Re: [Haskell-cafe] Using a monad to decompose a function into functions
2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: On Thursday 12 March 2009, you wrote: 2009/3/12 Marcin Kosiba marcin.kos...@gmail.com: Hi, I'm doing a bit of research into mobility models and I'm currently exploring implementation language choices for the simulator (*snip*) The simulation algorithm requires expressing the node's mobility so that it is stateless. The mobility model algorithm's type should be something like: mobility_model :: WorldState - NodeState - OtherInput - (Action, NodeState) where Action can alter WorldState and the second NodeState is an altered input NodeState. I perform a form of speculative execution on mobility_model so sometimes I need to backtrack to a previous world and node state. This is all fairly simple stuff, and was just an introduction. What I do now is store an enum in NodeState and implement mobility_model as one big case statement. Yes, this is very imperative of me, I know. What I'd like to do is to express mobility_model, so that the code would look like: mobility_model world node input = do do_calculus emit_action if something then emit_action else emit_action do_calculus emit_action mobility_model world node input Hi, It seems you can use http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Mon ad-State-Lazy.html Just have a look at the exemple : tick :: State Int Int tick = do n - get put (n+1) return n your code would become something like mobility_model :: OtherInput - State (WorldState,NodeState) () mobility_model input = do world - gets fst node - gets snd let (world',node') = ... put (world',node') ok, that solves part of the problem. what this doesn't solve is that somewhere between these lines (which corespond to emit_action in my example) let (world',node') = ... put (world',node') I need to return a value and an Action and NodeState to the simulation algorithm. and then, after the simulation algorithm calculates a new WorldState it will want the mobility_model to where it left off, but with a new WorldState. I hope I'm clear about what I wish to achieve: each emit_action should return a value (Action, NodeState) and maybe a function mobility_model_cont which I then could call with the new WorldState to continue from where emit_action returned. I'm not entirely sure ... but I think it doesn't matter that much :) Here is why. This was just an exemple : mobility_model :: OtherInput - State (WorldState,NodeState) () You could also have mobility_model :: OtherInput - NodeState - State WorldState (NodeState,Action) or whatever. In fact, the State monad makes it easy to thread (in this context, it means 'pass around') an argument to many functions, providing a nice syntax reminiscent of imperative language. But it lets you completely free of what is passed around. It depends on what you want to be explicitely passed by argument, and what you want to pass in the state of the monad (that is, what you want to appear, inside the monad only, as some global variable). So in your code, if you often need to pass a WorldState to a function which should return a modified WorldState, it makes sense to put WorldState inside the state monad. But, maybe, if there is just a few functions which act on NodeState, it has not to be part of the state carried by the state monad. I'm not entirely sure of what is a problem to you : is it the use of the State monad, or something else ? If it can help you to formulate your question you can post some code (or past it to http://hpaste.org/)... Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to compare PortNumbers or Bug in Network.Socket?
On Thu, Mar 12, 2009 at 8:45 PM, Antoine Latter aslat...@gmail.com wrote: So the Ord instance is wrong for the PortNumber type? Well, maybe not wrong. It's out and out wrong. You get different results on machines of different endianness. Now, this begs the question of why not just simply use an unwrapped Word16 instead :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Dynamically typing TH.Exp at runtime
Sorry, maybe it I didn't made it clear enough. Perhaps I'm misunderstanding something, but since one can infer types in GHCI, that implies one can infer types in the GHC API; since Hint wraps the GHC API, that implies one can infer types in Hint, doesn't it? And indeed, there are functions to infer the type of a String; iirc I've even used them myself in mueval. That's true, inferring the type of a string is not the problem. However, I am not only interested in the top-level type, but also in the type of any arbitrary subexpression. Consider for example following recursive definition: foo [] = [] foo (x:xs) = (:)(x+1)(foo xs) Typing only the first rule one would says its type is '[a] - [a]'. However, the second rule specialises the type to 'Num a = [a] - [a]'. So, if I am interested in the type of the 'x' in the pattern of the second rule, I need to be aware of its binding on the right-hand side. Consequently the type of 'x' is 'Num a'. AFAIK, I need Hendley-Milner type inference for that (please correct me if I am wrong) and I was wondering if I really need to implement it by myself, when it is already somewhere inside GHC. Thanks, Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Sugestion for a Haskell mascot
Am Donnerstag, 12. März 2009 22:00 schrieb Martijn van Steenbergen: Deniz Dogan wrote: Then of course, there's the downside that there's no connection to the language itself in any way. I usually go for names that don't have to do anything with the application itself: GroteTrap (translates to GreatBustard), Yogurt, Custard... saves me from having to think of appropriate names. :-P This is basically how I chose the name “Grapefruit” for “my” FRP library. Okay, it refers to Fruit (a FRP GUI library) but the only further meaning of “Grapefruit” is that I find Grapefruits to be tasty. :-) Often people choose meaningful names and convert them to acronyms, noone can pronounce. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Combining haddock documentation from multiple packages
Hi Heikki, Heikki Aitakangas wrote: Is it possible to generate a unified documentation tree similar to http://www.haskell.org/ghc/docs/latest/html/libraries/index.html from packages installed via cabal from hackage? And if so, how does one go about doing it? This question was asked recently. See: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/53531 Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
Hi Mark, On Mar 13, 2009, at 3:54 AM, Mark Spezzano wrote: I was wondering what the best way to implement Natural number would be. Is there a package which already does this? there are two packages on Hackage that implement natural numbers using algebraic datatypes: 'numbers' has a module Data.Number.Natural that implements them in unary notation (zero and successor), 'nat' has Data.Number.Nat that uses a binary encoding. Cheers, Sebastian___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Against cuteness
Am Freitag, 13. März 2009 04:29 schrieb Benjamin L.Russell: Consider the following logo: Silver red monad.png http://commons.wikimedia.org/wiki/File:Silver_red_monad.png Can’t we choose something which is not connected to certain worldviews? Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] State monad is missing Applicative instance
Am Freitag, 13. März 2009 05:09 schrieb Denis Bueno: This works because every monad induces an Applicative instance in a way I've ingested just enough wine to forget. =] pure = return (*) = ap Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
* Alexander Dunlap alexander.dun...@gmail.com [2009-03-12 20:01:57-0700] Also, a lot of functions just take Integers so it would be more of a pain to use. AFAIK there are very few fuctions that take Integers. Many functions take instances of Integral, but it's not a problem to make your own type such an instance. -- Roman I. Cheplyaka :: http://ro-che.info/ Don't let school get in the way of your education. - Mark Twain ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
Am Freitag, 13. März 2009 04:01 schrieb Alexander Dunlap: 2. Use the type data Natural = Zero | Succ !Natural […] In terms of speed, I think that [3] would be reasonably fast (unless you do a ton of subtraction with bounds-checking) and [2] would probably be quite slow, because you don't get the speed-boost from doing computations right on the processor. Not only that but also because operations like addition now take at least linear time. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
Am Freitag, 13. März 2009 04:53 schrieb Brandon S. Allbery KF8NH: On 2009 Mar 12, at 22:54, Mark Spezzano wrote: I was wondering what the best way to implement Natural number would be. Is there a package which already does this? type-level on Hackage. I think, the original poster wanted value-level naturals, not type-level naturals. 2. Use the type data Natural = Zero | Succ !Natural One of the reasons people use type-level naturals is to get laziness; you've made this strict. Is there a reason? Do you really mean type-level naturals? The following is a definition of value-level naturals: data Natural = Zero | Succ Natural Type-level naturals would be defined like this: data Zero data Succ nat Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using a monad to decompose a function into functions
On Friday 13 March 2009, you wrote: 2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: On Thursday 12 March 2009, you wrote: 2009/3/12 Marcin Kosiba marcin.kos...@gmail.com: Hi, I'm doing a bit of research into mobility models and I'm currently exploring implementation language choices for the simulator (*snip*) The simulation algorithm requires expressing the node's mobility so that it is stateless. The mobility model algorithm's type should be something like: mobility_model :: WorldState - NodeState - OtherInput - (Action, NodeState) where Action can alter WorldState and the second NodeState is an altered input NodeState. I perform a form of speculative execution on mobility_model so sometimes I need to backtrack to a previous world and node state. This is all fairly simple stuff, and was just an introduction. What I do now is store an enum in NodeState and implement mobility_model as one big case statement. Yes, this is very imperative of me, I know. What I'd like to do is to express mobility_model, so that the code would look like: mobility_model world node input = do do_calculus emit_action if something then emit_action else emit_action do_calculus emit_action mobility_model world node input Hi, It seems you can use http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control- Mon ad-State-Lazy.html Just have a look at the exemple : tick :: State Int Int tick = do n - get put (n+1) return n your code would become something like mobility_model :: OtherInput - State (WorldState,NodeState) () mobility_model input = do world - gets fst node - gets snd let (world',node') = ... put (world',node') ok, that solves part of the problem. what this doesn't solve is that somewhere between these lines (which corespond to emit_action in my example) let (world',node') = ... put (world',node') I need to return a value and an Action and NodeState to the simulation algorithm. and then, after the simulation algorithm calculates a new WorldState it will want the mobility_model to where it left off, but with a new WorldState. I hope I'm clear about what I wish to achieve: each emit_action should return a value (Action, NodeState) and maybe a function mobility_model_cont which I then could call with the new