Re: [Haskell-cafe] Snow Leopard Breaks GHC
If it is closed, it is fixed in the HEAD. Any ideas how to get hold of a copy of HEAD, when my Haskell compiler currently outputs rubbish? Bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Snow Leopard Breaks GHC
Here - http://hackage.haskell.org/trac/ghc/wiki/Building, but it won't help, cause you need working ghc to build ghc. D On 29/08/2009, at 6:33 PM, Thomas Davie wrote: If it is closed, it is fixed in the HEAD. Any ideas how to get hold of a copy of HEAD, when my Haskell compiler currently outputs rubbish? Bob ___ 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] Edinburgh Saturday Meetup - we are here! (Henderson's)
Dear Haskellers, Just for info, we are currently at Henderson's Cafe on Hanover St (just around the corner from the RCPE). If anybody needs to get in touch: Eric - +44 75187 28483 Dougal - +44 7814 412539 More details on the wiki if we move: http://www.haskell.org/haskellwiki/Hac7 -- Eric Kow http://www.nltg.brighton.ac.uk/home/Eric.Kow PGP Key ID: 08AC04F9 pgp9L0swITMVt.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with monadic formlets
Hello, Yeah, it seems that checkM in formlets 0.6 broken. I reported the bug to MightByte as well. - jeremy At Fri, 28 Aug 2009 12:49:08 +0100, Colin Paul Adams wrote: Colin == Colin Paul Adams co...@colina.demon.co.uk writes: Jeremy == Jeremy Shaw jer...@n-heptane.com writes: Colin apparent data corruprion is occurring. I am suspecting a Colin bug in the formlets library (I have version 0.6). Colin So I have created a slightly cut-down (no database Colin involved) complete working program. Can you see if this Colin works ok with your version of formlets: I managed to uninstall formlets-0.6 myself, and then installed 0.5 instead. After adding the necessary extra argument to runFormletState (an empty string), the test program works fine. So this seems to be a bug in formlets-0.6. -- Colin Adams Preston Lancashire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Snow Leopard Breaks GHC
Hi, If you compile with: -opta -m32 -optl -m32 Then you can get GHC to produce binaries again. WARNING: currently you cannot use this trick to build a Snow Leopard compatible GHC using the HEAD snapshot at http://www.haskell.org/ghc/dist/current/d ist/, because the most recent (20090828) does not include the relevant patch. You have to use HEAD directly, at least until the next packaged source release shows up in that directory. Once you have the source code from HEAD, you can add those flags to SRC_HC_OPTS in your mk/build.mk and it should work. Disclaimer: I haven't actually tried this yet. Cheers, Max 2009/8/29 Dmitri Sosnik dim...@gmail.com: Here - http://hackage.haskell.org/trac/ghc/wiki/Building, but it won't help, cause you need working ghc to build ghc. D On 29/08/2009, at 6:33 PM, Thomas Davie wrote: If it is closed, it is fixed in the HEAD. Any ideas how to get hold of a copy of HEAD, when my Haskell compiler currently outputs rubbish? Bob ___ 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 mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GUI library
I want to choose a GUI library for my project. Some background: I'm a beginner to functional programming and have been working through Haskell books for a few months now. I'm not just learning Haskell for s**ts and giggles; my purpose is to write music-composition-related code; in particular, I want to write a graphical musical score editor. (Why write my own editor, you may ask? Because I want to fully integrate it with computer-assisted-composition algorithms that I plan to write, also in Haskell.) I decided to use Haskell for its great features as a functional programming language. Regarding a choice of GUI library, I want these factors: - it needs to provide at a minimum a drawing surface, a place I can draw lines and insert characters, in addition to all the standard widgets and layout capabilities we have to come to expect from a GUI library. - This is a Windows application. - it needs to be non-confusing for an intermediate-beginner Haskeller. Hopefully good documentation and examples will exist on the web. - It might be nice to have advanced graphics capability such as Qt provides, things like antialiasied shapes, and a canvas with efficient refresh (refereshes only the area that was exposed, and if your canvas items are only primitives, it can do refreshes from within C++ (no need to touch your Haskell code at all). However I'm wondering if qtHaskell fits my criteria well-documented and lots of examples aimed at beginners. Thanks, Mike ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to calculate de number of digits of an integer? (was: Is logBase right?)
