Re: [Haskell-cafe] More documentation: how to create a Haskell project
[EMAIL PROTECTED] (Donald Bruce Stewart) writes: But we could do with more information on: [...] How to make cabal projects into distribution-specific (.deb, .rpm, and so on) packages? -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mapAccumL - find max in-sequence subsequence
It's a pity that groupBy isn't defined a little differently: -- @'groupBy' rel xs@ returns the shortest list of lists such that -- -- * the concatenation of the lists is @xs@, and -- -- * @rel@ is 'True' for each consecutive pair of elements in a sublist. -- groupBy :: (a - a - Bool) - [a] - [[a]] groupBy rel [] = [] groupBy rel (x:xs) = (x:ys) : groupBy rel zs where (ys,zs) = groupByAux x xs groupByAux x0 (x:xs) | rel x0 x = (x:ys, zs) where (ys,zs) = groupByAux x xs groupByAux y xs = ([], xs) That's equivalent to the existing definition if rel is symmetric and transitive, but also useful in other cases, e.g. groupBy (=) would generate a list of runs, and the solution to the problem here would be longestInSequence :: (Enum a, Eq a) = [a] - Int longestInSequence = maximum . map length . groupBy adjacent where adjacent x y = succ x == y ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Deriving class instances using DrIFT
On 29.10 19:56, John Meacham wrote: Since DrIFT can only understand haskell source code, it can't derive instances for anything you don't have the original source to. such as things in the pre-compiled libraries that come with ghc. you will likely have to write out those instances by hand. Another possibility is that you could replicate just the data declarations by hand, and use DrIFT -r to just spit out the derivations and put those in a file on their own. How about using Template Haskell for getting the definition and then giving that to DrIFT? - Einar Karttunen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More documentation: how to create a Haskell project
Ketil Malde wrote: How to make cabal projects into distribution-specific (.deb, .rpm, and so on) packages? The answer for .debs is: ask a Debian developer (or a prospective developer) to package it for you. The reason is that to make a good .deb, one needs to be familiar with a lot of Debian-specific policies and technologies. If one is willing to invest the time and effort to learn this, then it makes sense for one to apply to become a Debian developer. If not, then packaging is best left for someone else. -- Antti-Juhani Kaijanaho, Debian developer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More documentation: how to create a Haskell project
On Mon, Oct 30, 2006 at 09:54:08AM +0100, Ketil Malde wrote: How to make cabal projects into distribution-specific (.deb, .rpm, and so on) packages? for slackware you can have a look to this slackBuild script: http://gorgias.mine.nu/repos/slackBuild/hxt/hxt/hxt.SlackBuild regards, andrea ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] More documentation: how to create a Haskell project
On 30/10/06, Tony Morris [EMAIL PROTECTED] wrote: 4) If you want links to base libraries in your haddock output, do such and such (how do you do that anyway?) I believe you need a local copy of the library sources, whose path you give to haddock with some flag. -- -David House, [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] More documentation: how to create a Haskell project
Hello Tony, Monday, October 30, 2006, 6:22:31 AM, you wrote: My suggestion: The steps of reasoning as you start with a blank directory. For example: great idea! i'm sure that such sort of manual will be very helpful for anyone starting his first haskell project -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Simple GADT parser for the eval example