WorldState to continue from where emit_action returned. I'm not entirely sure ... but I think it doesn't matter that much :) Here is why. This was just an exemple : mobility_model :: OtherInput - State (WorldState,NodeState) () You could also have mobility_model :: OtherInput - NodeState - State WorldState (NodeState,Action) or whatever. In fact, the State monad makes it easy to thread (in this context, it means 'pass around') an argument to many functions, providing a nice syntax reminiscent of imperative language. But it lets you completely free of what is passed around. It depends on what you want to be explicitely passed by argument, and what you want to pass in the state of the monad (that is, what you want to appear, inside the monad only, as some global variable). So in your code, if you often need to pass a WorldState to a function which should return a modified WorldState, it makes sense to put WorldState inside the state monad. But, maybe, if there is just a few functions which act on NodeState, it has not to be part of the state carried by the state monad. I'm not entirely sure of what is a problem to you : is it the use of the State monad, or something else ? If it can help you to formulate your question you can post some code (or past it to http://hpaste.org/)... Threading the state is not the problem. Maybe this will help: what I have now: fsm world state = case state of first - do_stuff_one (move_up, succ state) second - do_stuff_two (move_left, succ state) third - do_stuff_three (move_right, first) what I'd want to have is to say: fsm world state = do do_stuff_one yield move_up do_stuff_two yield move_left do_stuff_three yield move_right fsm world state and have it translated to: fsm world state = do_stuff_one (move_up, \world' state' - do_stuff_two (move_left, \world'' state'' - do_stuff_three (move_right, fsm world'' state'') Thanks! Marcin Kosiba signature.asc Description: This is a digitally signed message part. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
Am Freitag, 13. März 2009 09:21 schrieb Roman Cheplyaka: * Alexander Dunlap alexander.dun...@gmail.com [2009-03-12 20:01:57-0700] Also, a lot of functions just take Integers so it would be more of a pain to use. AFAIK there are very few fuctions that take Integers. Many functions take instances of Integral, but it's not a problem to make your own type such an instance. I’d say that it is a problem. Class instances should satisfy certain laws. (Although these laws are often not stated explicitely, they are assumed to hold by users of the class and they should hold to make the instance sensible.) In the case of Num, I would expect num + negate num to equal num. This wouldn’t hold for a Natural instance of Num. Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using a monad to decompose a function into functions
2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: On Friday 13 March 2009, you wrote: 2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: On Thursday 12 March 2009, you wrote: 2009/3/12 Marcin Kosiba marcin.kos...@gmail.com: Hi, I'm doing a bit of research into mobility models and I'm currently exploring implementation language choices for the simulator (*snip*) The simulation algorithm requires expressing the node's mobility so that it is stateless. The mobility model algorithm's type should be something like: mobility_model :: WorldState - NodeState - OtherInput - (Action, NodeState) where Action can alter WorldState and the second NodeState is an altered input NodeState. I perform a form of speculative execution on mobility_model so sometimes I need to backtrack to a previous world and node state. This is all fairly simple stuff, and was just an introduction. What I do now is store an enum in NodeState and implement mobility_model as one big case statement. Yes, this is very imperative of me, I know. What I'd like to do is to express mobility_model, so that the code would look like: mobility_model world node input = do do_calculus emit_action if something then emit_action else emit_action do_calculus emit_action mobility_model world node input Hi, It seems you can use http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control- Mon ad-State-Lazy.html Just have a look at the exemple : tick :: State Int Int tick = do n - get put (n+1) return n your code would become something like mobility_model :: OtherInput - State (WorldState,NodeState) () mobility_model input = do world - gets fst node - gets snd let (world',node') = ... put (world',node') ok, that solves part of the problem. what this doesn't solve is that somewhere between these lines (which corespond to emit_action in my example) let (world',node') = ... put (world',node') I need to return a value and an Action and NodeState to the simulation algorithm. and then, after the simulation algorithm calculates a new WorldState it will want the mobility_model to where it left off, but with a new WorldState. I hope I'm clear about what I wish to achieve: each emit_action should return a value (Action, NodeState) and maybe a function mobility_model_cont which I then could call with the new WorldState to continue from where emit_action returned. I'm not entirely sure ... but I think it doesn't matter that much :) Here is why. This was just an exemple : mobility_model :: OtherInput - State (WorldState,NodeState) () You could also have mobility_model :: OtherInput - NodeState - State WorldState (NodeState,Action) or whatever. In fact, the State monad makes it easy to thread (in this context, it means 'pass around') an argument to many functions, providing a nice syntax reminiscent of imperative language. But it lets you completely free of what is passed around. It depends on what you want to be explicitely passed by argument, and what you want to pass in the state of the monad (that is, what you want to appear, inside the monad only, as some global variable). So in your code, if you often need to pass a WorldState to a function which should return a modified WorldState, it makes sense to put WorldState inside the state monad. But, maybe, if there is just a few functions which act on NodeState, it has not to be part of the state carried by the state monad. I'm not entirely sure of what is a problem to you : is it the use of the State monad, or something else ? If it can help you to formulate your question you can post some code (or past it to http://hpaste.org/)... Threading the state is not the problem. Maybe this will help: what I have now: fsm world state = case state of first - do_stuff_one (move_up, succ state) second - do_stuff_two (move_left, succ state) third - do_stuff_three (move_right, first) what I'd want to have is to say: fsm world state = do do_stuff_one yield move_up do_stuff_two yield move_left do_stuff_three yield move_right fsm world state and have it translated to: fsm world state = do_stuff_one (move_up, \world' state' - do_stuff_two (move_left, \world'' state'' - do_stuff_three (move_right, fsm world'' state'') Sorry, I never used continuations or coroutines in Haskell. But, if your goal is to be less imperative, I'm not sure using 'yield' is what you want. If what you do is well expressed by a fsm, maybe you should stick to it. Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Does anybody dislike implicit params as much as I do?
Thomas Hartman wrote: http://blog.patch-tag.com/2009/03/09/implicitparams-are-evil-thoughts-on-adapting-gitit/ I understand there are arguments for using IPs, but after this experience, the ImplicitParams extension is a code smell for me. It's not just you. Implicit parameters are a scourge on the language. I think there are also some subtle annoyances with how they make apparently 'safe' program rearrangements unsafe, by pushing around let ?foo = bar in ... bindings. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Typing Dynamic Typing [Was: Dynamically typing TH.Exp at runtime]
Thanks a lot for the detailed answer. I must admit, I haven't understood it completely yet, so please excuse for probably naive questions. As far as I see from the language defined in Incope.hs, there is only support for the defined primitive functions (add, mult, if_, etc.). Using additional functions, I would need to extend it, right? Also considering Haskell as underlying language using TH as AST is not possible, because it is polymorphic? Thanks, Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Fwd: [Haskell-cafe] DSLs with {in,}equalities
-- Forwarded message --
From: Alberto G. Corona agocor...@gmail.com
Date: 2009/3/13
Subject: Re: [Haskell-cafe] DSLs with {in,}equalities
To: Adam Vogt vogt.a...@gmail.com
You need an expression evaluator:
with
(+) (Const a) (Const b)= Const (a+b)
(*) (Const a) (Const b)= Const (a*b)
eval :: Exp - Integer
eval (Const i)= i
eval ( Plus e1 e2)= eval e1 + eval e2 ..
eval( Mul
and
instance Ord Expr where
() expr1 expr2 = eval expr1 eval expr2
by the way:
simplify expr= Const (eval expr)
..
2009/3/13 Alberto G. Corona agocor...@gmail.com
Sorry(Const a) (Const b) = a b
also
(*) (Const a) (Const b)= Const (a*b)
2009/3/13 Alberto G. Corona agocor...@gmail.com
() :: (Ord a) = a - a - Bool
what´s the problem?
make your Expr an instance of Ord.
By the way
instance Num Expr where
fromInterger = Const
(+) = Plus
(*) = Times
does not work. you have not defined (+) and (*) for Const Integer.
(+) (Const a) (Const b)= Const (a+b)
With this you have an evaluator.
In the same way:
(Const a) (Const b) = Const (a b)
2009/3/12 Adam Vogt vogt.a...@gmail.com
This seems to be in ghc for those reasons:
http://www.haskell.org/haskellwiki/Quasiquotation
* On Monday, March 02 2009, Andrew Hunter wrote:
Several times now I've had to define an EDSL for working with
(vaguely) numeric expressions. For stuff like 2*X+Y, this is easy,
looking pretty much like:
data Expr = Const Integer | Plus Expr Expr | Times Expr Expr
instance Num Expr where
fromInterger = Const
(+) = Plus
(*) = Times
c. This lets me get a perfectly nice AST, which is what I want.
When I want to be able to express and work with inequalities and
equalities, this breaks. Suppose I want to write 2*X + Y 3. I
either have to:
a) Hide Prelude.() and define a simple that builds the AST term I
want.
b) Come up with a new symbol for it that doesn't look totally awful.
Neither of these work decently well. Hiding Eq and Ord operators,
which is what I effectively have to do for a), is pretty much a
nonstarter--we'll have to use them too much for that to be practical.
On the other hand, b) works...but is about as ugly as it gets. We
have lots and lots of symbols that are already taken for important
purposes that are syntactically near ,=,==, and the like: and
and = for monads, for arrows, etc. There...are not good
choices that I know of for the symbols that don't defeat the purpose
of making a nice clean EDSL for expressions; I might as well use 3*X +
Y `lessthan` 3, which is just not cool.
Does anyone know of a good solution, here? Are there good
substitutions for all the six operators that are important
(,,=,=,==,/=), that are close enough to be pretty-looking but not
used for other important modules?
Better yet, though a little harder, is there a nice type trick I'm not
thinking of? This works for Num methods but not for Ord methods
because:
(+) :: (Num a) = a - a - a
() :: (Ord a) = a - a - Bool
i.e. the return type of comparisons is totally fixed. I don't suppose
there's a good way to...well, I don't know what the *right* answer is,
but maybe define a new typeclass with a more flexible type for that
lets both standard types return Bool and my expressions return Expr?
