Re: [Haskell-cafe] Datapacker?
On Thursday 10 May 2012 04:09:33 sharon kimble wrote: > On Thursday 10 May 2012 04:01:56 you wrote: > > What is datapacker? Can you summarize the sort of problem you are having? > > https://github.com/jgoerzen/datapacker/wiki datapacker is a > tool to group files by size. It is perhaps most often used to fit a set of > files onto the minimum number of CDs or DVDs. > > I just want to check the syntax of the command before i commit it to stone > for backing up my mp3s? > > Thanks > Sharon. > > > On May 9, 2012 9:34 PM, "sharon kimble" wrote: > > > Is this the right place to ask questions about datapacker please? If > > > not, can > > > anyone tell me where is please? > > > > > > Thanks > > > Sharon. > > > -- -- A taste of linux = http://www.sharons.org.uk/taste/index.html efever = http://www.efever.blogspot.com/ efever = http://sharon04.livejournal.com/ Debian 6,0.4, Gnome 1:2.30+7, LibreOffice 3.4.6 Registered Linux user 334501 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Datapacker?
On Wed, May 9, 2012 at 10:09 PM, sharon kimble wrote: > On Thursday 10 May 2012 04:01:56 you wrote: >> What is datapacker? Can you summarize the sort of problem you are having? > > https://github.com/jgoerzen/datapacker/wiki datapacker is a tool > to group files by size. It is perhaps most often used to fit a set of files > onto > the minimum number of CDs or DVDs. > > I just want to check the syntax of the command before i commit it to stone for > backing up my mp3s? > You should probably ask the author - that link is a part of the author's personal github page. Here is some contact information: http://www.complete.org/JohnGoerzen Antoine > Thanks > Sharon. >> >> On May 9, 2012 9:34 PM, "sharon kimble" wrote: >> > Is this the right place to ask questions about datapacker please? If not, >> > can >> > anyone tell me where is please? >> > >> > Thanks >> > Sharon. >> > -- > > -- > A taste of linux = http://www.sharons.org.uk/taste/index.html > efever = http://www.efever.blogspot.com/ > efever = http://sharon04.livejournal.com/ > Debian 6,0.4, Gnome 1:2.30+7, LibreOffice 3.4.6 > Registered Linux user 334501 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Datapacker?
What is datapacker? Can you summarize the sort of problem you are having? On May 9, 2012 9:34 PM, "sharon kimble" wrote: > Is this the right place to ask questions about datapacker please? If not, > can > anyone tell me where is please? > > Thanks > Sharon. > -- > A taste of linux = http://www.sharons.org.uk/taste/index.html > efever = http://www.efever.blogspot.com/ > efever = http://sharon04.livejournal.com/ > Debian 6,0.4, Gnome 1:2.30+7, LibreOffice 3.4.6 > Registered Linux user 334501 > > ___ > 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] Datapacker?