Uwe Hollerbach wrote: Here's my version... maybe not as elegant as some, but it seems to work. For base 2 (or 2^k), it's probably possible to make this even more efficient by just walking along the integer as stored in memory, but that difference probably won't show up until at least tens of thousands of digits. Uwe ilogb :: Integer - Integer - Integer ilogb b n | n 0 = ilogb b (- n) | n b = 0 | otherwise = (up 1) - 1 where up a = if n (b ^ a) then bin (quot a 2) a else up (2*a) bin lo hi = if (hi - lo) = 1 then hi else let av = quot (lo + hi) 2 in if n (b ^ av) then bin lo av else bin av hi We can streamline this algorithm, avoiding the repeated iterated squaring of the base that (^) does: -- numDigits b n | n 0 = 1 + numDigits b (-n) numDigits b n = 1 + fst (ilog b n) where ilog b n | n b = (0, n) | otherwise = let (e, r) = ilog (b*b) n in if r b then (2*e, r) else (2*e+1, r `div` b) It's a worthwhile optimization, as timings on n = 2^100 show: Prelude T length (show n) 301030 (0.48 secs, 17531388 bytes) Prelude T numDigits 10 n 301030 (0.10 secs, 4233728 bytes) Prelude T ilogb 10 n 301029 (1.00 secs, 43026552 bytes) (Code compiled with -O2, but the interpreted version is just as fast; the bulk of the time is spent in gmp anyway.) Regards, Bertram ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Snow Leopard Breaks GHC
Well if I build GHC on Leopard from HEAD and then copy it to Snow Leopard would that not work? Dave On Sat, Aug 29, 2009 at 1:52 AM, Dmitri Sosnik dim...@gmail.com wrote: Here - http://hackage.haskell.org/trac/ghc/wiki/Building, but it won't help, cause you need working ghc to build ghc. D On 29/08/2009, at 6:33 PM, Thomas Davie wrote: If it is closed, it is fixed in the HEAD. Any ideas how to get hold of a copy of HEAD, when my Haskell compiler currently outputs rubbish? Bob ___ 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 mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error during hlint install ?
Hi Dusan, Am I doing something wrong if I get the following error during cabal installation of hlint? Is there any way how to solve it? The problem is that version 1.15 of hscolour released recently is incompatible with 1.13 which HLint was being tested against. I've now switched over to hscolour 1.15 and released HLint 1.6.6, which does work with hscolour 1.15. This should solve your problem. I didn't spot this email as I've been busy recently and have not had a chance to read through haskell-cafe, but I did get your personal email (but replied to everyone so that everyone can see the solution). In general when emailing about my packages it's usually best to email haskell-cafe and CC me. Thanks for reporting the issue, and do let me know if the new version still doesn't work. To upgrade you should be able to do: cabal update cabal install hlint Thanks Neil I run on: Linux pc 2.6.30-ARCH #1 SMP PREEMPT Fri Jul 31 07:30:28 CEST 2009 x86_64 Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz GenuineIntel GNU/Linux The Glorious Glasgow Haskell Compilation System, version 6.10.4 Error: cabal install hlint Resolving dependencies... Configuring hlint-1.6.5... Preprocessing executables for hlint-1.6.5... Building hlint-1.6.5... [ 1 of 25] Compiling Paths_hlint ( dist/build/autogen/Paths_hlint.hs, dist/build/hlint/hlint-tmp/Paths_hlint.o ) [ 2 of 25] Compiling Parallel ( src/Parallel.hs, dist/build/hlint/hlint-tmp/Parallel.o ) [ 3 of 25] Compiling HSE.Generics ( src/HSE/Generics.hs, dist/build/hlint/hlint-tmp/HSE/Generics.o ) [ 4 of 25] Compiling HSE.NameMatch ( src/HSE/NameMatch.hs, dist/build/hlint/hlint-tmp/HSE/NameMatch.o ) [ 5 of 25] Compiling Util ( src/Util.hs, dist/build/hlint/hlint-tmp/Util.o ) [ 6 of 25] Compiling HSE.Util ( src/HSE/Util.hs, dist/build/hlint/hlint-tmp/HSE/Util.o ) [ 7 of 25] Compiling HSE.Match ( src/HSE/Match.hs, dist/build/hlint/hlint-tmp/HSE/Match.o ) [ 8 of 25] Compiling HSE.Bracket ( src/HSE/Bracket.hs, dist/build/hlint/hlint-tmp/HSE/Bracket.o ) [ 9 of 25] Compiling HSE.Evaluate ( src/HSE/Evaluate.hs, dist/build/hlint/hlint-tmp/HSE/Evaluate.o ) [10 of 25] Compiling HSE.All ( src/HSE/All.hs, dist/build/hlint/hlint-tmp/HSE/All.o ) [11 of 25] Compiling CmdLine ( src/CmdLine.hs, dist/build/hlint/hlint-tmp/CmdLine.o ) [12 of 25] Compiling Type ( src/Type.hs, dist/build/hlint/hlint-tmp/Type.o ) [13 of 25] Compiling Hint.Naming ( src/Hint/Naming.hs, dist/build/hlint/hlint-tmp/Hint/Naming.o ) [14 of 25] Compiling Hint.Bracket ( src/Hint/Bracket.hs, dist/build/hlint/hlint-tmp/Hint/Bracket.o ) [15 of 25] Compiling Hint.Lambda ( src/Hint/Lambda.hs, dist/build/hlint/hlint-tmp/Hint/Lambda.o ) [16 of 25] Compiling Hint.Monad ( src/Hint/Monad.hs, dist/build/hlint/hlint-tmp/Hint/Monad.o ) [17 of 25] Compiling Hint.ListRec ( src/Hint/ListRec.hs, dist/build/hlint/hlint-tmp/Hint/ListRec.o ) [18 of 25] Compiling Hint.List ( src/Hint/List.hs, dist/build/hlint/hlint-tmp/Hint/List.o ) [19 of 25] Compiling Hint.Match ( src/Hint/Match.hs, dist/build/hlint/hlint-tmp/Hint/Match.o ) [20 of 25] Compiling Settings ( src/Settings.hs, dist/build/hlint/hlint-tmp/Settings.o ) [21 of 25] Compiling Report ( src/Report.hs, dist/build/hlint/hlint-tmp/Report.o ) src/Report.hs:49:22: Couldn't match expected type `String' against inferred type `Bool' In the second argument of `hscolour', namely `True' In the expression: hscolour False True In the definition of `code': code = hscolour False True cabal: Error: some packages failed to install: hlint-1.6.5 failed during the building phase. The exception was: exit: ExitFailure 1 Regards Dušan P.S. Registered packages: Cabal-1.6.0.3, HUnit-1.2.0.3, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.1, base-4.1.0.0, bytestring-0.9.1.4, containers-0.2.0.1, cpphs-1.8, directory-1.0.0.3, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), extensible-exceptions-0.1.1.0, filepath-1.1.0.2, (ghc-6.10.4), ghc-prim-0.1.0.0, haddock-2.4.2, haskell-src-1.0.1.3, haskell-src-exts-1.0.1, haskell98-1.0.1.0, hpc-0.5.0.3, hscolour-1.15, html-1.0.1.2, integer-0.1.0.1, mtl-1.1.0.2, network-2.2.1.2, old-locale-1.0.0.1, old-time-1.0.0.2, packedstring-0.1.0.1, parallel-1.1.0.1, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.1, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.1, template-haskell-2.3.0.1, time-1.1.4, uniplate-1.2.0.3, unix-2.3.2.0, xhtml-3000.2.0.1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org
Re: [Haskell-cafe] GUI library
Hi Jean-Denis, Thanks for the information. Do you know how WxHaskell fits my needs? For example, does it have good docs and examples for a beginner? Does it have the ability to draw lines and characters on a surface? Does it have a type of canvas which usually refers to an optimized drawing surface? Thanks, Mike Jean-Denis Koeck wrote: I began writing a commercial app with a GUI using Gtk2hs, but it looked ugly on Windows. I'm switching to WxHaskell. 2009/8/29 Michael Mossey m...@alumni.caltech.edu mailto:m...@alumni.caltech.edu I want to choose a GUI library for my project. Some background: I'm a beginner to functional programming and have been working through Haskell books for a few months now. I'm not just learning Haskell for s**ts and giggles; my purpose is to write music-composition-related code; in particular, I want to write a graphical musical score editor. (Why write my own editor, you may ask? Because I want to fully integrate it with computer-assisted-composition algorithms that I plan to write, also in Haskell.) I decided to use Haskell for its great features as a functional programming language. Regarding a choice of GUI library, I want these factors: - it needs to provide at a minimum a drawing surface, a place I can draw lines and insert characters, in addition to all the standard widgets and layout capabilities we have to come to expect from a GUI library. - This is a Windows application. - it needs to be non-confusing for an intermediate-beginner Haskeller. Hopefully good documentation and examples will exist on the web. - It might be nice to have advanced graphics capability such as Qt provides, things like antialiasied shapes, and a canvas with efficient refresh (refereshes only the area that was exposed, and if your canvas items are only primitives, it can do refreshes from within C++ (no need to touch your Haskell code at all). However I'm wondering if qtHaskell fits my criteria well-documented and lots of examples aimed at beginners. Thanks, Mike ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org mailto: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] GUI library