Any good solution would be appreciated.
Thanks,
AHH
___
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] Re: Against cuteness
Benjamin L.Russell dekudekup...@yahoo.com wrote: balance Stop right there. Any further word about what the Taiji means would only make you look even more clueless. Take a scale if you want a symbol for balance[1]. OTOH, laziness(yin) and strictness(yang) make a far better pair of unified opposites than the schemeish eval and apply (which's outer essences are both yang, changing to yin only by means of what they execute[2]). Still, you wouldn't represent the Maybe monad with =, now would you? Instantiating a symbol for a general principle to whatever you like constitutes pocketing. Anyway, I think it's too late for logo submissions. Personally, I just love the lambda-bind, it's truly haskellish, sleek, appropriately cryptic and lends itself well to ascii-art. What about a chicken holding a curry dispenser? In any case, I don't think a sloth is a bad choice as a mascot: It's most likely the most efficient animal on earth, and seeing it, you're bound to be mystified how it manages to get anything done. Water overcomes stone: Shapeless, it requires no opening: The benefit of taking no action. Yet benefit without action, And experience without abstraction, Are practiced by very few. [1] Or the vector equilibrium (note the word libra in there): http://www.angelfire.com/mt/marksomers/91.html It's also the reason why cutting a pizza into anything else but six pieces is an abomination to geometry.[2] [2] While I'm at it: The tips of the pinky, index finger, and thumb form a tetrahedron together with the center of mass in your palm while holding such a piece. What do you make of that? [3] And are therefore better explained in terms of hodge and podge -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] DSLs with {in,}equalities
even at the level of expressions you can be sure that inequalities hold. So you can create an instance of Ord. for example: (Sum x z) y | x== y z0 = True | here x and y can be expressions and == can have its own rules with this you can compute symbolically, because you don´t need to reduce the expression to a numerical value. It´s a matter of finding rules. 2009/3/13 Alberto G. Corona agocor...@gmail.com () :: (Ord a) = a - a - Bool what´s the problem? make your Expr an instance of Ord. By the way instance Num Expr where fromInterger = Const (+) = Plus (*) = Times does not work. you have not defined (+) and (*) for Const Integer. (+) (Const a) (Const b)= Const (a+b) With this you have an evaluator. In the same way: (Const a) (Const b) = Const (a b) 2009/3/12 Adam Vogt vogt.a...@gmail.com This seems to be in ghc for those reasons: http://www.haskell.org/haskellwiki/Quasiquotation * On Monday, March 02 2009, Andrew Hunter wrote: Several times now I've had to define an EDSL for working with (vaguely) numeric expressions. For stuff like 2*X+Y, this is easy, looking pretty much like: data Expr = Const Integer | Plus Expr Expr | Times Expr Expr instance Num Expr where fromInterger = Const (+) = Plus (*) = Times c. This lets me get a perfectly nice AST, which is what I want. When I want to be able to express and work with inequalities and equalities, this breaks. Suppose I want to write 2*X + Y 3. I either have to: a) Hide Prelude.() and define a simple that builds the AST term I want. b) Come up with a new symbol for it that doesn't look totally awful. Neither of these work decently well. Hiding Eq and Ord operators, which is what I effectively have to do for a), is pretty much a nonstarter--we'll have to use them too much for that to be practical. On the other hand, b) works...but is about as ugly as it gets. We have lots and lots of symbols that are already taken for important purposes that are syntactically near ,=,==, and the like: and and = for monads, for arrows, etc. There...are not good choices that I know of for the symbols that don't defeat the purpose of making a nice clean EDSL for expressions; I might as well use 3*X + Y `lessthan` 3, which is just not cool. Does anyone know of a good solution, here? Are there good substitutions for all the six operators that are important (,,=,=,==,/=), that are close enough to be pretty-looking but not used for other important modules? Better yet, though a little harder, is there a nice type trick I'm not thinking of? This works for Num methods but not for Ord methods because: (+) :: (Num a) = a - a - a () :: (Ord a) = a - a - Bool i.e. the return type of comparisons is totally fixed. I don't suppose there's a good way to...well, I don't know what the *right* answer is, but maybe define a new typeclass with a more flexible type for that lets both standard types return Bool and my expressions return Expr? Any good solution would be appreciated. Thanks, AHH ___ 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] Does anybody dislike implicit params as much asI do?
Jules Bean wrote: Thomas Hartman wrote: http://blog.patch-tag.com/2009/03/09/implicitparams-are-evil-thoughts- on-adapting-gitit/ I understand there are arguments for using IPs, but after this experience, the ImplicitParams extension is a code smell for me. It's not just you. Implicit parameters are a scourge on the language. I think they have a useful place in propagating semi-global configuration information without imposing huge syntactic overhead. I think using them like in the code referred to in the URL above, where their values are frequently changed down the call stack, is dangerous. Ganesh === Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html === ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Against cuteness
On Thu, Mar 12, 2009 at 9:17 PM, Benjamin L. Russell dekudekup...@yahoo.com wrote: On Thu, 12 Mar 2009 09:11:15 -0500, Gregg Reynolds d...@mobileink.com wrote: I don't think so. Bad design will lose them (and many others), but good design and cuteness are two different things. It's also possible for a good design to be cute, too. De cutibus non est disputandem. Personally I think something interesting could be done with Thoth (nice open svg image at http://en.wikipedia.org/wiki/Thoth): God of reading/writing, math. When conflated with Hermes, also of boundaries, thieves and scoundrels, etc. Then there's Haskell B. Curry himself; notice the resemblance (http://www.haskell.org/bio.html) with J. R. Bob Dobbs (http://en.wikipedia.org/wiki/J._R._%22Bob%22_Dobbs). An artist could comicize an image of Curry. Then it's only a short step to actual cultdom - why stop with a mere web community when you can legally establish a religious cult and actually ordain Ministers? (http://www.subgenius.com/scatalog/membership.htm). -g ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Sugestion for a Haskell mascot
I've unconciously conditioned myself to think about rabbits with nukes each time I think about monads. Warm fuzzy things launching the missiles indeed. On Friday 13 March 2009 02.38.29 Richard O'Keefe wrote: On 12 Mar 2009, at 11:08 pm, Satnam Singh wrote: I agree that looking for a mascot that is inspired by laziness is a bad idea from a P.R. perspective (I am tired of people walking out the room when I give Haskell talks to general audiences and explain lazy evaluation). Perhaps we should call it Just-In-Time evaluation. As for mascots, let's take a photo of Simon Peyton Jones, shrink him to hobbit size, give him furry feet, and announce that here is one of the warm fuzzy things we have in mind when we use monads. (:-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Sjur Gjøstein Karevoll sjurberen...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Applicative combinators from Parsec
Hello, Looking at Parsec 3 I see: chainr1 :: (Stream s m t) = ParsecT s u m a - ParsecT s u m (a - a - a) - ParsecT s u m a chainr1 p op = scan where scan = do x - p; rest x rest x = (do f - op; y - scan; return (f x y)) | return x But if I remove the type signature and let GHC infer it for me, I get a much more generic type: chainr1 :: (Alternative m, Monad m) = m a - m (a - a - a) - m a But we don't really need m to be a monad since we're only doing applicative operations, so after some rewriting we get: chainr1 :: Alternative f = f a - f (a - a - a) - f a chainr1 p op = scan where scan = flip id $ p * rest rest = (flip $ op * scan) | pure id Would it be a good idea to: 1) make the Parsec combinators as generic as possible and 2) move the really generic applicative ones to Control.Applicative? Thanks, Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Against cuteness
On Fri, 13 Mar 2009 12:29:25 +0100, Achim Schneider bars...@web.de wrote: Benjamin L.Russell dekudekup...@yahoo.com wrote: balance Stop right there. Any further word about what the Taiji means would only make you look even more clueless. Take a scale if you want a symbol for balance[1]. Granted, I'm no expert on Taoism, so I am not qualified to comment on the meaning of the Taiji. Rather, I was merely trying to assign meaning to a symbol that resembled the Taiji, but not to interpret the Taiji itself. OTOH, laziness(yin) and strictness(yang) make a far better pair of unified opposites than the schemeish eval and apply (which's outer essences are both yang, changing to yin only by means of what they execute[2]). Indeed. But strictness would not characterize Haskell, would it? Still, you wouldn't represent the Maybe monad with =, now would you? Instantiating a symbol for a general principle to whatever you like constitutes pocketing. Indeed. The symbol would need to be modified and distinguished appropriately. Anyway, I think it's too late for logo submissions. Personally, I just love the lambda-bind, it's truly haskellish, sleek, appropriately cryptic and lends itself well to ascii-art. Agreed. What about a chicken holding a curry dispenser? In any case, I don't think a sloth is a bad choice as a mascot: It's most likely the most efficient animal on earth, and seeing it, you're bound to be mystified how it manages to get anything done. It's indeed efficient, but also slow; while Schemers are accused of knowing the value of everything, but the cost of nothing, a sloth mascot could cause Haskellers to become accused of knowing the efficiency of everything, but the speed of nothing, no? Water overcomes stone: Shapeless, it requires no opening: The benefit of taking no action. Yet benefit without action, And experience without abstraction, Are practiced by very few. Nice poem. Did you write it yourself, or can you document the source? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Against cuteness
Hallo, On Fri, Mar 13, 2009 at 1:23 PM, Benjamin L. Russell dekudekup...@yahoo.com wrote: On Fri, 13 Mar 2009 12:29:25 +0100, Achim Schneider bars...@web.de Water overcomes stone: Shapeless, it requires no opening: The benefit of taking no action. Yet benefit without action, And experience without abstraction, Are practiced by very few. Nice poem. Did you write it yourself, or can you document the source? If I remember correctly, this is from the Daodejing. Cheers, -- -alex http://www.ventonegro.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Applicative combinators from Parsec