Is this the right place to ask questions about datapacker please? If not, can anyone tell me where is please? Thanks Sharon. -- A taste of linux = http://www.sharons.org.uk/taste/index.html efever = http://www.efever.blogspot.com/ efever = http://sharon04.livejournal.com/ Debian 6,0.4, Gnome 1:2.30+7, LibreOffice 3.4.6 Registered Linux user 334501 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 226
Welcome to issue 226 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 29 to May 5, 2012. Quotes of the Week * acowley: I write the most complicated bottoms * Cale: OpenGL is the Rubik's Cube of graphics libraries. It's nearly impossible to change some things without affecting other things Top Reddit Stories * HJ — Haskell-to-JavaScript compiler (WIP) Domain: chrisdone.com, Score: 74, Comments: 23 On Reddit: [1] http://goo.gl/gP51N Original: [2] http://goo.gl/g32rz * Life Without Objects Domain: skipoleschris.blogspot.co.uk, Score: 52, Comments: 17 On Reddit: [3] http://goo.gl/LZmLC Original: [4] http://goo.gl/NLhKH * New major release of the containers package Domain: blog.johantibell.com, Score: 52, Comments: 25 On Reddit: [5] http://goo.gl/yjblJ Original: [6] http://goo.gl/DKlmd * Haskell and the World: Encodings and the Common Misuse of ByteString Domain: a-dimit.blogspot.com, Score: 50, Comments: 27 On Reddit: [7] http://goo.gl/WloCn Original: [8] http://goo.gl/oeIIW * How to write hybrid CPU/GPU programs with Haskell Domain: parfunk.blogspot.com.au, Score: 48, Comments: 3 On Reddit: [9] http://goo.gl/u9A9l Original: [10] http://goo.gl/s917R * phantom tainting with kind error messages Domain: article.gmane.org, Score: 35, Comments: 5 On Reddit: [11] http://goo.gl/V9qRd Original: [12] http://goo.gl/cx4cD * Annotated slides: Comparing Dynamic and Static Language Approaches to Web Frameworks (Rails vs Yesod) Domain: cs.kent.ac.uk, Score: 32, Comments: 11 On Reddit: [13] http://goo.gl/jE2iK Original: [14] http://goo.gl/2dIjQ * SPJ talk: Towards Haskell in the Cloud Domain: skillsmatter.com, Score: 30, Comments: 16 On Reddit: [15] http://goo.gl/fVc0e Original: [16] http://goo.gl/NMtPD * hotswap -- a simple, high level interface to plugins for hotswapping code Domain: hackage.haskell.org, Score: 29, Comments: 8 On Reddit: [17] http://goo.gl/kvhOS Original: [18] http://goo.gl/VMAe0 * Online Haskell typechecker Domain: haskellonline.org, Score: 29, Comments: 12 On Reddit: [19] http://goo.gl/uV3HY Original: [20] http://goo.gl/lSwhb Top StackOverflow Questions * Algebraically interpreting polymorphism votes: 21, answers: 5 Read on SO: [21] http://goo.gl/7krnc * Absolute value of negative zero - bug, or a part of the floating point standard? votes: 16, answers: 3 Read on SO: [22] http://goo.gl/HDpRc * how to implement doubly linked lists votes: 10, answers: 1 Read on SO: [23] http://goo.gl/hXyDM * GHC type inference for higher rank types - assigning to monotypes votes: 10, answers: 1 Read on SO: [24] http://goo.gl/TqYtX * Communication between Java and Haskell votes: 9, answers: 3 Read on SO: [25] http://goo.gl/zMYwx * Default constraint kinds are ignored votes: 9, answers: 2 Read on SO: [26] http://goo.gl/AElL4 * Scrap Your Boilerplate equivalent in Scala? votes: 7, answers: 1 Read on SO: [27] http://goo.gl/Cd7k4 * Does the chain function in underscore.js create a monad? votes: 7, answers: 1 Read on SO: [28] http://goo.gl/DUYkB * Why do Haskell list comprehensions with multiple generators treat the rightmost generator as the tightest loop? votes: 6, answers: 3 Read on SO: [29] http://goo.gl/BnndW * Haskell records, cleaner approach? votes: 6, answers: 1 Read on SO: [30] http://goo.gl/MymyL Until next time, Daniel Santa Cruz References 1. http://chrisdone.com/hj/ 2. http://www.reddit.com/r/haskell/comments/t06ej/hj_haskelltojavascript_compiler_wip/ 3. http://skipoleschris.blogspot.co.uk/2012/04/life-without-objects.html 4. http://www.reddit.com/r/haskell/comments/t1oen/life_without_objects/ 5. http://blog.johantibell.com/2012/05/new-major-release-of-containers-package.html 6. http://www.reddit.com/r/haskell/comments/t688l/new_major_release_of_the_containers_package/ 7. http://a-dimit.blogspot.com/2012/04/strings-in-haskell.html 8. http://www.reddit.com/r/haskell/comments/syo8h/haskell_and_the_world_encodings_and_the_common/ 9. http://parfunk.blogspot.com.au/2012/05/how-to-write-hybrid-cpugpu-programs.html 10. http://www.reddit.com/r/haskell/comments/t7znh/how_to_write_hybrid_cpugpu_programs_with_haskell/ 11. http://article.gmane.org/gmane.comp.lang.haskell.cafe/98103 12. http://www.reddit.com/r/haskell/comments/t6dn7/phantom_tainting_with_kind_error_messages/ 13. http://www.cs.kent.ac.uk/~nccb/rails-yesod-slides.pdf 14. http://www.reddit.com/r/haskell/comments/t1aw8/annotated_slides_comparing_dynamic_and_static/ 15. http://skillsmatter.com/podcast/home/haskell-cloud/js-4179 16. http://www.reddit.com/r/haskell/comment
Re: [Haskell-cafe] Fixed point newtype confusion
On 5/8/12 8:24 PM, Sebastien Zany wrote:
Hmm, I don't understand how that would work.
