Re: [Haskell-cafe] Wrong kind when attempting to build a monad for a circular list of functions
On Thu, Feb 28, 2008 at 8:28 AM, Aaron Altman [EMAIL PROTECTED] wrote: I am working on an AI agent that will perform a finite series of actions before starting the sequence over again. I figured a circular list of functions that shifts as you apply them would be the way to do it... I think a better representation of a finite series of actions is a 'Monad m = [m a]' because your AI agent will likely do some side effects when it's executing. Then if you also want to thread some state through the actions you should have a 'Monad m = [a - m a]': (Another idea is to use MonadState) import Control.Monad walk :: (Monad m) = [a - m a] - a - m a walk = foldr (=) return always :: (Monad m) = (a - m a) - a - m b always f z = f z = always f ai :: (Monad m) = a - [a - m a] - m a ai z f = always (walk f) z example = ai 0 [ \x - print x return x , \x - if x 10 then fail the end else return (x+1) ] regards, Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wrong kind when attempting to build a monad for a circular list of functions
On Thu, Feb 28, 2008 at 4:28 AM, Aaron Altman [EMAIL PROTECTED] wrote: runActionAndIterate :: [a - a] - a - (a, [a - a]) runActionAndIterate (currentAction:actionList) actionInput = (currentAction actionInput, concat [actionList, [currentAction]]) shiftActionList :: [a - a] - [a - a] shiftActionList (currentHead:rest) = concat [rest, [currentHead]] As a side note, it's not good to recreate the list (using 'concat') for every item as it is an O(n) operation. Bas van Dijk's 'always' (also called 'forever'[1]) is an option, but you can also create a circular list using the simple function 'cycle'[2] and your functions above would become runActionAndIterate (currentAction:actionList) actionInput = (currentAction actionInput, actionList) shiftActionList = tail [1] http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Monad.html#v%3Aforever [2] http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3Acycle -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wrong kind when attempting to build a monad for a circular list of functions
On Thu, Feb 28, 2008 at 8:15 AM, Roel van Dijk [EMAIL PROTECTED] wrote: I'm nitpicking but, Not a nitpick, a great difference =). As someone else already said on this list, it's not good to answer e-mails in the early morning heh. Thanks, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wrong kind when attempting to build a monad for a circular list of functions
I'm nitpicking but, On Thu, Feb 28, 2008 at 11:44 AM, Felipe Lessa [EMAIL PROTECTED] wrote: Bas van Dijk's 'always' (also called 'forever'[1]) forever a = a forever a always f z = f z = always f Forever doesn't pass the result of the action to its recursive call, always does. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wrong kind when attempting to build a monad for a circular list of functions
On Thu, Feb 28, 2008 at 7:44 AM, Felipe Lessa [EMAIL PROTECTED] wrote: Bas van Dijk's 'always' (also called 'forever'[1]) Sorry, of course always' :: Monad m = (a - m a) - (a - m ()) forever :: Monad m = (m a) - (m ()) are of different types and so are different functions. -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal errors
Hi I installed ghc 6.8 from source and I've been installing packages from hackage. I'm not sure when the problem started, but I've been getting this error trying to install any cabal package.. accept apparently, Cabal itself. Setup.hs:2:0: Warning: Deprecated use of `defaultUserHooks' (imported from Distribution.Simple): Use simpleUserHooks or autoconfUserHooks Setup: /usr/local/lib/Cabal-1.3.6/ghc-6.8.2.20080225/HSCabal-1.3.6.o: unknown symbol `directoryzm1zi0zi0zi0_SystemziDirectory_a9_closure' Setup: exception :: GhcException Any ideas? -- -kb ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bay Area talk tomorrow, on concurrent/parallel Haskell
Hello, I wish I could be there, but I'm in Kentucky. ;) It would be great if someone could have this talk recorded and posted on youtube, or something similar. Thank you. __ Donnie On 2/27/08, Bryan O'Sullivan [EMAIL PROTECTED] wrote: Satnam Singh of Microsoft Research will be speaking about concurrent and parallel programming at Stanford tomorrow. Details here: http://www.realworldhaskell.org/blog/2008/02/28/stanford-haskell-talk-2008-02-28/ b ___ 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] Bay Area talk tomorrow, on concurrent/parallel Haskell