2009/3/13 Martijn van Steenbergen mart...@van.steenbergen.nl: Hello, Looking at Parsec 3 I see: chainr1 :: (Stream s m t) = ParsecT s u m a - ParsecT s u m (a - a - a) - ParsecT s u m a chainr1 p op = scan where scan = do x - p; rest x rest x = (do f - op; y - scan; return (f x y)) | return x But if I remove the type signature and let GHC infer it for me, I get a much more generic type: chainr1 :: (Alternative m, Monad m) = m a - m (a - a - a) - m a But we don't really need m to be a monad since we're only doing applicative operations, so after some rewriting we get: chainr1 :: Alternative f = f a - f (a - a - a) - f a chainr1 p op = scan where scan = flip id $ p * rest rest = (flip $ op * scan) | pure id Would it be a good idea to: 1) make the Parsec combinators as generic as possible and 2) move the really generic applicative ones to Control.Applicative? Thanks, Martijn. This reminds me of something similar I find a bit annoying: There are some functions like (|) which are defined separately in Text.Parsec and Control.Applicative, meaning that you have to hide one of the sets. Would it be better perhaps to just have Parsec reexport the existing functions from Applicative, or something like that? (Currently the functions in Parsec have the more specific type as Martijn says, but if they're generalised then I don't really see why they need to be duplicated.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
Don Stewart ha scritto: [...] I think uvector only works with certain types that can be unboxed, while storablevector works with all types that instantiate Foreign.Storable.Storable. I don't know about vector. From the description of vector, I have the One of the nice feature of uvector is the support for UArr (a :*: b). An UArr (a :*: b) can be easily (with fstU and sndU) transformed in UArr a and UArr b. uvector package also suppors Complex and Rational, however the support for these type is hard written, using a UAProd class, and requires some boiler plate code (IMHO). I find StorableVector implementation much more simple; I would like to see it in the Haskell Platform. As for Data.Parallel, uvector and vector, it seems there is some code duplication. Both Data.Parallel and uvector, make us of a strict pair type. Such a type is also implemented in the strict package [1]. The authors are the same, so I don't understand the reason of code replication. There is also replication in the definition of the Stream data type. [1] there seems to be an error in the documentation: http://hackage.haskell.org/packages/archive/strict/0.3.2/doc/html/Data-Strict-Tuple.html In the description, there is: Same as regular Haskell pairs, but (x :*: _|_) = (_|_ :*: y) = _|_ but in the synopsis, the data constructor is :!:, not :*:. Regards Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Sugestion for a Haskell mascot
What about the Rabbit of Caerbannog[1]. Looks cute on first sight, but upon further investigation turns out to be a vicious killer. Useful to quench any rumors of Haskell being a toy language. You just need to look a bit closer. [1] http://en.wikipedia.org/wiki/Rabbit_of_Caerbannog On Fri, Mar 13, 2009 at 1:29 PM, Sjur Gjøstein Karevoll sjurberen...@gmail.com wrote: I've unconciously conditioned myself to think about rabbits with nukes each time I think about monads. Warm fuzzy things launching the missiles indeed. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Pointless functors
Bonjour café, Are there any functors f for which no point/pure/return :: a - f a exists? Thank you, Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
Don Stewart ha scritto: bulat.ziganshin: Hello Don, Wednesday, March 11, 2009, 12:12:07 AM, you wrote: Right, so my point stands: there's no difference now. If you can write a Storable instance, you can write a UA et al instance. yes, if there is some class provided for this and not just hard-coded 4 or so base types That's right. For example (supporting even pairs): instance (RealFloat a, UA a) = UA (Complex a) where newtype UArr (Complex a) = UAComplex (UArr (a :*: a)) newtype MUArr (Complex a) s = MUAComplex (MUArr (a :*: a) s) You also have to add instance for UIO: instance (RealFloat a, UIO a) = UIO (Complex a) where hPutU h (UAComplex arr) = hPutU h arr hGetU h = do arr - hGetU h return (UAComplex arr) With Storable, this should not be required; you just have to write an instance for the Storable class. Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Vim support for cabal
Hi café ! I googled for some kind of vim support for cabal but found nothing. I mean syntax highlighting of .cabal and probably integration with haskellmode. Did anyone hear about such thing? Pavel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Against cuteness
Benjamin L.Russell dekudekup...@yahoo.com wrote: OTOH, laziness(yin) and strictness(yang) make a far better pair of unified opposites than the schemeish eval and apply (which's outer essences are both yang, changing to yin only by means of what they execute[2]). Indeed. But strictness would not characterize Haskell, would it? Not by itself, no. But Haskell, as a language that's neither strict nor lazy, but non-strict (and can therefore combine eagerness and laziness) is closer to the Tao of execution than any purely strict or purely lazy language. One, after all, cannot be without the other: Both are not separate, but distinguished only by our perception. What about a chicken holding a curry dispenser? In any case, I don't think a sloth is a bad choice as a mascot: It's most likely the most efficient animal on earth, and seeing it, you're bound to be mystified how it manages to get anything done. It's indeed efficient, but also slow; while Schemers are accused of knowing the value of everything, but the cost of nothing, a sloth mascot could cause Haskellers to become accused of knowing the efficiency of everything, but the speed of nothing, no? I'd say we know the necessity of everything, but the schedule of nothing. ...the point I'm trying to make here is that the appearance of swiftness is not everything: A tight loop executing nop's may seem busy, but won't tell you much interesting stuff. Imagine a cute sloth peeking out of a PC case, together with Lazy bum is executeing ur prugram, but only half of it Water overcomes stone: Shapeless, it requires no opening: The benefit of taking no action. Yet benefit without action, And experience without abstraction, Are practiced by very few. Nice poem. Did you write it yourself, or can you document the source? It's out of the Tao te Ching, by, allegedly, Lao Tzu. It hints at Wuwei[1], or, from another angle, Kant's Categorical Imperative. [1]http://en.wikipedia.org/wiki/Wu_wei -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Sugestion for a Haskell mascot
Roel van Dijk vandijk.r...@gmail.com wrote: What about the Rabbit of Caerbannog[1]. Looks cute on first sight, but upon further investigation turns out to be a vicious killer. Useful to quench any rumors of Haskell being a toy language. You just need to look a bit closer. [1] http://en.wikipedia.org/wiki/Rabbit_of_Caerbannog Is that, in some way, connected to those cute christmas critters Erik [afair] thought of that keep creeping the hell out of everyone in Imaginationland? (I guess I watched too much Southpark) -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined 2009/3/13 Ross Paterson r...@soi.city.ac.uk: On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
Manlio Perillo ha scritto: [...] uvector package also suppors Complex and Rational, however the support for these type is hard written, using a UAProd class, and requires some boiler plate code (IMHO). Correction: UAProd is not a class, sorry. It is the UA constructor overloaded for a:*:b, and Complex and Rational just reuse this specialization. [...] Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On 13 Mar 2009, at 14:32, Ross Paterson wrote: On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape Correspondingly, consider the functor Const Void. Cheers Conor ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Dynamically typing TH.Exp at runtime
On 2009 Mar 13, at 4:03, Martin Hofmann wrote: That's true, inferring the type of a string is not the problem. However, I am not only interested in the top-level type, but also in the type of any arbitrary subexpression. Consider for example following recursive definition: I'm pretty sure you can pull a typed AST out of ghc-api and query the type of any node. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Fri, Mar 13, 2009 at 02:32:23PM +, Ross Paterson wrote: On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape But since f may be polymorphic in some other types, it may not be possible to choose such an arbitrary shape. For example, ((,) w) is a Functor but it is not possible to define a function point :: a - (w,a) without (1) using undefined for the value of type w, or (2) putting some sort of constraint on w which lets us choose a canonical value of type w, such as Monoid. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Vintage BASIC 1.0
On Fri, Mar 13, 2009 at 1:31 AM, Wolfgang Jeltsch jelt...@informatik.tu-cottbus.de wrote: When running the executable, nothing happens. The executable should show a usage message instead. Where are the BASIC programs? I think, you have to grab them from the source. They should be installed, too. Thanks for your feedback, and for checking out Vintage BASIC! I will add a usage message, as you suggested. Currently the usage is only described in the User's Guide. There are no options; you just give it the name of one or more BASIC source files. (Naturally this extends to doing nothing when supplied with zero source files.) The BASIC games are at http://www.vintage-basic.net/games.html. There is a tarball of all the games (bcg.tar.gzhttp://www.vintage-basic.net/downloads/bcg.tar.gz) as well. These are separated from the Vintage BASIC distribution for legal reasons. Vintage BASIC is copyrighted by me under a BSD license. The games were written by many authors and compiled into a book copyrighted by Creative Computing. I have secured permission from the editor to post the games. I do not wish to imply that they are covered by the same license as the interpreter. If anyone has any suggestions as to how to make the process simpler, I'd be happy to hear it. Thanks, Lyle P.S. I need to get my other e-mail account subscribed to this list ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
Eugene Kirpichov wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined Prelude fmap (const True) undefined :: [Bool] *** Exception: Prelude.undefined Or is that not what you mean? Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Fri, Mar 13, 2009 at 05:35:31PM +0300, Eugene Kirpichov wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined This is false. Prelude fmap (const 1) [()] [1] Prelude fmap (const 1) undefined *** Exception: Prelude.undefined -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Natural Numbers: Best implementation?