On Sat, Aug 29, 2009 at 8:03 AM, Michael Mosseym...@alumni.caltech.edu wrote: I want to choose a GUI library for my project. Some background: I'm a beginner to functional programming and have been working through Haskell books for a few months now. I'm not just learning Haskell for s**ts and giggles; my purpose is to write music-composition-related code; in particular, I want to write a graphical musical score editor. (Why write my own editor, you may ask? Because I want to fully integrate it with computer-assisted-composition algorithms that I plan to write, also in Haskell.) I decided to use Haskell for its great features as a functional programming language. Regarding a choice of GUI library, I want these factors: - it needs to provide at a minimum a drawing surface, a place I can draw lines and insert characters, in addition to all the standard widgets and layout capabilities we have to come to expect from a GUI library. - This is a Windows application. - it needs to be non-confusing for an intermediate-beginner Haskeller. Hopefully good documentation and examples will exist on the web. - It might be nice to have advanced graphics capability such as Qt provides, things like antialiasied shapes, and a canvas with efficient refresh (refereshes only the area that was exposed, and if your canvas items are only primitives, it can do refreshes from within C++ (no need to touch your Haskell code at all). However I'm wondering if qtHaskell fits my criteria well-documented and lots of examples aimed at beginners. I've never used it myself, but if you're going to be drawing a lot perhaps cairo is right for you? http://cairographics.org/hscairo/ I suspect you'll have to be self-taught here. Gtk2Hs and WxHaskell are probably the most mature gui libs for Haskell. Yet with either one you may end up dropping down into GDI/GDI+ or opengl on windows to get what you want. GDI/GDI+ is confusing in any language, but good books/resources do exist. So perhaps the trick here is to translate good documentation from other languages/sources into Haskell examples. You could do this as a warm up exercise before starting on your music editor. Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Composition of n-arity functions
Hello,
In the levmar binding[1][2] me and my brother are working on, I need a
function composition operator that is overloaded to work on functions
of any arity. Basically its type needs to be something like the
following:
(.*) :: (b - c) - NFunction n a b - NFunction n a c
where 'NFunction n a b' represents the function 'a_0 - a_1 - ... - a_n - b'
I have written the following implementation:
(my question to this list is below)
-- Begin ---
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleContexts #-}
module ComposeN where
-- Type-level naturals (from an idea by Ryan Ingram)
data Z = Z
newtype S n = S n
type N0 = Z
type N1 = S N0
type N2 = S N1
type N3 = S N2
class Nat n where
caseNat :: forall r.
n
- (n ~ Z = r)
- (forall p. (n ~ S p, Nat p) = p - r)
- r
instance Nat Z where
caseNat _ z _ = z
instance Nat n = Nat (S n) where
caseNat (S n) _ s = s n
induction :: forall p n. Nat n
= n
- p Z
- (forall x. Nat x = p x - p (S x))
- p n
induction n z s = caseNat n isZ isS
where
isZ :: n ~ Z = p n
isZ = z
isS :: forall x. (n ~ S x, Nat x) = x - p n
isS x = s (induction x z s)
newtype Witness x = Witness { unWitness :: x }
witnessNat :: forall n. Nat n = n
witnessNat = theWitness
where
theWitness = unWitness $ induction (undefined `asTypeOf` theWitness)
(Witness Z)
(Witness . S . unWitness)
-- N-arity functions
-- | A @NFunction n a b@ is a function which takes @n@ arguments of
-- type @a@ and returns a @b...@.