At 13:23 28/02/2008, you wrote: Hello, I wish I could be there, but I'm in Kentucky. ;) It would be great if someone could have this talk recorded and posted on youtube, or something similar. Thank you. Now, there's an idea which could be extended to all Haskell related gatherings. __ Donnie On 2/27/08, Bryan O'Sullivan mailto:[EMAIL PROTECTED][EMAIL PROTECTED] wrote: Satnam Singh of Microsoft Research will be speaking about concurrent and parallel programming at Stanford tomorrow. Details here: http://www.realworldhaskell.org/blog/2008/02/28/stanford-haskell-talk-2008-02-28/http://www.realworldhaskell.org/blog/2008/02/28/stanford-haskell-talk-2008-02-28/ b ___ Haskell-Cafe mailing list mailto:Haskell-Cafe@haskell.orgHaskell-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] ANNOUNCE: parameterized-data 0.1 - Parameterized data library implementing lightweight dependent types
This library provides an implementation of parameterized types using type-level computations to implement the type parameters and emulate dependent types. Right now only fixed-sized vectors are provided (based on Oleg's Number-parameterized types [1] and Frederik Eaton's Vectro library [2]) HackageDB page: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/parameterized-data-0.1 Darcs repository: http://code.haskell.org/parameterized-data/ Again, big thanks to Oleg and Wolfgang for their help and suggestions. [1] http://okmij.org/ftp/Haskell/number-parameterized-types.html [2] http://ofb.net/~frederik/vectro/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] to stimulate discussion concerning where Haskell is going .. ...
1) Berkeley consternation about the inability of current concurrency to keep up with multicor developments 1) http://www.eetimes.com/news/latest/showArticle.jhtml;jsessionid=CWDB5YTIKPC4QQSNDLPSKH0CJUNN2JVN?articleID=206801376pgno=2printable=true http://www.eetimes.com/news/latest/showArticle.jhtml;?articleID=206801229 IMO a gauntlet has been thrown down to the Haskell world here. 2) Sun Microsystem's planned support of hardware transactional memory http://www.theregister.co.uk/2007/08/21/sun_transactional_memory_rock/ I have fished around and collected some Sun papers and slides. If any anybody wants I can post the URLs or send to the interested Regards, Vasys ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] to stimulate discussion concerning where Haskell is going .. ...
Hello Vasys, I am quite interested in concurrency and Haskell. I appreciate your effort, and I would like the URLs, if you don't mind. Can you elaborate on your statement IMO a gauntlet has been thrown down to the Haskell world here.? Are you implying that this is an opportunity for Haskell and concurrency? Or, that Haskell is going to be passed by? Thank you. __ Donnie On 2/28/08, Galchin Vasili [EMAIL PROTECTED] wrote: 1) Berkeley consternation about the inability of current concurrency to keep up with multicor developments 1) http://www.eetimes.com/news/latest/showArticle.jhtml;jsessionid=CWDB5YTIKPC4QQSNDLPSKH0CJUNN2JVN?articleID=206801376pgno=2printable=true http://www.eetimes.com/news/latest/showArticle.jhtml;?articleID=206801229 IMO a gauntlet has been thrown down to the Haskell world here. 2) Sun Microsystem's planned support of hardware transactional memory http://www.theregister.co.uk/2007/08/21/sun_transactional_memory_rock/ I have fished around and collected some Sun papers and slides. If any anybody wants I can post the URLs or send to the interested Regards, Vasys ___ 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] ArrowChoice for simulation arrow (Sim)
Hi, In John Hughes\' paper \Programming with arrows\ [1] Section 5, the simulation arrow is defined (Sim). All the examples went well. However, when I want to use it beyond circuit simulation and I added a \if-then-else\ line, GHC is asking to define ArrowChoice for Sim. Does anybody have the ArrowChoice definition for Sim ? Thanks, Steve [1] http://www.cs.chalmers.se/~rjmh/afp-arrows.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Hoogle 3.1
I have a question about the ranking algorithm of Hoogle 3.1: The top match of hoogle (a - b) - b is the inexact match Control.Monad.State.Class.gets :: MonadState s m = (s - a) - m a (which cannot be made to unify with (a - b) - b) instead of Control.Monad.Cont.runCont (undefined :: Cont r a) :: (a - r) - r which does. I would have thought all exact matches would come first (after considering all partial applications), especially as the increase in complexity is at most a small constant factor (~ 2 or 3) for considering all possible partial applications (type tails) of known library functions. Dan Neil Mitchell wrote: Hi, I am pleased to announce Hoogle 3.1. Hoogle is a search engine for Haskell functions, that allows the user to search by name or approximate type signature. Hoogle can be used without installing anything, by simply visiting the online interface, or can be installed locally. * Online