On 2009 Mar 13, at 4:25, Wolfgang Jeltsch wrote: Am Freitag, 13. März 2009 04:53 schrieb Brandon S. Allbery KF8NH: On 2009 Mar 12, at 22:54, Mark Spezzano wrote: I was wondering what the best way to implement Natural number would be. Is there a package which already does this? type-level on Hackage. I think, the original poster wanted value-level naturals, not type- level naturals. My (possibly incorrect) understanding was that value-level naturals required runtime range checks, whereas type-level naturals allowed you to validate them at compile time. I thought I'd mentioned that in my response, contrasting type-level naturals with value-level newtypes and other implementations. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Applicative combinators from Parsec
On 2009 Mar 13, at 9:57, andy morris wrote:
(Currently the functions in Parsec have the more specific type as
Martijn says, but if they're generalised then I don't really see why
they need to be duplicated.)
Possibly so Parsec has decent performance on Haskell compilers that
don't do {-# SPECIALIZE #-}?
--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com
system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
electrical and computer engineering, carnegie mellon universityKF8NH
PGP.sig
Description: This is a digitally signed message part
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
For most functors, that is equivalent to point x = undefined But by that logic, everything is a member of every typeclass... -- Robin On Fri, 13 Mar 2009 17:35:31 +0300 Eugene Kirpichov ekirpic...@gmail.com wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined 2009/3/13 Ross Paterson r...@soi.city.ac.uk: On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape ___ 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] Pointless functors
On Fri, 13 Mar 2009 14:32:23 + Ross Paterson r...@soi.city.ac.uk wrote: On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen wrote: Are there any functors f for which no point/pure/return :: a - f a exists? No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape This suggests a fun way to define a monad for a functor F: -- Does nothing, has no effect, and returns () noOp :: F () noOp = ... instance Monad F where return x = fmap (const x) noOp (=) f x = ... I think noOp would be a nice addition to the Monad class, as well. -- Robin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
Well, yes; then, that means that an arbitrary element is also false: you can't just take an arbitrary element and hope that works well. Then the original question must be reformulated: - Are there any functors for which there exists at least one non-bottom value of type 'f a' for some a, but there does not exist a function point :: a - f a such that (a != _|_) = (point a != _|_). 2009/3/13 Brent Yorgey byor...@seas.upenn.edu: On Fri, Mar 13, 2009 at 05:35:31PM +0300, Eugene Kirpichov wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined This is false. Prelude fmap (const 1) [()] [1] Prelude fmap (const 1) undefined *** Exception: Prelude.undefined -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov Web IR developer, market.yandex.ru ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using a monad to decompose a function into functions
2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: ... Threading the state is not the problem. Maybe this will help: what I have now: fsm world state = case state of first - do_stuff_one (move_up, succ state) second - do_stuff_two (move_left, succ state) third - do_stuff_three (move_right, first) what I'd want to have is to say: fsm world state = do do_stuff_one yield move_up do_stuff_two yield move_left do_stuff_three yield move_right fsm world state and have it translated to: fsm world state = do_stuff_one (move_up, \world' state' - do_stuff_two (move_left, \world'' state'' - do_stuff_three (move_right, fsm world'' state'') Hi, I've not fully understood your exact problem but I think you might have a look to Continuations and Delimited Continuations. Both can help you solve the problem with implementing a yield statement. You can have a look at one of my (rather) old blog's posts about how to implement yield/send statements a-la-python: http://monadicheadaches.blogspot.com/2008/01/python-25s-iterators-in-haskell-sort-of.html Notice that blogspot messed up with code blocks so indentation looks bad and some character is even missing. Bye, Cristiano ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Thursday 12 March 2009 10:30:47 pm Robin Green wrote:
For most functors, that is equivalent to
point x = undefined
But by that logic, everything is a member of every typeclass...
There are some cases where expected laws will prevent that. For instance, If
you try to make a monad like:
instance Monad m where
return = undefined
m = f = undefined
Then it will fail the law:
m = return = m
unless the only possible value of m is undefined (that is, m a is uninhabited
except for bottom).
In the case of pointed functors, the point is supposed to be a natural
transformation from the identity functor to the functor in question, so:
fmap f . point = point . f
which always works with 'point = undefined' as long as 'fmap f' is strict
(which it's basically required to be, since it must satisfy fmap id = id, and
id is strict).
Of course, the fact that it satisfies the relevant law doesn't make it less
worthless as an instance. To make things less trivial, one might restrict
himself to definitions that would work in a total language, and then it's easy
to come up with examples of functors that aren't pointed. For instance, one
can write the following in Agda:
data Void (a : Set) : Set where -- empty
mapVoid : {a b : Set} - (a - b) - Void a - Void b
mapVoid f () -- empty function
pointVoid : {a : Set} - a - Void a
pointVoid = ? -- can't be written
-- Dan
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Fri, Mar 13, 2009 at 04:11:57PM +0100, Martijn van Steenbergen wrote: Eugene Kirpichov wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined Prelude fmap (const True) undefined :: [Bool] *** Exception: Prelude.undefined Or is that not what you mean? OK, an arbitrary maximal element. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to get a typed (type tagged) AST from GHC's core [Was: Dynamically typing TH.Exp at runtime]
Brandon S. Allbery KF8NH wrote: I'm pretty sure you can pull a typed AST out of ghc-api and query the type of any node. Thanks. I am relieved to hear that. Could anybody tell me, where to start in the ghc-api? It's pretty hard, when you don't know where to look. Hoogle doesn't know anything about it. I found following DT describing the core language, but as far as I see, there are no type in there either. http://www.haskell.org/ghc/docs/latest/html/libraries/ghc/CoreSyn.html#t %3AExpr Thanks a lot, Martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
Ross Paterson wrote: No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape Interesting. Is the arbitrariness of the shape some sort of evidence that Pointed is not really a very useful class in its own right? Certainly, the shape does matter if you plan to progress to non-trivial Applicative or Monad instances. For example, the non-determinism monad requires shape = [()], while the ZipList applicative functor requires shape = repeat (). Eugene Kirpichov wrote: 'An arbitrary element' means 'undefined will suffice' point x = fmap (const x) undefined Well, that would rather limit the possible Applicative instances. :-) (Consider the Applicative law: fmap g x = pure g * x) Brent Yorgey wrote: Prelude fmap (const 1) [()] [1] Prelude fmap (const 1) undefined *** Exception: Prelude.undefined True, but as far as I can tell, that doesn't violate any laws of the Pointed class. To put it crudely, if [] is as good as [()], then how is undefined any worse? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Sat, 2009-03-14 at 02:12 +1000, Matthew Brecknell wrote: Ross Paterson wrote: No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape Interesting. Is the arbitrariness of the shape some sort of evidence that Pointed is not really a very useful class in its own right? A simpler bit of evidence is that the only law I can think of for point (in its own right) is fmap f . point = point . f which we get free anyway. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pointless functors
On Sat, Mar 14, 2009 at 02:12:45AM +1000, Matthew Brecknell wrote: Ross Paterson wrote: No. Choose an arbitrary element shape :: f () and define point x = fmap (const x) shape Interesting. Is the arbitrariness of the shape some sort of evidence that Pointed is not really a very useful class in its own right? Not useless, but equivalent to class Functor f = Pointed f where unit :: f () Naturality of point does the rest. But not all definitions of unit are equally useful. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
manlio_perillo: Don Stewart ha scritto: bulat.ziganshin: Hello Don, Wednesday, March 11, 2009, 12:12:07 AM, you wrote: Right, so my point stands: there's no difference now. If you can write a Storable instance, you can write a UA et al instance. yes, if there is some class provided for this and not just hard-coded 4 or so base types That's right. For example (supporting even pairs): instance (RealFloat a, UA a) = UA (Complex a) where newtype UArr (Complex a) = UAComplex (UArr (a :*: a)) newtype MUArr (Complex a) s = MUAComplex (MUArr (a :*: a) s) You also have to add instance for UIO: instance (RealFloat a, UIO a) = UIO (Complex a) where hPutU h (UAComplex arr) = hPutU h arr hGetU h = do arr - hGetU h return (UAComplex arr) With Storable, this should not be required; you just have to write an instance for the Storable class. Though you get no IO operations with Storable... UIO is entirely separate. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Combining haddock documentation from multiple packages
Is it possible to generate a unified documentation tree similar to http://www.haskell.org/ghc/docs/latest/html/libraries/index.html from packages installed via cabal from hackage? And if so, how does one go about doing it? -- Heikki Aitakangas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using a monad to decompose a function into functions
On Friday 13 March 2009, Cristiano Paris wrote: 2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: ... Threading the state is not the problem. Maybe this will help: what I have now: fsm world state = case state of first - do_stuff_one (move_up, succ state) second - do_stuff_two (move_left, succ state) third - do_stuff_three (move_right, first) what I'd want to have is to say: fsm world state = do do_stuff_one yield move_up do_stuff_two yield move_left do_stuff_three yield move_right fsm world state and have it translated to: fsm world state = do_stuff_one (move_up, \world' state' - do_stuff_two (move_left, \world'' state'' - do_stuff_three (move_right, fsm world'' state'') Hi, I've not fully understood your exact problem but I think you might have a look to Continuations and Delimited Continuations. Both can help you solve the problem with implementing a yield statement. You can have a look at one of my (rather) old blog's posts about how to implement yield/send statements a-la-python: http://monadicheadaches.blogspot.com/2008/01/python-25s-iterators-in-haskel l-sort-of.html Notice that blogspot messed up with code blocks so indentation looks bad and some character is even missing. Hi, I've already checked those out. I tried using your yield implementation and while it works, I couldn't get it to work with the state monad. So while: data RecPair a b = Nil | RP (b, a - RecPair a b) yield x = Cont $ \k - RP (x, k) got me half-way to my goal, I couldn't figure out how to make something like: yield' = do state - get state' - yield state put state' Thanks! Marcin Kosiba signature.asc Description: This is a digitally signed message part. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to get a typed (type tagged) AST from GHC's core [Was: Dynamically typing TH.Exp at runtime]