Using one of the fundep versions:
class (Functor f) => Fixpoint f x | ... where
fix :: f x -> x
unfix :: x -> f x
We'd define instances like the following:
data List a = Nil | Cons a (List a)
data PreList a b = PNil | PCons a b
deriving Functor
instance Fixpoint (PreList a) (List a) where
-- fix :: PreList a (List a) -> List a
fix PNil = Nil
fix (PCons x xs) = Cons x xs
-- unfix :: List a -> PreList a (List a)
unfix Nil = PNil
unfix (Cons x xs) = PCons x xs
Or we could do:
newtype Fix f = Fix { unFix :: f (Fix f) }
instance Fixpoint (PreList a) (Fix (PreList a)) where
-- fix :: PreList a (Fix (PreList a)) -> Fix (PreList a)
fix = Fix
-- unfix :: Fix (PreList a) -> PreList a (Fix (PreList a))
unfix = unFix
I wish I could define something like this:
class (Functor f) => Fixpoint f x | x -> f where
fix :: x -> Fix f
instance (Functor f) => Fixpoint f (forall a. f a) where
fix = id
instance (Functor f, Fixpoint f x) => Fixpoint f (f x) where
fix = Fix . fmap fix
but instances with polymorphic types aren't allowed. (Why is that?)
Well, one problem is that (forall a. f a) is not a fixed-point of f.
That is, f (forall a. f a) is not isomorphic to (forall a. f a)
Another problem is that (forall a. f a) isn't exactly of kind *. It sort
of is, but since it's quantifying over * you get into (im)predicativity
issues. For example, do we allow the following type?
Maybe (forall a. f a)
Depending on what language extensions you have on and which version of
GHC you're using, the answer could be yes or it could be no. There isn't
a "right answer" per se, it just depends on what you want the semantics
of the type system to be and what other features you want to have.
Another problem is, I don't think that means what you think it means.
Supposing we were to allow it, the expanded type of the first instance
of fix would be:
fix :: (forall a. f a) -> Fix f
Which is isomorphic to
fix :: exists a. f a -> Fix f
Which means that supposing we have some (f A) where A is some unknown
but defined type, then we can turn it into Fix f. The only way that
could be possible is if we throw away all the As that occur in the (f
A). But that's not what you mean, nor what you want.
Alternatively if I could write a function that could turn
e :: forall a. F (F (F ... (F a) ... ))
into
specialize e :: F (F (F ... (F X) ... ))
that would work too, but I don't see how that's possible.
Yeah, that'd be nice. In System F, or in Haskell Core, the "forall a. b"
is treated like a special version of the function arrow. So we have a
big lambda for type abstraction (written "/\" below), and we have type
application (written in Core with "@"). Thus we know that e is eta
equivalent to:
(/\a. e @a) :: forall a. F (F (F ... (F a) ... ))
This is just like saying that given any function f :: A -> B, it is eta
equivalent to (\(x::A). f x) :: A -> B.