interface: http://www.haskell.org/hoogle/ * Cabal release: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hoogle-3.1 The Cabal release contains a command line version of the Hoogle tool, which you can install with the standard Cabal commands. Hoogle 3.1 has a number of new features. Command line version: * A proper cabal release, including proper installing of the search database. * cabal-install compatible * No longer requires haskell-source-extensions (trhsx) to be installed Web interface: * Better entity escaping in some bits of the web interface * Keyword links work again * Lambdabot suggestions work * Update to the most recent version of base * Security fixes, specifically possible code injection bugs (http://en.wikipedia.org/wiki/Code_injection) - none of which were ever exploited, or could have been exploited (as far as I can tell) I intend to write a more detailed account of the security fixes in a blog post, which will be available from http://planet.haskell.org/ . Running a custom version of the web interface is not really supported, but if you are, please upgrade to the latest darcs version. There are still several known bugs in the Hoogle 3.1 release, but these are more difficult to fix, and will probably be solved in a forthcoming Hoogle 4.0. Thanks Neil ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANN: Hoogle 3.1
Hi The top match of hoogle (a - b) - b is the inexact match Control.Monad.State.Class.gets :: MonadState s m = (s - a) - m a (which cannot be made to unify with (a - b) - b) instead of Control.Monad.Cont.runCont (undefined :: Cont r a) :: (a - r) - r which does. What if the type of gets was :: (s - a) - m a? Would you then think it was the right choice of ordering? In runCont you are effectively deleting an argument to get equality, in gets you are simply unifying a and m a. Since m a is just wrapped in a container (monad in this case), its entirely feasible the person wanted the monadic version. The reason Hoogle sees gets without the type class is because MonadState is a multi-parameter type class, and hence not Haskell 98. Hoogle simply ignores all MPTC's while doing matching. This will be fixed in Hoogle 4. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Error I haven't seen before
I'm getting this error when I try to render the text contained in a record structure in the Protein module. Does this mean that the thunk that could calculate go_terms is being evaluated for the first time in the program? go_terms is calculated by a Data.Map.! lookup operation. Main: No match in record selector Protein.go_terms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: Sessions 2008 2 28 - RFC
Hi, So for those of you that watch the hackage what's-new page, you will probably be aware of this. For the last few months, there's been significant work on my implementation of Session Types in Haskell.[0] The reason for this particular announcement is that it should now be at a point where functionality is verging on useful. There are a few things that are still missing which should appear over the next few weeks but if you're at all interested in message-passing as a tool in the box for dealing with concurrency, I'd love to know what you think. To that end, I would *not* encourage you to try to look at the implementation too closely as you may suddenly discover a powerful urge to stick knives in your eyes and/or eat your computer. However, the Tests.hs[1] file should give you a good idea of the kinds of things that are possible and they do cover all the functionality currently implemented. Note that ghci may well take about 5 mins to type check Tests.hs. Or longer if you're still running a BBC B Micro. I would almost certainly not advise anyone to look at the haddock[2]. I really can't quite believe how horrible the type sigs end up looking under haddock. Some of my comments may almost pass the barrier of being useful. Nicely formatted type sigs exist in the source. If however, you are as mad as I, and enjoy pushing the GHC type system to the limit, then you may enjoy looking at the implementation in all its glory. base10 numbers, lists, associative maps and a whole lot of other madness works correctly at the type-level in ghc 6.8.2. Anyway, as the subject says, comments gratefully received. [0] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sessions-2008.2.28 [1] http://wellquite.org/non-blog/sessions-browseable/Control/Concurrent/Session/Tests.hs [2] http://wellquite.org/non-blog/sessions-browseable/doc/html/sessions/ [3] http://wellquite.org/non-blog/sessions-browseable/ Matthew -- Matthew Sackman http://www.wellquite.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Best practice for embedding files in a GHC-compiled tool?