-- For example: NFunction (S (S (S Z))) a b ~ (a - a - a - b)
type family NFunction n a b :: *
type instance NFunction Z a b = b
type instance NFunction (S n) a b = a - NFunction n a b
-- | @f .* g@ composes @f@ with the /n/-arity function @g...@.
(.*) :: forall n a b c. (ComposeN n) = (b - c) - NFunction n a b -
NFunction n a c
(.*) = compose (witnessNat :: n) (undefined :: a)
infixr 9 .* -- same as .
class Nat n = ComposeN n where
compose :: forall a b c. n - a -
(b - c) - NFunction n a b - NFunction n a c
-- Note that the 'n' and 'a' arguments to 'compose' are needed so that the type
-- checker has enough information to select the right 'compose' instance.
instance ComposeN Z where
compose Z _ = ($)
instance ComposeN n = ComposeN (S n) where
compose (S n) (_ :: a) f g = compose n (undefined :: a) f . g
-- Test
foo :: NFunction N3 Integer Integer
foo x y z = x + y + z
bar :: Integer - Integer
bar k = k - 1
test1 = compose (witnessNat :: N3)
(undefined :: Integer)
bar foo 1 2 3
test2 = (bar .* foo) 1 2 3
-- The End -
The problem is test1 type checks and evaluates to 5 as expected but
test2 gives the following type error:
Couldn't match expected type `NFunction n a Integer'
against inferred type `Integer - Integer - Integer - Integer'
In the second argument of `(.*)', namely `foo'
However if I ask ghci to infer the type of (bar .* foo) I get:
*ComposeN:t (bar .* foo)
(bar .* foo)
:: (Integer - Integer - Integer - Integer
~
NFunction n a Integer,
ComposeN n) =
NFunction n a Integer
Here we see that the context contains the type equality:
(Integer - Integer - Integer - Integer ~ NFunction n a Integer
So why is ghci unable to match the expected type `NFunction n a Integer'
against the inferred type `Integer - Integer - Integer - Integer'
while the context contains just this equality?
regards,
Bas
[1] http://code.haskell.org/~basvandijk/code/bindings-levmar/
[2] http://code.haskell.org/~basvandijk/code/levmar/
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Re: [Haskell-cafe] Composition of n-arity functions
As far as I can tell, it's because the NFunction type family isn't (at
least from GHC's point of view) invertible. Data families are
injective, but type families need not be, so it's quite fine for you
to write something like
type instance TypeFunction A = Q
type instance TypeFunction B = Q
Now if you try to say that TypeFunction n should unify with Q, what
should n be? There's the same issue with NFunction, in that it knows
how to make an n-ary function if you provide a type-level natural as a
parameter, but given an n-ary function, it doesn't know how to get the
type-level natural that corresponds to it back.
I don't really know of a solution to this, but it may be possible to
write an inverse type family to get the arity back. Not sure how
you'd tell GHC though. It'd be cool if in future we could have some
sort of annotation to declare that our type functions are injective,
without explicitly going to data families.
Hope this helps (and that I'm not completely wrong)!
Dan
On Sat, Aug 29, 2009 at 2:03 PM, Bas van Dijkv.dijk@gmail.com wrote:
Hello,
In the levmar binding[1][2] me and my brother are working on, I need a
function composition operator that is overloaded to work on functions
of any arity. Basically its type needs to be something like the
following:
(.*) :: (b - c) - NFunction n a b - NFunction n a c
where 'NFunction n a b' represents the function 'a_0 - a_1 - ... - a_n -
b'
I have written the following implementation:
(my question to this list is below)
-- Begin
---
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE FlexibleContexts #-}
module ComposeN where
-- Type-level naturals (from an idea by Ryan Ingram)
data Z = Z
newtype S n = S n
type N0 = Z
type N1 = S N0
type N2 = S N1
type N3 = S N2
class Nat n where
caseNat :: forall r.
n
- (n ~ Z = r)
- (forall p. (n ~ S p, Nat p) = p - r)
- r
instance Nat Z where
caseNat _ z _ = z
instance Nat n = Nat (S n) where
caseNat (S n) _ s = s n
induction :: forall p n. Nat n
= n
- p Z
- (forall x. Nat x = p x - p (S x))
- p n
induction n z s = caseNat n isZ isS
where
isZ :: n ~ Z = p n
isZ = z
isS :: forall x. (n ~ S x, Nat x) = x - p n
isS x = s (induction x z s)
newtype Witness x = Witness { unWitness :: x }
witnessNat :: forall n. Nat n = n
witnessNat = theWitness
where
theWitness = unWitness $ induction (undefined `asTypeOf` theWitness)
(Witness Z)
(Witness . S . unWitness)
-- N-arity functions
-- | A @NFunction n a b@ is a function which takes @n@ arguments of
-- type @a@ and returns a @b...@.