I'm trying to create a simple parser for the GADT evaluator from the wobbly types paper, and I need a little help. Here's the GADT and the evaluator... data Term a where Lit :: Int - Term Int Inc :: Term Int - Term Int IsZ :: Term Int - Term Bool If :: Term Bool - Term a - Term a - Term a Pair :: Term a - Term b - Term (a,b) Fst :: Term (a,b) - Term a Snd :: Term (a,b) - Term b eval :: Term a - a eval (Lit i)= i eval (Inc t)= eval t + 1 eval (IsZ t)= eval t == 0 eval (If b t e) = if eval b then eval t else eval e eval (Pair a b) = (eval a, eval b) eval (Fst t)= fst (eval t) eval (Snd t)= snd (eval t) ...and instead of writing my own read instance, I thought I'd take a shortcut and just try converting a regular data type to our generalized one... data Expr = ELit Int | EInc Expr | EIsZ Expr | EPair Expr Expr | EIf Expr Expr Expr | EFst Expr | ESnd Expr deriving (Read,Show) my_read' :: Expr - Term a my_read' (ELit a) = Lit a my_read' (EInc a) = Inc (my_read' a) my_read' (EIsZ a) = IsZ (my_read' a) my_read' (EPair a b) = Pair (my_read' a) (my_read' b) my_read' (EIf p t e) = If (my_read' p) (my_read' t) (my_read' e) my_read' (EFst a) = Fst (my_read' a) my_read' (ESnd a) = Snd (my_read' a) ...That looks nice and simple, but it doesn't type check. GHCi-6.6 complains... Couldn't match expected type `a' (a rigid variable) against inferred type `Int' `a' is bound by the type signature for `my_read' at eval_gadt_wobbly.hs:45:24 Expected type: Term a Inferred type: Term Int In the expression: Lit a In the definition of `my_read': my_read (ELit a) = Lit a ...No surprise there, since there is no way to fail in the event of a maltyped Expr. The next thing to try is a type class solution... class MyRead a where my_read :: Expr - Term a instance MyRead Int where my_read (ELit a) = Lit a my_read (EInc a) = Inc (my_read a) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) my_read (EFst a) = Fst (my_read a :: MyRead b = Term (Int,b)) --my_read (ESnd a) = Snd (my_read a) instance MyRead Bool where my_read (EIsZ a) = IsZ (my_read a) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) --my_read (EFst a) = Fst (my_read a) --my_read (ESnd a) = Snd (my_read a) instance (MyRead a, MyRead b) = MyRead (a,b) where my_read (EPair a b) = Pair (my_read a) (my_read b) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) --my_read (EFst a) = Fst (my_read a) --my_read (ESnd a) = Snd (my_read a) This just about works, except for the definitions for the Fst and Snd constructors. The compiler complains... Ambiguous type variable `b' in the constraint: `MyRead b' arising from use of `my_read' at eval_gadt_wobbly.hs:65:28-36 Probable fix: add a type signature that fixes these type variable(s) ...Of course, that makes perfect sense, since, if we're applying Fst to a term, then we don't care about the other branch of the Pair. You can get it accepted by the type checker by making the types more concrete... my_read (EFst a) = Fst (my_read a :: Term (Int,Int)) ...or... my_read (EFst a) = Fst (my_read a :: Term (Int,Bool)) ...but how does a person fix this to work in the more general case? Or is this even the right way to build a parser for the GADT evaluator example? Notice the repetition needed: the If, Fst, and Snd defintions have to be copied to all three instances. Also, feel free to comment on this example, and the fact that it will evaluate with no problems. static_vs_laziness = eval (my_read (EIf (EIsZ (ELit 0)) (ELit 9) (EIsZ (ELit 42)))::Term Int) Thanks, Greg Buchholz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] monadic performance
On 10/28/06, Tomasz Zielonka [EMAIL PROTECTED] wrote: On Fri, Oct 27, 2006 at 06:28:58AM -0700, Chad Scherrer wrote: Should I expect a monadic version to take a performance hit? What if I use some SPECIALIZE pragmas or somesuch? Is it more efficient to write one from scratch, or do specific type annotations give me the same thing anyway? That's good to hear, thanks! At this point my biggest concern is whether the strict parts and lazy parts will play nice. Everything about my data structure is strict, and thinking about how a Writer monad would interact with that just makes me confused, so far. -Chad ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Deriving class instances using DrIFT
On Monday 30 October 2006 22:18, Einar Karttunen wrote: On 29.10 19:56, John Meacham wrote: Since DrIFT can only understand haskell source code, it can't derive instances for anything you don't have the original source to. Ahhh, ok. such as things in the pre-compiled libraries that come with ghc. you will likely have to write out those instances by hand. Hmmm, seems strange that it can successfully derive for the Data.Maybe type but not the Data.Word32 type. I didn't think it would have access to any original source from my ghc install, there only seems to be hi files. Another possibility is that you could replicate just the data declarations by hand, and use DrIFT -r to just spit out the derivations and put those in a file on their own. How about using Template Haskell for getting the definition and then giving that to DrIFT? Thanks for the suggestions. Daniel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Accumulating related XML nodes using HXT