A bit late, sorry, but you could use this: http://www.wellquite.org/hinstaller/ On Thu, Feb 7, 2008 at 5:29 AM, Dave Bayer [EMAIL PROTECTED] wrote: What is the best way to embed an arbitrary file in a Haskell program? I would like to use GHC to compile command-line tools to be used with OS X. I want the tool to be a single file, not a package or a directory, that makes no assumptions about what else is present. For example, it should be able to run as part of an OS X install disk. I want this tool to be self reproducing in the sense that one of its options causes it to output its own documentation and source code. I want this data to be stored as a compressed file within the tool binary itself. The distribution model I'm imagining here is where one writes a program anonymously, that isn't hosted anywhere but is passed from user to user because it is useful, and eventually reaches another user who wants to modify the code. Assume that intermediate users will care less about this, and will try to delete anything that they can. That rules out storing the data in a separate file. Think of the M.I.T. game Core Wars from the dawn of the computer age. I'm looking for a strategy here that will be evolutionarily successful in a fairly hostile environment. In other words, I want to be able to write in Haskell, without losing the automatic distribution of source code enjoyed by interpreted languages. No one deletes the source code for a Perl script, because by doing so they're killing the program. There must be some library I'm overlooking that would make this very easy. All I can think of is to use Template Haskell to read a compressed tar file into a Haskell variable. Is that what one does, or is there a better way? Thanks in advance, Dave ___ 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] ANNOUNCE: Sessions 2008 2 28 - RFC
On Thu, Feb 28, 2008 at 11:23 PM, Matthew Sackman [EMAIL PROTECTED] wrote: If however, you are as mad as I, and enjoy pushing the GHC type system to the limit, then you may enjoy looking at the implementation in all its glory. base10 numbers, lists, associative maps and a whole lot of other madness works correctly at the type-level in ghc 6.8.2. Only if I had known before before I recently released a library, type-level [1], which implements type-level base10 numbers and Booleans. I could have reused your implementation but didn't know about it ... The plan is to include a common type-level implementation to avoid reinventing the wheel all the time. I'm still know if people will find it useful but if they do I could include your implementation of lists and maps. What do you think? [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level-0.1 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: Hoogle 3.1
Neil, Would you consider adding auto-complete feature on Hoogle in the forth coming release? http://wiki.script.aculo.us/scriptaculous/show/Ajax.Autocompleter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: Hoogle 3.1
Hi Steve, Would you consider adding auto-complete feature on Hoogle in the forth coming release? http://wiki.script.aculo.us/scriptaculous/show/Ajax.Autocompleter I am slightly hoping that I'll be able to remove the Search button entirely, and just have results as you type. Whether that becomes feasible depends on how quickly the Hoogle search works, at the moment its way too slow, but the next version has clever data structures etc. which should make it fast enough, at least for text searches. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Wadler's blog post on the expression problem
I was reading Philip Wadler's post regarding the expression problem
and Wouter Swierstra's paper, Data Types a la Carte.
Philip asks: The instances of the injection function for subtypes are
assymmetric. Is there a symmetric solution in Haskell?