-- For example: NFunction (S (S (S Z))) a b ~ (a - a - a - b)
type family NFunction n a b :: *
type instance NFunction Z a b = b
type instance NFunction (S n) a b = a - NFunction n a b
-- | @f .* g@ composes @f@ with the /n/-arity function @g...@.
(.*) :: forall n a b c. (ComposeN n) = (b - c) - NFunction n a b -
NFunction n a c
(.*) = compose (witnessNat :: n) (undefined :: a)
infixr 9 .* -- same as .
class Nat n = ComposeN n where
compose :: forall a b c. n - a -
(b - c) - NFunction n a b - NFunction n a c
-- Note that the 'n' and 'a' arguments to 'compose' are needed so that the
type
-- checker has enough information to select the right 'compose' instance.
instance ComposeN Z where
compose Z _ = ($)
instance ComposeN n = ComposeN (S n) where
compose (S n) (_ :: a) f g = compose n (undefined :: a) f . g
-- Test
foo :: NFunction N3 Integer Integer
foo x y z = x + y + z
bar :: Integer - Integer
bar k = k - 1
test1 = compose (witnessNat :: N3)
(undefined :: Integer)
bar foo 1 2 3
test2 = (bar .* foo) 1 2 3
-- The End
-
The problem is test1 type checks and evaluates to 5 as expected but
test2 gives the following type error:
Couldn't match expected type `NFunction n a Integer'
against inferred type `Integer - Integer - Integer - Integer'
In the second argument of `(.*)', namely `foo'
However if I ask ghci to infer the type of (bar .* foo) I get:
*ComposeN:t (bar .* foo)
(bar .* foo)
Re: [Haskell-cafe] Error during hlint install ?
Yes, it works fine, now. Thank you! Dušan Neil Mitchell wrote: Hi Dusan, Am I doing something wrong if I get the following error during cabal installation of hlint? Is there any way how to solve it? The problem is that version 1.15 of hscolour released recently is incompatible with 1.13 which HLint was being tested against. I've now switched over to hscolour 1.15 and released HLint 1.6.6, which does work with hscolour 1.15. This should solve your problem. I didn't spot this email as I've been busy recently and have not had a chance to read through haskell-cafe, but I did get your personal email (but replied to everyone so that everyone can see the solution). In general when emailing about my packages it's usually best to email haskell-cafe and CC me. Thanks for reporting the issue, and do let me know if the new version still doesn't work. To upgrade you should be able to do: cabal update cabal install hlint Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with monadic formlets
At Sat, 29 Aug 2009 15:46:42 +0100,
Chris Eidhof (formlets) wrote:
Confirmed. checkM is broken, thanks for noticing! I'll have a look
into it, I'm not sure whether it can be fixed. I was thinking of
removing all the monadic stuff from the formlets. I think this will
make for a much cleaner interface, monadic checking can then be done
afterwards.
I am still a fan of (and use) this version of Form:
newtype Form xml m a = Form { deform :: Env - State FormState (Collector (m
(Failing a)), xml, FormContentType) }
not sure how I would feel about the removal of 'm' from the
Collector. But 'xml' is nicer for me than 'm xml' because my collector
and xml generator are often in different monads. I can, of course make
them be in the same monad if I want:
type MyForm a = Form (IO XML) IO a
but I also have the option of just doing:
type MyForm a = Form (IO XML) IO a
or:
type MyForm a = Form (HSP XML) IO a
At present, I actually have my collector do all the validation and
update the database. As a use case, let's assume that the form is
creating a new user account. One possible error would be using a
username that is already in use. Doing that check requires a database
query. In fact, it seems best if it does a database update, so that
there is no race condition between checking if the name is in use, and
actually attempting to create the account with that username.
If you remove the ability to do IO in the collector, then I believe I
would need to:
1. run the collector to do the pure part of the validation.