Hello. I have some html from which I want to extract records. Each record is represented within a number of tr nodes, and all records tr nodes are contained by the same parent node. The things I've tried so far end up giving me the cartesian product of record fields, so for the html fragment included below I'd end up with: [ Prod Television 17 /prod17 A very nice telly. , Prod Television 17 /prod17 Mind your fillings. , Prod Cyclotron 24 /prod24 A very nice telly. , Prod Cyclotron 24 /prod24 Mind your fillings. ] instead of: [ Prod Television 17 /prod17 A very nice telly. , Prod Cyclotron 24 /prod24 Mind your fillings. ] How should I go about accumulating related tr nodes into individual records? Thanks Daniel HTML fragment follows: ... tr tr tdstrongProduct:/strong/td tdstronga href=/prod17Television/a/strong (code: 17)/td /tr tr tdstrongDescription:/strong/td tdA very nice telly./td /tr tr tdhr color=#0/td /tr tr tdstrongProduct:/strong/td tdstronga href=/prod24Cyclotron/a/strong (code: 24)/td /tr tr tdstrongDescription:/strong/td tdMind your fillings./td /tr tr tdhr color=#0/td /tr /tr ... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Deriving class instances using DrIFT
On Tue, Oct 31, 2006 at 07:46:05AM +1300, Daniel McAllansmith wrote: Hmmm, seems strange that it can successfully derive for the Data.Maybe type but not the Data.Word32 type. I didn't think it would have access to any original source from my ghc install, there only seems to be hi files. It has a few data definitions built into it. Bool,Maybe,Either, and Ordering. see src/PreludData.hs for how that is done. John -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple GADT parser for the eval example
I don't have an answer, but would be extremely interested in knowing one! one of my first attempts to use GADTs was to do something similar, implemening the simple polymorphic lambda calculus in a way that transformations could be guarenteed typesafe statically, but then when I went and tried to write an interpreter, I couldn't figure out how to read in programs to interpret. it seems you would want something like first class existentials 'Exp (exists a . a)' or something like that. John -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple GADT parser for the eval example
Hi Greg, We've built some GADT parsers recently to fit our two-level transformation library with front-ends for for XML Schema and SQL. See Coupled Schema Transformation and Data Conversion For XML and SQL (PADL 2007) if you're interested. The trick is to use a constructor in which the a variable of Term a is existentially quantified. For example: data DynTerm where DynTerm :: Type a - Term a - DynTerm (I'm using GADT notation here, but normal ADT syntax would do just fine as well.) The first argument is the folklore GADT for representing types: data Type a where Int :: Type Int Bool :: Type Bool Prod :: Type a - Type b - Type (a,b) Then you can write your parser function with the following type: my_read' :: Expr - DynTerm Or, more likely: my_read' :: Expr - Maybe DynTerm with: my_read' (ELit a)= return $ DynTerm Int (Lit a) my_read' (EInc a)= do DynTerm Int a' - my_read' a return (DynTerm Int (Inc a')) Then you call eval something like: test :: Expr - Maybe Dynamic test expr = do DynTerm t a - my_read' expr return (Dyn t (eval a)) The Dynamic is defined as: data Dynamic where Dyn :: Type a - a - Dynamic The dynamic typing trick here is due to Swierstra and Baars. For further processing of the Dynamic result, you'll need to write functions with a type like: f :: Type a - a - X A typical example: gshow :: Type a - a - String gshow Int i = show i gshow Bool b = show b gshow (Prod a b) (x,y) = (++gshow a x++,++gshow b y++) Hope this helps. Source code is attached. Best, Joost On Oct 30, 2006, at 5:00 PM, Greg Buchholz wrote: I'm trying to create a simple parser for the GADT evaluator from the wobbly types paper, and I need a little help. Here's the GADT and the evaluator... data Term a where Lit :: Int - Term