Hi Martin, Could anybody tell me, where to start in the ghc-api? It's pretty hard, when you don't know where to look. Hoogle doesn't know anything about it. I found following DT describing the core language, but as far as I see, there are no type in there either. I've been working on parsing core in the past few months. For an example, look here: http://git.stderr.nl/gitweb?p=matthijs/projects/fhdl.git;a=blob;f=Translator.hs;h=8072f85925ad1238 The loadModule and findBind functions are interesting. As for iterating the AST, have a look at Flatten.hs. Good luck, any questions are welcome! Gr. Matthijs signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
Don Stewart ha scritto: [...] You also have to add instance for UIO: instance (RealFloat a, UIO a) = UIO (Complex a) where hPutU h (UAComplex arr) = hPutU h arr hGetU h = do arr - hGetU h return (UAComplex arr) With Storable, this should not be required; you just have to write an instance for the Storable class. Though you get no IO operations with Storable... UIO is entirely separate. Yes, but using Storable and Foreign.Ptr, IO is rather simple. From storablevector package: -- | Outputs a 'Vector' to the specified 'Handle'. hPut :: (Storable a) = Handle - Vector a - IO () hPut h v = if null v then return () else let (fptr, s, l) = toForeignPtr v in withForeignPtr fptr $ \ ptr - let ptrS = advancePtr ptr s ptrE = advancePtr ptrS l -- use advancePtr and minusPtr in order to respect -- alignment in hPutBuf h ptrS (minusPtr ptrE ptrS) -- | Read a 'Vector' directly from the specified 'Handle'. This -- is far more efficient than reading the characters into a list -- and then using 'pack'. -- hGet :: (Storable a) = Handle - Int - IO (Vector a) hGet _ 0 = return empty hGet h i = createAndTrim i $ \p - let elemType :: Ptr a - a elemType _ = undefined sizeOfElem = sizeOf (elemType p) in fmap (flip div sizeOfElem) $ hGetBuf h p (i * sizeOfElem) Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
Bryan O'Sullivan ha scritto: [...] text is not mature, and is based on the same modern fusion framework as uvector and vector. It uses unpinned arrays, but provides functions for dealing with foreign code. What is the reason why you have decided to use unpinned arrays (ByteArray#) instead of pinned arrays (Foreign.Ptr)? [...] Thanks Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
manlio_perillo: Bryan O'Sullivan ha scritto: [...] text is not mature, and is based on the same modern fusion framework as uvector and vector. It uses unpinned arrays, but provides functions for dealing with foreign code. What is the reason why you have decided to use unpinned arrays (ByteArray#) instead of pinned arrays (Foreign.Ptr)? They prevent heap fragmentation (and in general are faster). -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Has anybody replicated =~ s/../../ or even something more basic for doing replacements with pcre haskell regexen?
tphyahoo: Is there something like subRegex... something like =~ s/.../.../ in perl... for haskell pcre Regexen? I mean, subRegex from Text.Regex of course: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/regex-compat Thanks for any advice, Basically, we should have it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using a monad to decompose a function into functions
2009/3/13 Marcin Kosiba marcin.kos...@gmail.com:
Threading the state is not the problem. Maybe this will help:
what I have now:
fsm world state = case state of
first -
do_stuff_one
(move_up, succ state)
second -
do_stuff_two
(move_left, succ state)
third -
do_stuff_three
(move_right, first)
what I'd want to have is to say:
fsm world state = do
do_stuff_one
yield move_up
do_stuff_two
yield move_left
do_stuff_three
yield move_right
fsm world state
and have it translated to:
fsm world state =
do_stuff_one
(move_up, \world' state' -
do_stuff_two
(move_left, \world'' state'' -
do_stuff_three
(move_right, fsm world'' state'')
Do you really need yield? Most of the time, you should be able to
implement move_up and the rest directly using bits of the run
function.
But assuming you do need yield, you probably want a resumption monad.
Here's a variant of an implementation I've worked with recently.
data Thunk r m a = Val a | Suspend r (m (Thunk r m a))
newtype Suspend r m a = C { unC :: forall b. (a - m (Thunk r m a)) -
m (Thunk r m a) }
instance Monad (Suspend r m) where
return a = C (\k - k a)
m = f = C (\k - unC m (\a - unC (f a) k))
instance MonadTrans (Suspend r) where
lift m = C (\k - m = k)
suspend :: Monad m = r - Suspend r m ()
suspend r = C (\k - return $ Suspend r (k ()))
run :: Monad m = Suspend r m a - m (Thunk r m a)
run m = unC m (return . Val)
These laws should give an idea of how it works:
run (return a) = return (Val a)
run (lift m = f) = m = \a - run (f a)
run (suspend r m) = return (Suspend r (run m))
There's also a function that undoes run, although you shouldn't need it.
enter :: Monad m = Thunk r m a - Suspend r m a
enter (Val a) = return a
enter (Suspend r m) = suspend r lift m = enter
--
Dave Menendez d...@zednenem.com
http://www.eyrie.org/~zednenem/
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] bytestring vs. uvector
Hello Don, Friday, March 13, 2009, 8:08:57 PM, you wrote: What is the reason why you have decided to use unpinned arrays (ByteArray#) instead of pinned arrays (Foreign.Ptr)? They prevent heap fragmentation (and in general are faster). you probably mean faster alloc/gc operations, everything else should be the same -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Vim support for cabal
2009/3/13 Pavel Perikov peri...@gmail.com: Hi café ! I googled for some kind of vim support for cabal but found nothing. I mean syntax highlighting of .cabal and probably integration with haskellmode. Did anyone hear about such thing? Pavel I've been wanting something like this as well, so you inspired me to finally get round to writing it. :D I've stuck it on Patch-tag, so: darcs get http://patch-tag.com/publicrepos/cabal-vim Nothing special at the moment; it just highlights field names and does some basic autoindenting. If you (or someone else on the list) have any suggestions, then just say (or send a patch if you want :) ) I might add to it over the weekend as well (highlighting of compiler names in the 'tested-on' field, that sort of thing), so perhaps check back in a few days. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] broken IO support in uvector package, when using non primitive types
Hi. I'm sure this is a know bug, but I can't find details with Google. The offending code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2362 When I execute the program I get: uio: readChunkBU: can't read What's the problem? I'm using uvector from: http://code.haskell.org/~dons/code/uvector/ Thanks Manlio Perillo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
Am Freitag, 13. März 2009 21:18 schrieb Manlio Perillo: Hi. I'm sure this is a know bug, but I can't find details with Google. The offending code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2362 When I execute the program I get: uio: readChunkBU: can't read What's the problem? I'm using uvector from: http://code.haskell.org/~dons/code/uvector/ Thanks Manlio Perillo Worked with uvector-0.1.0.1: $ ghc --make readUArr.hs [1 of 1] Compiling Main ( readUArr.hs, readUArr.o ) Linking readUArr ... $ ./readUArr 2 But not with uvector-0.2 $ ./readUArr readUArr: readChunkBU: can't read ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
As far as I know, the reason for this is that the UIO instance for productions writes the two rows out sequentially to file, but doesn't include any means to determine the length of the two halves when it's loading up again. When you try to read the production back in, it tries to read in two arrays, but the first array read consumes all the input leaving the second with nothing. Having said that, I'm not sure why it used to work. I remember testing this on the version in hackage and finding the same issue. Cheers, Dan On Fri, Mar 13, 2009 at 4:46 PM, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Freitag, 13. März 2009 21:18 schrieb Manlio Perillo: Hi. I'm sure this is a know bug, but I can't find details with Google. The offending code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2362 When I execute the program I get: uio: readChunkBU: can't read What's the problem? I'm using uvector from: http://code.haskell.org/~dons/code/uvector/ Thanks Manlio Perillo Worked with uvector-0.1.0.1: $ ghc --make readUArr.hs [1 of 1] Compiling Main ( readUArr.hs, readUArr.o ) Linking readUArr ... $ ./readUArr 2 But not with uvector-0.2 $ ./readUArr readUArr: readChunkBU: can't read ___ 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] broken IO support in uvector package, when using non primitive types
UIO's also only a truly alpha idea as a proxy for bytestring/Binary support. Patches welcome. pumpkingod: As far as I know, the reason for this is that the UIO instance for productions writes the two rows out sequentially to file, but doesn't include any means to determine the length of the two halves when it's loading up again. When you try to read the production back in, it tries to read in two arrays, but the first array read consumes all the input leaving the second with nothing. Having said that, I'm not sure why it used to work. I remember testing this on the version in hackage and finding the same issue. Cheers, Dan On Fri, Mar 13, 2009 at 4:46 PM, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Freitag, 13. März 2009 21:18 schrieb Manlio Perillo: Hi. I'm sure this is a know bug, but I can't find details with Google. The offending code is here: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2362 When I execute the program I get: uio: readChunkBU: can't read What's the problem? I'm using uvector from: http://code.haskell.org/~dons/code/uvector/ Thanks Manlio Perillo Worked with uvector-0.1.0.1: $ ghc --make readUArr.hs [1 of 1] Compiling Main ( readUArr.hs, readUArr.o ) Linking readUArr ... $ ./readUArr 2 But not with uvector-0.2 $ ./readUArr readUArr: readChunkBU: can't read ___ 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] Using a monad to decompose a function into functions
2009/3/13 Marcin Kosiba marcin.kos...@gmail.com: Hi, I've already checked those out. I tried using your yield implementation and while it works, I couldn't get it to work with the state monad. So while: data RecPair a b = Nil | RP (b, a - RecPair a b) yield x = Cont $ \k - RP (x, k) got me half-way to my goal, I couldn't figure out how to make something like: yield' = do state - get state' - yield state put state' Basically, the yield is built upon the Cont monad which has a transformer counter part, ContT. You could try and re-implement the yield under ContT instead of just Cont then you can stack ContT on top of State (or StateT if you need more monads) and have a state (i.e. get/put) and the yield. Hope this helps. Cristiano ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
Daniel Peebles ha scritto: As far as I know, the reason for this is that the UIO instance for productions writes the two rows out sequentially to file, but doesn't include any means to determine the length of the two halves when it's loading up again. When you try to read the production back in, it tries to read in two arrays, but the first array read consumes all the input leaving the second with nothing. Ok, thanks. For now, I think that the simple solution is to not use UArr (a:*:b), but (UArr a, UArr b). Or I should just switch to Data.Array.Unboxed. The operations I need with the array are only: - sum of elements - binary search - serialization/deserialization - sorting (but right now I sort the list before creating the array) with a very big data set. For my problem, is uvector the best solution? What about storablevector or cvector, instead? Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