So if we wanted a version of e monomorphized on a = X, then we'd just say:
e @X :: forall a. F (F (F ... (F X) ... ))
There are tricks for gaining access to the type abstraction and type
application of Core, but they're all fairly fragile as I recall.
--
Live well,
~wren
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Re: [Haskell-cafe] Handcranked install of ghc / cabal-install and warning from ghc-pkg check
or should I say cabal On Wednesday, 9 May 2012 at 21:57, Graham Berks wrote: > Is there something I have todo to tell ghc about haddock etc ? > > On Tuesday, 8 May 2012 at 19:13, Graham Berks wrote: > > > Have installed 7.4.1 ghc and 0.14.0 cabal-install and then did alex, happy > > & haddock. > > > > When I do a ghc-pkg check I get > > > > $ ghc-pkg check > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/random-1.0.1.1/html/random.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/random-1.0.1.1/html > > doesn't exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/zlib-0.5.3.3/html/zlib.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/zlib-0.5.3.3/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/HTTP-4000.2.3/html/HTTP.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/HTTP-4000.2.3/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/network-2.3.0.11/html/network.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/network-2.3.0.11/html > > doesn't exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/parsec-3.1.2/html/parsec.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/parsec-3.1.2/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/text-0.11.2.0/html/text.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/text-0.11.2.0/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/mtl-2.1/html/mtl.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/mtl-2.1/html doesn't exist > > or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/transformers-0.3.0.0/html/transformers.haddock > > doesn't exist or isn't a file > > Warning: haddock-html: > > /usr/local/Cellar/cabal-install/0.14.0/share/doc/transformers-0.3.0.0/html > > doesn't exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/haddock-2.10.0/html/haddock.haddock doesn't exist or > > isn't a file > > Warning: haddock-html: /usr/local/share/doc/haddock-2.10.0/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/xhtml-3000.2.0.5/html/xhtml.haddock doesn't exist or > > isn't a file > > Warning: haddock-html: /usr/local/share/doc/xhtml-3000.2.0.5/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/ghc-paths-0.1.0.8/html/ghc-paths.haddock doesn't exist > > or isn't a file > > Warning: haddock-html: /usr/local/share/doc/ghc-paths-0.1.0.8/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/mtl-2.1.1/html/mtl.haddock doesn't exist or isn't a > > file > > Warning: haddock-html: /usr/local/share/doc/mtl-2.1.1/html doesn't exist or > > isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/transformers-0.3.0.0/html/transformers.haddock doesn't > > exist or isn't a file > > Warning: haddock-html: /usr/local/share/doc/transformers-0.3.0.0/html > > doesn't exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/QuickCheck-2.4.2/html/QuickCheck.haddock doesn't exist > > or isn't a file > > Warning: haddock-html: /usr/local/share/doc/QuickCheck-2.4.2/html doesn't > > exist or isn't a directory > > Warning: haddock-interfaces: > > /usr/local/share/doc/random-1.0.1.1/html/random.haddock doesn't exist or > > isn't a file > > Warning: haddock-html: /usr/local/share/doc/random-1.0.1.1/html doesn't > > exist or isn't a directory > > > > > > Any suggestions to fix this ? > > > > Thanks > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Handcranked install of ghc / cabal-install and warning from ghc-pkg check
Is there something I have todo to tell ghc about haddock etc ? On Tuesday, 8 May 2012 at 19:13, Graham Berks wrote: > Have installed 7.4.1 ghc and 0.14.0 cabal-install and then did alex, happy & > haddock. > > When I do a ghc-pkg check I get > > $ ghc-pkg check > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/random-1.0.1.1/html/random.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/random-1.0.1.1/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/zlib-0.5.3.3/html/zlib.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/zlib-0.5.3.3/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/HTTP-4000.2.3/html/HTTP.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/HTTP-4000.2.3/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/network-2.3.0.11/html/network.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/network-2.3.0.11/html > doesn't exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/parsec-3.1.2/html/parsec.