install it:
cabal install mtl
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
[mich...@localhost ~]$ cabal install mtl
Resolving dependencies...
Downloading mtl-1.1.0.2...
Configuring mtl-1.1.0.2...
Preprocessing library mtl-1.1.0.2...
Building mtl-1.1.0.2...
[ 1 of 21] Compiling Control.Monad.Identity ( Control/Monad/Identity.hs,
dist/build/Control/Monad/Identity.o )
Control/Monad/Cont.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Cont/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Error.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Error/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Identity.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
Control/Monad/List.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/RWS/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/RWS/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Reader.hs:2:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Reader/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/State/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/State/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
[ 2 of 21] Compiling Control.Monad.Writer.Class (
Control/Monad/Writer/Class.hs, dist/build/Control/Monad/Writer/Class.o )
Control/Monad/Writer/Class.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
[ 3 of 21] Compiling Control.Monad.Error.Class ( Control/Monad/Error/Class.hs,
dist/build/Control/Monad/Error/Class.o )
Control/Monad/Error/Class.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
[ 4 of 21] Compiling Control.Monad.State.Class ( Control/Monad/State/Class.hs,
dist/build/Control/Monad/State/Class.o )
Control/Monad/State/Class.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
[ 5 of 21] Compiling Control.Monad.Reader.Class (
Control/Monad/Reader/Class.hs, dist/build/Control/Monad/Reader/Class.o )
Control/Monad/Reader/Class.hs:1:0:
Warning: Module `Prelude' is
Re: [Haskell-cafe] Need Control.Monad.State
On 28 July 2010 13:17, michael rice nowg...@yahoo.com wrote:
See below. Lot's of warnings. Is the install OK? If so, can I use the same
*import*?
Yeah, the install is OK. The meaning of the warnings are:
* Warning: -fallow-undecidable-instances is deprecated: this GHC
option has changed name, but the mtl package still uses the old name.
* Warning: Module `Prelude' is deprecated: mtl doesn't specify any
bounds on the version of the base library to be used (mainly because
of historic reasons when it wasn't changing much and the Haskell
community wasn't stressing versioning as much; note that the last
version of mtl was released almost 2 years ago). Because a lot of
packages broke when GHC-6.10.4 started shipping with base-4 (along
with base-3 for compatability purposes) due to the differences in how
exceptions were handled, if there is no upper bound on the version of
base to be used then cabal-install plays it safe and uses base-3.
However, the next version of GHC (6.14, which should be coming out
later this year) will not ship with base-3, so GHC-6.12 included that
warning message for people that kept trying to use base-3 that their
code won't work with 6.14.
So yes, now you can use import Control.Monad.State.
Michael
--- On Tue, 7/27/10, Ivan Miljenovic ivan.miljeno...@gmail.com wrote:
If it isn't installed, you can use cabal-install to install it:
cabal install mtl
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
[mich...@localhost ~]$ cabal install mtl
Resolving dependencies...
Downloading mtl-1.1.0.2...
Configuring mtl-1.1.0.2...
Preprocessing library mtl-1.1.0.2...
Building mtl-1.1.0.2...
[ 1 of 21] Compiling Control.Monad.Identity ( Control/Monad/Identity.hs,
dist/build/Control/Monad/Identity.o )
Control/Monad/Cont.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Cont/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Error.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Error/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Identity.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
Control/Monad/List.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/RWS/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/RWS/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Reader.hs:2:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Reader/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/State/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/State/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
Control/Monad/Writer/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-} instead
[ 2 of 21] Compiling Control.Monad.Writer.Class (
Control/Monad/Writer/Class.hs, dist/build/Control/Monad/Writer/Class.o )
Control/Monad/Writer/Class.hs:1:0:
Warning: Module `Prelude' is deprecated:
Re: [Haskell-cafe] Need Control.Monad.State
I didn't realize the State monad wasn't part of the base install. Any
particular reason for this?
-deech
On Tue, Jul 27, 2010 at 10:24 PM, Ivan Miljenovic ivan.miljeno...@gmail.com
wrote:
On 28 July 2010 13:17, michael rice nowg...@yahoo.com wrote:
See below. Lot's of warnings. Is the install OK? If so, can I use the
same *import*?
Yeah, the install is OK. The meaning of the warnings are:
* Warning: -fallow-undecidable-instances is deprecated: this GHC
option has changed name, but the mtl package still uses the old name.
* Warning: Module `Prelude' is deprecated: mtl doesn't specify any
bounds on the version of the base library to be used (mainly because
of historic reasons when it wasn't changing much and the Haskell
community wasn't stressing versioning as much; note that the last
version of mtl was released almost 2 years ago). Because a lot of
packages broke when GHC-6.10.4 started shipping with base-4 (along
with base-3 for compatability purposes) due to the differences in how
exceptions were handled, if there is no upper bound on the version of
base to be used then cabal-install plays it safe and uses base-3.