Here is a solution which works under GHC 6.8.2, heavily inspired by
the HList type computation work, available from
http://www.okmij.org/ftp/Haskell/types.html#HList
There are three keys to this trick, each of which builds on the previous.
1) TypEq: for any two types a, b, there is an instance for TypEq a b
HTrue if and only if a == b, and there is an instance for TypEq a b
HFalse otherwise.
2) This allows the definition of IsTreeMember which gives HTrue if a
type occurs somewhere within a tree and otherwise HFalse.
3) We can then use IsTreeMember as a predicate to determine whether to
use the left branch or right branch of a (:+:) constructor.
Source code follows:
{-# OPTIONS_GHC -fglasgow-exts -fallow-undecidable-instances
-fallow-overlapping-instances #-}
module Expr where
newtype Expr f = In (f (Expr f))
instance Show (f (Expr f)) = Show (Expr f) where
showsPrec _ (In x) = showParen True (showString In . showsPrec 11 x)
out :: Expr f - f (Expr f)
out (In x) = x
data (f :+: g) e = Inl (f e) | Inr (g e) deriving Show
instance (Functor f, Functor g) = Functor (f :+: g) where
fmap h (Inl f) = Inl (fmap h f)
fmap h (Inr g) = Inr (fmap h g)
class (Functor sub, Functor sup) = (::) sub sup where
inj :: sub a - sup a
instance TypTree sub sup = (::) sub sup where inj = treeInj
data Val e = Val Int deriving Show
data Add e = Add e e deriving Show
data Mul e = Mul e e deriving Show
instance Functor Val where
fmap f (Val x) = Val x
instance Functor Add where
fmap f (Add l r) = Add (f l) (f r)
instance Functor Mul where
fmap f (Mul l r) = Mul (f l) (f r)
foldExpr :: Functor f = (f a - a) - Expr f - a
foldExpr f (In t) = f (fmap (foldExpr f) t)
class Functor f = Eval f where
evalA :: f Int - Int
instance Eval Val where
evalA (Val x) = x
instance Eval Add where
evalA (Add x y) = x + y
instance Eval Mul where
evalA (Mul x y) = x * y
instance (Eval f, Eval g) = Eval (f :+: g) where
evalA (Inl f) = evalA f
evalA (Inr g) = evalA g
eval :: Eval f = Expr f - Int
eval expr = foldExpr evalA expr
val :: (Val :: e) = Int - Expr e
val x = In $ inj $ Val x
add :: (Add :: e) = Expr e - Expr e - Expr e
add x y = In $ inj $ Add x y
mul :: (Mul :: e) = Expr e - Expr e - Expr e
mul x y = In $ inj $ Mul x y
test :: Expr (Val :+: Add)
test = In (Inr (Add (val 118) (val 1219)))
test2 :: Expr (Add :+: Val)
test2 = val 1
test3 :: Expr ((Add :+: Val) :+: Mul)
test3 = add (mul (val 1) (val 2)) (val 3)
test4 :: Expr (Add :+: (Val :+: Mul))
test4 = add (mul (val 1) (val 2)) (val 3)
-- our typtree selection prefers left injection
test5 :: Expr ((Val :+: Val) :+: (Val :+: Val))
test5 = val 1
--
-- TypTree. This is basically the same as (::).
-- I kept it a separate class during development. This also allows the use of
-- additional constraints on (::) which improve the error messages
when you try,
-- for example:
-- testBroken :: Expr (Mul :+: Add)
-- testBroken = val 3
--
class (Functor sub, Functor sup) = TypTree sub sup where
treeInj :: sub a - sup a
instance Functor x = TypTree x x where
treeInj = id
--
-- The magic all happens here
-- We use IsTreeMember to determine if a type is part of a tree with leaves
-- of various types and internal nodes of type (l :+: r).
--
class IsTreeMember (sub :: * - *) (sup :: * - *) b | sub sup - b
instance TypEq x y b = IsTreeMember x y b
instance (IsTreeMember x l bl, IsTreeMember x r br, TypOr bl br b) =
IsTreeMember x (l :+: r) b
class (Functor sub, Functor l, Functor r) = TypTree' b sub l r where
treeInj' :: b - sub a - (l :+: r) a
--
-- We can then use this result to decide whether to select from the
left or the right.