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/parsec-3.1.2/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/text-0.11.2.0/html/text.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/text-0.11.2.0/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/mtl-2.1/html/mtl.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/mtl-2.1/html doesn't exist > or isn't a directory > Warning: haddock-interfaces: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/transformers-0.3.0.0/html/transformers.haddock > doesn't exist or isn't a file > Warning: haddock-html: > /usr/local/Cellar/cabal-install/0.14.0/share/doc/transformers-0.3.0.0/html > doesn't exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/haddock-2.10.0/html/haddock.haddock doesn't exist or > isn't a file > Warning: haddock-html: /usr/local/share/doc/haddock-2.10.0/html doesn't exist > or isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/xhtml-3000.2.0.5/html/xhtml.haddock doesn't exist or > isn't a file > Warning: haddock-html: /usr/local/share/doc/xhtml-3000.2.0.5/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/ghc-paths-0.1.0.8/html/ghc-paths.haddock doesn't exist > or isn't a file > Warning: haddock-html: /usr/local/share/doc/ghc-paths-0.1.0.8/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: /usr/local/share/doc/mtl-2.1.1/html/mtl.haddock > doesn't exist or isn't a file > Warning: haddock-html: /usr/local/share/doc/mtl-2.1.1/html doesn't exist or > isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/transformers-0.3.0.0/html/transformers.haddock doesn't > exist or isn't a file > Warning: haddock-html: /usr/local/share/doc/transformers-0.3.0.0/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/QuickCheck-2.4.2/html/QuickCheck.haddock doesn't exist > or isn't a file > Warning: haddock-html: /usr/local/share/doc/QuickCheck-2.4.2/html doesn't > exist or isn't a directory > Warning: haddock-interfaces: > /usr/local/share/doc/random-1.0.1.1/html/random.haddock doesn't exist or > isn't a file > Warning: haddock-html: /usr/local/share/doc/random-1.0.1.1/html doesn't exist > or isn't a directory > > > Any suggestions to fix this ? > > Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Q] multiparam class undecidable types
Thanks Oleg, that was very helpful. i can work with that. read the rest of this if you are curious where your hints took me. you are right, I need to make the functional dependency explicit: | class Table t c | t -> c where | toLists :: t -> [[c]] | fromLists :: [[c]] -> t | | instance Table [[c]] c where | toLists = id | fromLists = id | | instance (Table t c, Show c) => Show t where | showsPrec p t = showParen (p > 10) $ showString "fromLists " . shows (head . head $ toLists t) this compiles, and 'show' prints the first cell of each table. i also understand now why i can't just print all of them: [[Int]] is one of the types where the instances overlap. | instance Show Int | instance Show a => Show [a] vs. | instance Table [[Int]] Int | instance (Table [[Int]] Int, Show Int) => Show [[Int]] the advanced overlap code you are referencing below is fascinating, but isn't it a different problem? i don't want to distinguish different the cases "Show c" and "Typeable c", but i want to use whatever instance of "Show c" is available to implement "Show t". i can't make your solution work for this, because one of the two overlapping instances (namely "Show a => Show [a]") is already provided by the surrounding code that i cannot outfit with the advanced overlap trick. or am i missing something here? i think what i will do is to instantiate all table types individually: | instance Show c => Show (SimpleTable c) where | showsPrec p t = showParen (p > 10) $ showString "FastTable " . | shows (toLists t) cheers, matthias On Wed, May 09, 2012 at 06:41:00AM -, o...@okmij.org wrote: > Date: 9 May 2012 06:41:00 - > From: o...@okmij.org > To: f...