As far as I know, the reason for this is that the UIO instance for productions writes the two rows out sequentially to file, but doesn't include any means to determine the length of the two halves when it's loading up again. When you try to read the production back in, it tries to read in two arrays, but the first array read consumes all the input leaving the second with nothing. Ok, thanks. For now, I think that the simple solution is to not use UArr (a:*:b), but (UArr a, UArr b). Just newtype your own UIO instance, if you need a different instance... -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
Daniel Fischer ha scritto: [...] Worked with uvector-0.1.0.1: [...] But not with uvector-0.2 [...] The main difference is that in uvector 0.2, hPutBU does not write in the file the length of the array; hGetBU simply use the file size. let elemSize = sizeBU 1 (undefined :: e) n - fmap ((`div`elemSize) . fromInteger) $ hFileSize h So, the problem seems to be here. This simply don't support having two arrays written in the same file, and sizeBU belongs to the UAE class, whose instances are only declared for builtin types. So, the patch is: just revert this change. Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
manlio_perillo: Daniel Fischer ha scritto: [...] Worked with uvector-0.1.0.1: [...] But not with uvector-0.2 [...] The main difference is that in uvector 0.2, hPutBU does not write in the file the length of the array; hGetBU simply use the file size. let elemSize = sizeBU 1 (undefined :: e) n - fmap ((`div`elemSize) . fromInteger) $ hFileSize h So, the problem seems to be here. This simply don't support having two arrays written in the same file, and sizeBU belongs to the UAE class, whose instances are only declared for builtin types. So, the patch is: just revert this change. Or... use your own UIO instance. That's why it's a type class! Anyway, for the background on this: Tue Nov 18 08:44:46 PST 2008 Malcolm Wallace * Use hFileSize to determine arraysize, rather than encoding it in the file. Here is a patch to the uvector library that fixes hGetBU and hPutBU to use the filesize to determine arraysize, rather than encoding it within the file. I guess the disadvantages are that now only one array can live in a file, and the given Handle must indeed be a file, not a socket Handle. But the advantage is that one can read packed raw datafiles obtained externally. Still, again, I'd point out that uvector is alpha, APIs can and will change. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
Don Stewart ha scritto: [...] So, the patch is: just revert this change. Or... use your own UIO instance. That's why it's a type class! Why should I rewrite the UIO instance, if one already exists? Anyway, for the background on this: Tue Nov 18 08:44:46 PST 2008 Malcolm Wallace * Use hFileSize to determine arraysize, rather than encoding it in the file. Here is a patch to the uvector library that fixes hGetBU and hPutBU to use the filesize to determine arraysize, rather than encoding it within the file. I guess the disadvantages are that now only one array can live in a file, and the given Handle must indeed be a file, not a socket Handle. But the advantage is that one can read packed raw datafiles obtained externally. Still, again, I'd point out that uvector is alpha, APIs can and will change. Ok, with API changes. But they *should not* break normal package usage. That patch simply introduced a bug in uvector. If you think that the patch is useful, then the patch should also include a modification to the UIO instance for a:*:b. Regards Manlio ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
Am Freitag, 13. März 2009 23:53 schrieb Don Stewart:
manlio_perillo:
Daniel Fischer ha scritto:
[...]
Worked with uvector-0.1.0.1:
[...]
But not with uvector-0.2
[...]
The main difference is that in uvector 0.2, hPutBU does not write in the
file the length of the array; hGetBU simply use the file size.
let elemSize = sizeBU 1 (undefined :: e)
n - fmap ((`div`elemSize) . fromInteger) $ hFileSize h
So, the problem seems to be here.
This simply don't support having two arrays written in the same file,
and sizeBU belongs to the UAE class, whose instances are only declared
for builtin types.
So, the patch is: just revert this change.
Or... use your own UIO instance. That's why it's a type class!
Anyway, for the background on this:
Tue Nov 18 08:44:46 PST 2008 Malcolm Wallace
* Use hFileSize to determine arraysize, rather than encoding it in
the file.
Here is a patch to the uvector library that fixes hGetBU and hPutBU to
use the filesize to determine arraysize, rather than encoding it within
the file. I guess the disadvantages are that now only one array can
live in a file, and the given Handle must indeed be a file, not a
socket Handle. But the advantage is that one can read packed raw datafiles
obtained externally.
Still, again, I'd point out that uvector is alpha, APIs can and will
change.
-- Don
Though I don't really know whether what I did is sane, I can offer a few
patches which seem to work.
Check for sanity before applying :)
hunk ./Data/Array/Vector/Prim/BUArr.hs 85
- hPutBU, hGetBU
+ hPutBU, hGetBU, hGetLengthBU
hunk ./Data/Array/Vector/Prim/BUArr.hs 864
+hGetLengthBU :: forall e. UAE e = Int - Handle - IO (BUArr e)
+hGetLengthBU numEntries h =
+ do
+marr@(MBUArr _ marr#) - stToIO (newMBU numEntries)
+let bytes = sizeBU numEntries (undefined :: e)
+wantReadableHandle hGetBU h $
+\han...@handle__{ haFD=fd, haBuffer=ref, haIsStream=is_stream } - do
+ b...@buffer { bufBuf = raw, bufWPtr = w, bufRPtr = r } - readIORef ref
+ let copied= bytes `min` (w - r)
+ remaining = bytes - copied
+ newr = r + copied
+ newbuf | newr == w = buf{ bufRPtr = 0, bufWPtr = 0 }
+ | otherwise = buf{ bufRPtr = newr }
+ --memcpy_ba_baoff marr# raw (fromIntegral r) (fromIntegral copied)
+ memcpy_ba_baoff marr# raw (fromIntegral r) (fromIntegral copied)
+ writeIORef ref newbuf
+ readChunkBU fd is_stream marr# copied remaining
+ stToIO (unsafeFreezeAllMBU marr)
+
hunk ./Data/Array/Vector/UArr.hs 59
- BUArr, MBUArr, UAE,
- lengthBU, indexBU, sliceBU, hGetBU, hPutBU,
+ BUArr, MBUArr, UAE(..),
+ lengthBU, indexBU, sliceBU, hGetBU, hGetLengthBU, hPutBU,
hunk ./Data/Array/Vector/UArr.hs 867
+ hGetLengthU :: Int - Handle - IO (UArr a)
hunk ./Data/Array/Vector/UArr.hs 875
+primGetLengthU :: UPrim a = Int - Handle - IO (UArr a)
+primGetLengthU n = liftM mkUAPrim . hGetLengthBU n
+
hunk ./Data/Array/Vector/UArr.hs 880
-instance UIO Bool where hPutU = primPutU; hGetU = primGetU
-instance UIO Char where hPutU = primPutU; hGetU = primGetU
-instance UIO Intwhere hPutU = primPutU; hGetU = primGetU
-instance UIO Word where hPutU = primPutU; hGetU = primGetU
-instance UIO Float where hPutU = primPutU; hGetU = primGetU
-instance UIO Double where hPutU = primPutU; hGetU = primGetU
+instance UIO Bool where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Char where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Intwhere hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Word where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Float where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Double where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
hunk ./Data/Array/Vector/UArr.hs 887
-instance UIO Word8 where hPutU = primPutU; hGetU = primGetU
-instance UIO Word16 where hPutU = primPutU; hGetU = primGetU
-instance UIO Word32 where hPutU = primPutU; hGetU = primGetU
-instance UIO Word64 where hPutU = primPutU; hGetU = primGetU
+instance UIO Word8 where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Word16 where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Word32 where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
+instance UIO Word64 where hPutU = primPutU; hGetU = primGetU; hGetLengthU =
primGetLengthU
hunk ./Data/Array/Vector/UArr.hs 892
-instance UIO Int8 where hPutU = primPutU; hGetU = primGetU
-instance UIO Int16 where hPutU = primPutU; hGetU = primGetU
-instance UIO Int32 where hPutU = primPutU; hGetU = primGetU
-instance UIO Int64 where hPutU = primPutU; hGetU = primGetU
+instance UIO Int8 where hPutU = primPutU; hGetU = primGetU;
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
manlio_perillo: Don Stewart ha scritto: [...] So, the patch is: just revert this change. Or... use your own UIO instance. That's why it's a type class! Why should I rewrite the UIO instance, if one already exists? Oh, because you want different serialization semantics to the (arbitrary) defaults. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] broken IO support in uvector package, when using non primitive types
The main issue seems to be that although the semantics of UIO may be arbitrary, Wallace's patch actually broke deserialization for any production-based UArr, and I'm not sure the benefits are worthwhile (loading a file someone else sent you) given that endianness is already not taken into account when loading (so the chances of someone giving you a raw binary file that happens to contain values of the correct endianness is rather low, it seems). On a related note, having a (more) complete testsuite might help prevent patches like this from breaking existing functionality. Maybe a way to resolve the issue is to use the file size and break it according to the size of the two halves of the production? This avoids prefixing array length, but allows the productions to still work. Either way, I'm in the process of writing a Binary instance, so maybe we can get the best of both worlds eventually. Thanks, Dan On Fri, Mar 13, 2009 at 7:21 PM, Don Stewart d...@galois.com wrote: manlio_perillo: Don Stewart ha scritto: [...] So, the patch is: just revert this change. Or... use your own UIO instance. That's why it's a type class! Why should I rewrite the UIO instance, if one already exists? Oh, because you want different serialization semantics to the (arbitrary) defaults. -- Don ___ 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] broken IO support in uvector package, when using non primitive types
I'd like to do away with UIO altogether though. pumpkingod: The main issue seems to be that although the semantics of UIO may be arbitrary, Wallace's patch actually broke deserialization for any production-based UArr, and I'm not sure the benefits are worthwhile (loading a file someone else sent you) given that endianness is already not taken into account when loading (so the chances of someone giving you a raw binary file that happens to contain values of the correct endianness is rather low, it seems). On a related note, having a (more) complete testsuite might help prevent patches like this from breaking existing functionality. Maybe a way to resolve the issue is to use the file size and break it according to the size of the two halves of the production? This avoids prefixing array length, but allows the productions to still work. Either way, I'm in the process of writing a Binary instance, so maybe we can get the best of both worlds eventually. Thanks, Dan On Fri, Mar 13, 2009 at 7:21 PM, Don Stewart d...@galois.com wrote: manlio_perillo: Don Stewart ha scritto: [...] So, the patch is: just revert this change. Or... use your own UIO instance. That's why it's a type class! Why should I rewrite the UIO instance, if one already exists? Oh, because you want different serialization semantics to the (arbitrary) defaults. -- Don ___ 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] reddit.com/r/haskell_proposals: Relevance to Google Summer of Code?