--
instance (TypTree x l, Functor r) = TypTree' HTrue x l r where
treeInj' _ = Inl . treeInj
instance (TypTree x r, Functor l) = TypTree' HFalse x l r where
treeInj' _ = Inr . treeInj
--
-- Finally, this allows us to select which treeInj' to use based on the
-- type passed in.
--
instance (IsTreeMember x l b, TypTree' b x l r) = TypTree x (l :+: r) where
treeInj = treeInj' (undefined :: b)
class TypOr b1 b2 res | b1 b2 - res
instance TypOr HFalse HFalse HFalse
instance TypOr HFalse HTrue HTrue
instance TypOr HTrue HFalse HTrue
instance TypOr HTrue HTrue HTrue
-- Type equality, semi-lifted from the hlist paper; this only works in GHC.
--
-- You can avoid the reliance on GHC6.8 type equality constraints
-- by using TypeCast from the HList library instead.
--
-- see http://www.okmij.org/ftp/Haskell/types.html#HList
-- for the source of this idea.
data HFalse
data HTrue
class TypEq (x :: * - *) (y :: * - *) b | x y - b
instance TypEq x x HTrue
instance (b ~ HFalse) = TypEq x y b
___
[Haskell-cafe] Re: Wadler's blog post on the expression problem
In case you're curious, Wadler's blog post is here: http://wadler.blogspot.com/2008/02/data-types-la-carte.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error I haven't seen before
Jefferson Heard wrote:
Main: No match in record selector Protein.go_terms
data R = A { sa :: Int } | B { sb :: Int }
sa (A 0) works (as expected). sa (B 0) gives
*** Exception: No match in record selector Main.sa
I think that explains your problem.
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Re: [Haskell-cafe] Re: ANN: Hoogle 3.1
You can try aggressive caching and indexing (which google uses often) based on 20-80 rule. http://en.wikipedia.org/wiki/Pareto_principle On Thu, Feb 28, 2008 at 7:49 PM, Neil Mitchell [EMAIL PROTECTED] wrote: Hi Steve, Would you consider adding auto-complete feature on Hoogle in the forth coming release? http://wiki.script.aculo.us/scriptaculous/show/Ajax.Autocompleter I am slightly hoping that I'll be able to remove the Search button entirely, and just have results as you type. Whether that becomes feasible depends on how quickly the Hoogle search works, at the moment its way too slow, but the next version has clever data structures etc. which should make it fast enough, at least for text searches. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANN: Hoogle 3.1
Hi You can try aggressive caching and indexing (which google uses often) based on 20-80 rule. The Hoogle logs suggest this wouldn't be that useful. The most commonly invoked searches are the three listed on the front page. After that, the most common search is actually for where, at under 1%. However, there are other ways I think I can get the necessary speed, and autocomplete would be very useful. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Error I haven't seen before
It does. Thank you...
On Thu, Feb 28, 2008 at 5:00 PM, Albert Y. C. Lai [EMAIL PROTECTED] wrote:
Jefferson Heard wrote:
Main: No match in record selector Protein.go_terms
data R = A { sa :: Int } | B { sb :: Int }
sa (A 0) works (as expected). sa (B 0) gives
*** Exception: No match in record selector Main.sa
I think that explains your problem.
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--
I try to take things like a crow; war and chaos don't always ruin a picnic,
they just mean you have to be careful what you swallow.
-- Jessica Edwards
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Re: [Haskell-cafe] to stimulate discussion concerning where Haskell is going .. ...
--- Galchin Vasili [EMAIL PROTECTED] wrote: [snip] I have fished around and collected some Sun papers and slides. If any anybody wants I can post the URLs or send to the interested Yes, I am interested. Please post the URLs, and I will flag the message and refer to the associated pages as soon as I have time. Benjamin L. Russell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