2. if the pure part succeeds, use the returned value to do the impure
validation
3. if that fails, then redisplay the form using the same environment
that I used for #1, but passing in the impure validation errors.
One potential drawback that I see with this is that it may make it
difficult to the pass the error messages back to the specific formlet
element that failed so that you can display the errors in-line.
[Note: the following discussion reflects the pre-0.6 design].
Currently the environment we pass in is something like:
type Env = [(String, Either String File)]
The first component of the tuple is the name of the element. aka,
input0, input1, etc.
I would propose that we also pass in a Failures argument:
type Failures = [(String, ErrorMsg)]
where the first component of the tuple is the name of the element
(input0, intpu1, etc) and the second element contains ErrorMsg.
or perhaps modify Env to:
type Env = [(String, (Maybe ErrorMsg, Either String File)]
We would need to modify the Failing data type to:
data Failing a = Failure [(String, ErrorMsg)] | Success a
so that Failures would contain their location.
Not all errors correspond to a specific form element. Let's say that
you have 3 drop-down boxes that combine together to form a date
selector. You want to validate the result of all three combined to
make sure they picked a valid date, and if it is invalid, you produce
an error message for that group, not a specific element. The problem
then is that there is no 'location' that corresponds to that group, so
what do you put in the Failure tuple?
I think you can use freshName to generate an extra 'virtual' name that
corresponds to the group as a whole.
I have been meaning to prototype this in the near future and see if it
actually works. I'll try to get something worked up in the next two
weeks (my sister is getting married next week, so my schedule is
pretty full).
- jeremy
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Re: [Haskell-cafe] How to calculate the number of digits of an integer? (was: Is logBase right?)
Ouch! That is indeed an improvement... I don't recall all the details of this codelet, but I think I got the seed off the net somewhere (perhaps this list?), and it might well have been better originally. So, brightly brightly and with beauty, I probably executed a verschlimmbesserung. After a year and a half, I find I still have almost no intuition about performance issues in haskell... guess I have to practice more. Uwe On 8/29/09, Bertram Felgenhauer bertram.felgenha...@googlemail.com wrote: Uwe Hollerbach wrote: Here's my version... maybe not as elegant as some, but it seems to work. For base 2 (or 2^k), it's probably possible to make this even more efficient by just walking along the integer as stored in memory, but that difference probably won't show up until at least tens of thousands of digits. Uwe ilogb :: Integer - Integer - Integer ilogb b n | n 0 = ilogb b (- n) | n b = 0 | otherwise = (up 1) - 1 where up a = if n (b ^ a) then bin (quot a 2) a else up (2*a) bin lo hi = if (hi - lo) = 1 then hi else let av = quot (lo + hi) 2 in if n (b ^ av) then bin lo av else bin av hi We can streamline this algorithm, avoiding the repeated iterated squaring of the base that (^) does: -- numDigits b n | n 0 = 1 + numDigits b (-n) numDigits b n = 1 + fst (ilog b n) where ilog b n | n b = (0, n) | otherwise = let (e, r) = ilog (b*b) n in if r b then (2*e, r) else (2*e+1, r `div` b) It's a worthwhile optimization, as timings on n = 2^100 show: Prelude T length (show n) 301030 (0.48 secs, 17531388 bytes) Prelude T numDigits 10 n 301030 (0.10 secs, 4233728 bytes) Prelude T ilogb 10 n 301029 (1.00 secs, 43026552 bytes) (Code compiled with -O2, but the interpreted version is just as fast; the bulk of the time is spent in gmp anyway.) Regards, Bertram ___ 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] Hackage rankings : August 2009
Monthly statistics on the most popular Haskell applications and libraries on Hackage. August 2009 edition now up: http://donsbot.wordpress.com/2009/08/29/haskell-popularity-rankings-september-2009/ -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to calculate de number of digits of an integer?