NOTE: This message was originally posted to the subreddit in question (and has been slightly modified), where I was told that I should post the question on haskell-cafe. See http://www.reddit.com/r/haskell_proposals/comments/847by/ask_relevance_to_google_summer_of_code/ I'm currently researching the possibility of applying for the Google Summer of Code[1] and (by way of dons's post[2]) have found myself perusing the Haskell Proposals subreddit for project ideas. As an accepted MS CS student, I've spent my undergraduate life annoying professors by using a slew of different programming languages -- most recently, Haskell. While not altogether unfamiliar with the language, I rather doubt (or at least try to honestly question) how useful a contributor I'd be to some of the larger projects that have been posted (e.g., the Immix garbage collector[3] or loop unrolling[4]), despite some of their acceptances as tickets on the Summer of Code Trac[5] and my deep interest in compiler language theory. There are projects that match other interests of mine and (in my approximation) my experience level, but they also tend to be smaller. For example, the reddit-alike[6] or wiki-embedded Haddock[7]. So, background sap-story notwithstanding, I suppose my general question is: with respect to the aforementioned Summer of Code post, is this subreddit meant to be a place for appropriate SoC projects? It doesn't feel quite like it is, but I would be excited to work on some of those that I indicated. The telltale sign for a project's worthiness seems to be that a ticket is already opened on the Trac that spells out the appropriateness, but this is limiting. More obviously, to test the fitness of a project, should the idea be opened as a ticket for the cursory review of others? Should someone who wants to do Summer of Code work be at any particular level of experience (dive into GHC's backend versus use Haskell to hack on a project)? Intuitively, 1 summer's worth of work could probably be found in any corner of code that meshes with any student's expertise and interests -- even a reddit-alike can actually be a lot of work. But the catch (for me) is that when familiarity is relatively low, it's hard to come up with such ideas. I realize that applications are competitive against other students, so the range of acceptable submissions would depend more on the other applicants, but I think it's also important to address haskell.org's ethos with regards to who they're looking for. If there's a more appropriate place to post this question (ha! singular) I'm more than happy to transplant it. [1] http://code.google.com/soc/ [2] http://www.reddit.com/r/programming/comments/7zfog/anybody_done_the_google_summer_of_code_your/c07twkd [3] http://www.reddit.com/r/haskell_proposals/comments/7wjsc/implement_the_immix_garbage_collector_in_ghc/ [4] http://www.reddit.com/r/haskell_proposals/comments/7z1uf/implement_loop_unrolling_for_c_level_loops_in_ghc/ [5] http://hackage.haskell.org/trac/summer-of-code/wiki/Soc2009 [6] http://www.reddit.com/r/haskell_proposals/comments/7u48x/a_simple_redditlike_happsbased_proposal_voting/ [7] http://www.reddit.com/r/haskell_proposals/comments/7qnwq/haddock_with_embedded_wiki_feature_a_la_rwh_so_we/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell-Wiki Account registration
On Fri, 13 Mar 2009, Benjamin L.Russell wrote: Why not ask new users to identify letters in a random bitmapped image of a string, as is commonly done? I assume, because those images are 1) not accessible by blind people 2) can be decoded by spammers, since they know how the images are generated by common software. Thus my suggestion was a simple Haskell specific question, which cannot be answered by stupid spambots. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] bytestring vs. uvector
On Mon, 9 Mar 2009, Alexander Dunlap wrote: - uvector, storablevector and vector are all designed for dealing with arrays. They *can* be used for characters/word8s but are not specialized for that purpose, do not deal with Unicode at all, and are probably worse at it. They are better for dealing with things that you would generally use arrays for. Since the Storable instance of Char stores 32 bit values, I expect they store full Unicode codes and thus StorableVector can be used for Unicode strings without loss. They will require more memory than UTF8 strings, but whether they are faster or slower will depend on how expensive UTF8 decoding/encoding is. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Incompatibility of different (monad transformer) libraries
On Tue, 10 Mar 2009, ariep wrote:
Problem instance
In my code, I use some monad transformers. I used to use the mtl package,
but I recently switched to the combination transformers/monads-tf
(mainly for the Applicative instances).
The same code also uses the haskeline library, for line reading.
Haskeline allows to edit the user's history (previously entered lines), but
only through a Control.Monad.State interface, and that happens to be the
Control.Monad.State from mtl. So now, my package also needs to import
mtl.
This combination of package dependencies gives import conflicts: whenever I
import some Control.Monad.{State,Error,Cont,...} module, there is more than
one package providing such a module.
I think 'transformers' exports Control.Monad.Trans.State. This should not
conflict with MTL. However, MTL's State type is different from
transformer's one. Is that your problem?
Solution?
For now, I resolve the ambiguity by using Package imports, i.e. annotate
the ambiguous imports by the right package name.
Is this the best solution? The ghc manual states, that the package import
extension should not be necessary. I can think of another solution, by
creating a dedicated package, which imports mtl:Control.Monad.* and
re-exports them under another name, but that's even less elegant than
package imports.
Since the 'cabal' tool became better and better, today I use a cabal file
even for small programs. Cabal automatically calls GHC with the right
package exposing and hiding options.
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Style Guide for Haskell Code
On Tue, 10 Mar 2009, Manlio Perillo wrote: After a quick search with Google, it seems that there is not yet an official document for Style Guide for Haskell Code. I was only able to found: http://www.cs.caltech.edu/courses/cs11/material/haskell/misc/haskell_style_guide.html http://urchin.earth.li/~ian/style/haskell.html http://github.com/tibbe/haskell-style-guide/tree/master and, of course, the GHC style guide. Ah, why does Google not show http://haskell.org/haskellwiki/Category:Style ? Of course, style is a matter of taste. So there are as many good styles as programmers and there won't be an official style guide, I'm afraid. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Microsoft PhD Scholarship at Strathclyde
On Tue, 10 Mar 2009, Conor McBride wrote:
Apologies for crossposting. Please forward this message
to individuals or lists who may be interested. In addition
to the recently advertised PhD position at Strathclyde on
Reusability and Dependent Types, I am delighted to
advertise the following PhD opportunity.
{-
-- Haskell Types with Numeric Constraints
-}
Sounds like it could simplify
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dimensional/
a lot. However, isn't this halfheartedly since we all wait for full
dependent types? :-)
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A systematic method for deriving a defintion of foldl using foldr?
On Wed, 11 Mar 2009, R J wrote: foldl and foldr are defined as follows: foldr :: (a - b - b) - b - [a] - b foldr f e [] = e foldr f e (x : xs) = f x (foldr f e xs) foldl :: (b - a - b) - b - [a] - b foldl f e [] = e foldl f e (x : xs) = foldl f (f e x) xs 1. I understand how these definitions work, and yet I'm unable to implement foldl in terms of foldr. What's a systematic approach to identifying such an implementation, and what is the implementation? You are lucky, I recently wrote http://haskell.org/haskellwiki/Foldl_as_foldr___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] State monad is missing Applicative instance
On Thu, 12 Mar 2009, Peter Verswyvelen wrote: I think. Or is it defined in some other package? The 'transformers' package has those instances. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Abuse of the monad [was: monadic logo]
On Thu, 12 Mar 2009, Andrew Wagner wrote: Can you expand on this a bit? I'm curious why you think this. http://haskell.org/haskellwiki/Type_classes_are_for_reusability We recently had a thread about that. I can't find it now. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