@etc-network.de > CC: haskell-cafe@haskell.org > Subject: Re: [Q] multiparam class undecidable types > > > > | instance (Table a c, Show c) => Show a where > > I would have thought that there is on overlap: the instance in my code > > above defines how to show a table if the cell is showable; > > No, the instance defines how to show values of any type; that type > must be an instance of Table. There is no `if' here: instances are > selected regardless of the context such as (Table a c, Show c) > above. The constraints in the context apply after the selection, not > during. > > Please see > ``Choosing a type-class instance based on the context'' > http://okmij.org/ftp/Haskell/TypeClass.html#class-based-overloading > > for the explanation and the solution to essentially the same problem. > > There are other problems with the instance: > > | instance (Table a c, Show c) => Show a where > > For example, there is no information for the type checker to determine > the type c. Presumably there could be instances > Table [[Int]] Int > Table [[Int]] Bool > So, when the a in (Table a c) is instantiated to [[Int]] > there could be two possibilities for c: Int and Bool. You can argue > that the type of the table uniquely determines the type of its > cells. You should tell the type checker of that, using functional > dependencies or associated types: > > class Table table where > type Cell table :: * > toLists :: table -> [[Cell table]] > > > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Hackathon in Munich
Dear all, this is a reminder of our local haskell Hackathon in Munich, Germany, which will be held on Saturday, the 12th of May. If you plan to join, check out the details at: http://www.haskell-munich.de/dates or contact me. We hope to see you on Saturday, Heinrich ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal issue
Have solved the issue with help from JP Moresmau. Used the command cabal install --dry-run --verbose=3 --global build wrapper And this gave enough detailed info to enable me to remove the conflict and resolve the issue. Thanks goes to JP ! On Wednesday, 9 May 2012 at 09:55, Graham Berks wrote: > Given that I have the dependant packages already installed when I do > > $ cabal install --dry-run --global buildwrapper Resolving dependencies... In > order, the following would be installed: mtl-2.1.1 (new version) > aeson-0.6.0.2 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 parsec-3.1.2 > (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 regex-base-0.93.2 (reinstall) > changes: mtl-2.0.1.0 -> 2.1.1 regex-tdfa-1.1.8 (reinstall) changes: > mtl-2.0.1.0 -> 2.1.1 buildwrapper-0.5.2 (new package) > > And that build wrapper doesn't have a defined dependency version number for > MTL > can someone tell me why cabal is trying to install a new version of MTL ? > > Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal issue
Given that I have the dependant packages already installed when I do $ cabal install --dry-run --global buildwrapper Resolving dependencies... In order, the following would be installed: mtl-2.1.1 (new version) aeson-0.6.0.2 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 parsec-3.1.2 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 regex-base-0.93.2 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 regex-tdfa-1.1.8 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1 buildwrapper-0.5.2 (new package) And that build wrapper doesn't have a defined dependency version number for MTL can someone tell me why cabal is trying to install a new version of MTL ? Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Annotaing abstract syntax trees
Hi Romildo, I had a quick look at your code. In general it seems fine, although I haven't tested it. You might want to use HLint to give you coding tips. I don't understand your remark about wanting the "type checker to produce an expression annotated with both positions and calculated types". Can't you make `exprTypeCheck` operate on `Ann (Range, ExprType) ExprF` instead of just `Ann ExprType ExprF`? Cheers, Pedro [1] http://community.haskell.org/~ndm/hlint/ On Tue, May 8, 2012 at 3:05 PM, José Romildo Malaquias wrote: > Hello. > > I am reading Martijn's MSc Thesis "Generic Selections of > Subexpressions", where one can found some discussions about annotating > abstract syntax trees (AST). > > In order to follow the discussion I wrote the attached Haskell program, > which is an interpreter for an simple typed expression language. The > Annotations package is used. > > The expression pattern is represented by a single recursive data > type. Annotations are used for positions in the input source, and also > for the type of expressions and subexpressions. > > I would like somebody to review the code and comment on it, as I am not > sure I am using the concepts right. > > Also I would like the type checker to produce an expression annotated > with both positions and calculated types. Currently it discards the > position annotations. Any sugestions on how to modify it is welcome. > > Next step is adding a new form of expression to introduce local variable > bindings. > > After that I want to start working with ASTs represented by mutually > recursive data types. Then I will need multirec... > > Romildo > ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