Bulat Ziganshin schrieb: Hello Henning, Tuesday, August 25, 2009, 7:01:24 PM, you wrote: I hope that 'show' will not need quadratic time but will employ a more efficient algorithm yes, you are right I thought a little about it. If I had to implement that in GMP it could be done quite fast in many cases: Count the number of bits, say it is 'k' and multiply with logBase 10 2. If 2^k and 2^(k+1)-1 have the same number of decimal digits, we are done. Otherwise we have to process some of the most significant bits. If the number is between n*2^k and (n+1)*2^k-1 and both bounds have the same number of decimal digits (logBase 10 n + k * logBase 10 2), we are also done. Only for numbers close to powers of 10 we have to process the whole integer. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GUI library
Jason Dagit wrote: I've never used it myself, but if you're going to be drawing a lot perhaps cairo is right for you? http://cairographics.org/hscairo/ I suspect you'll have to be self-taught here. Gtk2Hs and WxHaskell are probably the most mature gui libs for Haskell. Yet with either one you may end up dropping down into GDI/GDI+ or opengl on windows to get what you want. GDI/GDI+ is confusing in any language, but good books/resources do exist. So perhaps the trick here is to translate good documentation from other languages/sources into Haskell examples. You could do this as a warm up exercise before starting on your music editor. Jason Thanks, Jason. My drawing needs are pretty rudimentary. A music editor doesn't need much more than the ability to draw lines and characters. A nice addition would be antialiased curves such as Qt offers but that is optional. A so-called canvas sometimes offers optimized drawing updates, so the editor doesn't have to redraw the entire page if one portion of it changes. That is not strictly necessary, and in fact it wouldn't be hard to implement a bit of that functionality myself. -Mike ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to calculate de number of digits of an integer? (was: Is logBase right?)
I have a version of this inside of the monoid library buried in the Data.Ring.Semi.BitSet module: http://comonad.com/haskell/monoids/dist/doc/html/monoids/src/Data-Ring-Semi-BitSet.html#hwm http://comonad.com/haskell/monoids/dist/doc/html/monoids/src/Data-Ring-Semi-BitSet.html#hwmTo do any better by walking the raw Integer internals you need to know the 'finger' size for the GMP for your platform, which isn't possible to do portably. -Edward Kmett On Wed, Aug 26, 2009 at 10:42 AM, Uwe Hollerbach uhollerb...@gmail.comwrote: Here's my version... maybe not as elegant as some, but it seems to work. For base 2 (or 2^k), it's probably possible to make this even more efficient by just walking along the integer as stored in memory, but that difference probably won't show up until at least tens of thousands of digits. Uwe ilogb :: Integer - Integer - Integer ilogb b n | n 0 = ilogb b (- n) | n b = 0 | otherwise = (up 1) - 1 where up a = if n (b ^ a) then bin (quot a 2) a else up (2*a) bin lo hi = if (hi - lo) = 1 then hi else let av = quot (lo + hi) 2 in if n (b ^ av) then bin lo av else bin av hi numDigits n = 1 + ilogb 10 n [fire up ghci, load, etc] *Main numDigits (10^1500 - 1) 1500 *Main numDigits (10^1500) 1501 ___ 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] How to calculate de number of digits of an integer? (was: Is logBase right?)
Although this isn't a very general approach, I just submitted a patch to GHC (not yet merged) with a gmp binding to mpz_sizeinbase, which would allow for very quick computation of number of digits in any base. On Sat, Aug 29, 2009 at 9:12 PM, Edward Kmettekm...@gmail.com wrote: I have a version of this inside of the monoid library buried in the Data.Ring.Semi.BitSet module: http://comonad.com/haskell/monoids/dist/doc/html/monoids/src/Data-Ring-Semi-BitSet.html#hwm To do any better by walking the raw Integer internals you need to know the 'finger' size for the GMP for your platform, which isn't possible to do portably. -Edward Kmett On Wed, Aug 26, 2009 at 10:42 AM, Uwe Hollerbach uhollerb...@gmail.com wrote: Here's my version... maybe not as elegant as some, but it seems to work. For base 2 (or 2^k), it's probably possible to make this even more efficient by just walking along the integer as stored in memory, but that difference probably won't show up until at least tens of thousands of digits. Uwe ilogb :: Integer - Integer - Integer ilogb b n | n 0 = ilogb b (- n) | n b = 0 | otherwise = (up 1) - 1 where up a = if n (b ^ a) then bin (quot a 2) a else up (2*a) bin lo hi = if (hi - lo) = 1 then hi else let av = quot (lo + hi) 2 in if n (b ^ av) then bin lo av else bin av hi numDigits n = 1 + ilogb 10 n [fire up ghci, load, etc] *Main numDigits (10^1500 - 1) 1500 *Main numDigits (10^1500) 1501 ___ 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 mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