Int Inc :: Term Int - Term Int IsZ :: Term Int - Term Bool If :: Term Bool - Term a - Term a - Term a Pair :: Term a - Term b - Term (a,b) Fst :: Term (a,b) - Term a Snd :: Term (a,b) - Term b eval :: Term a - a eval (Lit i)= i eval (Inc t)= eval t + 1 eval (IsZ t)= eval t == 0 eval (If b t e) = if eval b then eval t else eval e eval (Pair a b) = (eval a, eval b) eval (Fst t)= fst (eval t) eval (Snd t)= snd (eval t) ...and instead of writing my own read instance, I thought I'd take a shortcut and just try converting a regular data type to our generalized one... data Expr = ELit Int | EInc Expr | EIsZ Expr | EPair Expr Expr | EIf Expr Expr Expr | EFst Expr | ESnd Expr deriving (Read,Show) my_read' :: Expr - Term a my_read' (ELit a) = Lit a my_read' (EInc a) = Inc (my_read' a) my_read' (EIsZ a) = IsZ (my_read' a) my_read' (EPair a b) = Pair (my_read' a) (my_read' b) my_read' (EIf p t e) = If (my_read' p) (my_read' t) (my_read' e) my_read' (EFst a) = Fst (my_read' a) my_read' (ESnd a) = Snd (my_read' a) ...That looks nice and simple, but it doesn't type check. GHCi-6.6 complains... Couldn't match expected type `a' (a rigid variable) against inferred type `Int' `a' is bound by the type signature for `my_read' at eval_gadt_wobbly.hs:45:24 Expected type: Term a Inferred type: Term Int In the expression: Lit a In the definition of `my_read': my_read (ELit a) = Lit a ...No surprise there, since there is no way to fail in the event of a maltyped Expr. The next thing to try is a type class solution... class MyRead a where my_read :: Expr - Term a instance MyRead Int where my_read (ELit a) = Lit a my_read (EInc a) = Inc (my_read a) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) my_read (EFst a) = Fst (my_read a :: MyRead b = Term (Int,b)) --my_read (ESnd a) = Snd (my_read a)instance MyRead Bool where my_read (EIsZ a) = IsZ (my_read a) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) --my_read (EFst a) = Fst (my_read a) --my_read (ESnd a) = Snd (my_read a) instance (MyRead a, MyRead b) = MyRead (a,b) where my_read (EPair a b) = Pair (my_read a) (my_read b) my_read (EIf p t e) = If (my_read p) (my_read t) (my_read e) --my_read (EFst a) = Fst (my_read a) --my_read (ESnd a) = Snd (my_read a) This just about works, except for the definitions for the Fst and Snd constructors. The compiler complains... Ambiguous type variable `b' in the constraint: `MyRead b' arising from use of `my_read' at eval_gadt_wobbly.hs:65:28-36 Probable fix: add a type signature that fixes these type variable(s) ...Of course, that makes perfect sense, since, if we're applying Fst to a term, then we don't care about the other branch of the Pair. You can get it accepted by the type checker by making the types more concrete... my_read (EFst a) = Fst (my_read a :: Term (Int,Int)) ...or... my_read (EFst a) = Fst (my_read a ::
Re: [Haskell-cafe] Simple GADT parser for the eval example
Just noticed Joost Visser's message but since I
had (essentially a very similar) response I thought I might
send it off as well ... It includes the conditional cases.
Regards,
-d
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main where
data Term a where
Lit :: Int - Term Int
Inc :: Term Int - Term Int
IsZ :: Term Int - Term Bool
If :: Term Bool - Term a - Term a - Term a
Pair :: Term a - Term b - Term (a,b)
Fst :: Term (a,b) - Term a
Snd :: Term (a,b) - Term b
data Expr = ELit Int
| EInc Expr
| EIsZ Expr
| EPair Expr Expr
| EIf Expr Expr Expr
| EFst Expr
| ESnd Expr
deriving (Read,Show)
-- Give a GADT for representation types
data R a where
Rint :: R Int
Rbool :: R Bool
Rpair :: R a - R b - R (a,b)
-- Give an existential type with a type representation
data TermEx where
MkTerm :: R a - Term a - TermEx
-- we use Weirich's higher-order type-safe cast to avoid deep traversals
-- one can replace the type_cast with a more simple traversal-based
-- version.
data CL c a d = CL (c (d,a))
data CR c a d = CR (c (a,d))
type_cast :: forall a b c. R a - R b - c a - c b
type_cast Rint Rint x = x
type_cast Rbool Rbool x = x
type_cast (Rpair (ra::(R a0)) (rb::(R b0)))
(Rpair (ra'::(R a0')) (rb'::(R b0'))) x =
let g = (type_cast ra ra' :: ( (CL c b0) a0 - (CL c b0) a0' ))
h = (type_cast rb rb' :: ( (CR c a0') b0 - (CR c a0') b0'))
in case (g (CL x)) of
CL x' - case (h (CR x')) of
CR y' - y'
type_cast _ _ _ = error cannot cast!