However, the next version of GHC (6.14, which should be coming out
later this year) will not ship with base-3, so GHC-6.12 included that
warning message for people that kept trying to use base-3 that their
code won't work with 6.14.
So yes, now you can use import Control.Monad.State.
Michael
--- On Tue, 7/27/10, Ivan Miljenovic ivan.miljeno...@gmail.com wrote:
If it isn't installed, you can use cabal-install to install it:
cabal install mtl
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
[mich...@localhost ~]$ cabal install mtl
Resolving dependencies...
Downloading mtl-1.1.0.2...
Configuring mtl-1.1.0.2...
Preprocessing library mtl-1.1.0.2...
Building mtl-1.1.0.2...
[ 1 of 21] Compiling Control.Monad.Identity ( Control/Monad/Identity.hs,
dist/build/Control/Monad/Identity.o )
Control/Monad/Cont.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Cont/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Error.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Error/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Identity.hs:1:0:
Warning: Module `Prelude' is deprecated:
You are using the old package `base' version 3.x.
Future GHC versions will not support base version 3.x. You
should update your code to use the new base version 4.x.
Control/Monad/List.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/RWS/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/RWS/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Reader.hs:2:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Reader/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/State/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/State/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Writer.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Writer/Class.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Writer/Lazy.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
-XUndecidableInstances or pragma {-# LANGUAGE UndecidableInstances #-}
instead
Control/Monad/Writer/Strict.hs:1:11:
Warning: -fallow-undecidable-instances is deprecated: use
Re: [Haskell-cafe] new Cabal user question -- installing to Haskell Platform on Windows network drive?
On Tue, Jul 27, 2010 at 2:43 PM, Peter Schmitz ps.hask...@gmail.com wrote: So, by default, cabal wants to put its config and updates on C:. I looked at C:\Documents and Settings\pschmitz\Application Data\cabal\config It has various references to C:, some commented out. E.g.: remote-repo-cache: C:\Documents and Settings\pschmitz\Application Data\cabal\packages build-summary: C:\Documents and Settings\pschmitz\Application Data\cabal\logs\build.log install-dirs user -- prefix: C:\\Documents and Settings\\pschmitz\\Application Data\\cabal You can change these to whatever you want, and cabal should just start using those locations, if that helps. Given that I want to keep everything on H:, and assuming that I don't want to place the Cabal configs and updates in the Platform tree (H:\proc\tools\Haskell Platform), I would _like_ to create a dir such as H:\proc\tools\cabal to hold everything that Cabal would normally put on C:. *** I'm afraid I'm having trouble figuring out how to accomplish this. Is there (hopefully) a combination of cabal command line switches that will create a new config file over on H: for me, or must I edit the config file directly and move it to H:? There are others on this list that know cabal much better than I, but I have been working with it a bit recently, so I'll take a stab.. I don't believe you can configure *cabal* to look on H: for the cabal config, without specifying . I believe it uses the windows Application Data directory for your current user to locate the cabal config (there is a windows system (?) call that returns something akin to c:\Documents and Settings\username\Application Data\ ). You *can* change the location of your Application Data directory by hacking the windows registry, but that is likely to cause more pain than it is worth. I think you will be best served by just editing the entries in your cabal config (if that, even) unless you have a very good reason to relocate the cabal config itself. (Ok, so I think I lied a little -- iirc, there is an undocumented cabal flag that will let you specify the path to the cabal config file to use. I think it has to be the first parameter to cabal, and I think it's --cabal-config=file, but I've only used it once and I don't think it's really worth the trouble in your case. Application Data is a pretty standard place for things like this.) --Rogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Need Control.Monad.State
On 28 July 2010 14:07, aditya siram aditya.si...@gmail.com wrote: I didn't realize the State monad wasn't part of the base install. Any particular reason for this? Because there's no reason for it to be? GHC is bundled with enough libraries as it is (and with the exception of Cabal, it's not safe to upgrade any of them). However, mtl _is_ part of the Haskell Platform, so in that sense it's part of the _recommended_ base install... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Int and ByteStrings
Don Stewart wrote: wren: Hey all, Is there a library function (f :: [Int] - ByteString) such that it's prefix-preserving, and platform independent? GHC-only is fine for now. There are a bunch of functions of that type, but I need those guarantees and I'm hoping someone else has already done it. should be possible to write using Data.Binary. Definitely possible, I was just hoping it's already been done :) -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