-- give only the cases for Eif and Elit, the others are similar
my_read :: Expr - TermEx
my_read (ELit i) = MkTerm Rint (Lit i);
my_read (EIf p t e) =
case (my_read p) of
MkTerm rb b -
case rb of
Rbool -
case (my_read t) of
MkTerm r1 t1 -
case (my_read e) of
MkTerm r2 t2 -
MkTerm r2 (If b (type_cast r1 r2 t1) t2)
_ - error conditional not boolean!
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[Haskell-cafe] YAHT: searchAll5
I can't get searchAll5[1] in Yet Another Haskell Tutorial to run. Ghci complains that it can't find a MonadPlus that satisfies the required type; it needs a MonadPlus. I suspect this is due to the use of 'mzero' and 'mplus', without making StateT a MonadPlus. My thought for this was to push mzero into the inner monad and have 'mplus' pass on to the inner monad: instance Monad m = MonadPlus (StateT state m) where mzero = StateT (\s - return (s, mzero)) (StateT m1) `mplus` (StateT m2) = StateT (\s - do (s1, a) - m1 s (s2, b) - m2 s1 return (s2, a `mplus` b)) What's above isn't accepted by ghci, and I don't even know for sure that my thought makes sense. /M [1]: http://en.wikibooks.org/wiki/Haskell/YAHT/Monads#Monad_Transformers -- Magnus Therning (OpenPGP: 0xAB4DFBA4) [EMAIL PROTECTED] Jabber: [EMAIL PROTECTED] http://therning.org/magnus Software is not manufactured, it is something you write and publish. Keep Europe free from software patents, we do not want censorship by patent law on written works. Finagle's Fifth Law: Always draw your curves, then plot your readings. pgpCi3BAvGSwu.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] YAHT: searchAll5
Disclaimer: I've never read through YAHT, so I don't know if I'm missing any context... Your intuition was correct: you do want to lift the MonadPlus property through the StateT transformer. This is the key to the transformer libraries, each transformer both contributes a computational feature (MonadState, MonadReader, MonadPlus, MonadError, ...) as well as maintains all features of the monad it's transforming. You've noticed that we need an instance in order to have the StateT monad transformer maintain the MonadPlus property of its inner monad. Beyond the encouragement that your intuition was dead on, I would suggest tryng to use mzero and mplus sooner than you are doing so. In other words, your method defintions should be simpler. Good luck! Nick On 10/30/06, Magnus Therning [EMAIL PROTECTED] wrote: I can't get searchAll5[1] in Yet Another Haskell Tutorial to run. Ghci complains that it can't find a MonadPlus that satisfies the required type; it needs a MonadPlus. I suspect this is due to the use of 'mzero' and 'mplus', without making StateT a MonadPlus. My thought for this was to push mzero into the inner monad and have 'mplus' pass on to the inner monad: instance Monad m = MonadPlus (StateT state m) where mzero = StateT (\s - return (s, mzero)) (StateT m1) `mplus` (StateT m2) = StateT (\s - do (s1, a) - m1 s (s2, b) - m2 s1 return (s2, a `mplus` b)) What's above isn't accepted by ghci, and I don't even know for sure that my thought makes sense. /M [1]: http://en.wikibooks.org/wiki/Haskell/YAHT/Monads#Monad_Transformers -- Magnus Therning (OpenPGP: 0xAB4DFBA4) [EMAIL PROTECTED] Jabber: [EMAIL PROTECTED] http://therning.org/magnus Software is not manufactured, it is something you write and publish. Keep Europe free from software patents, we do not want censorship by patent law on written works. Finagle's Fifth Law: Always draw your curves, then plot your readings. ___ 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
