Re: [Haskell-cafe] Re: Allowing hyphens in identifiers
x - take_while some_condition some_list and x - takeWhile someCondition someList x - take-while some-condition some-list As someone who is dyslexic, I find both camelCase and dashes far easier to read than underscores. I find it hard to count the words in the underscore version - the underscores and spaces confuse me. Dashes do not, presumably because they are 'within' the line of sight for the letters. However, I can't help feeling that if we use good IDEs, we could 'internationalize' identifiers into english/french/chinese/camel/dash or whatever. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Implicit newtype unwrapping
Perhaps what you are looking for is a more powerful defining semantics? newtype MyFoo = Foo defining (Foo(..)) -- all class instances that Foo has are delegated through from MyFoo Matthew not sure if this is what you are thinking at, but everytime I wrap a type Foo in a newtype MyFoo to define my own instances (or just for more expressiveness code), I wish I had a way to tell the compiler: „Please define function myfoo to be the same as foo, with all occurences of Foo in its type signature replaced by MyFoo.“ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Implicit newtype unwrapping
Of course, I meand 'deriving', not 'defining' /me embarsed 2009/12/3 Matthew Pocock matthew.poc...@ncl.ac.uk Perhaps what you are looking for is a more powerful defining semantics? newtype MyFoo = Foo defining (Foo(..)) -- all class instances that Foo has are delegated through from MyFoo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Graph drawing library for Haskell
I have had some luck with the graphviz (dotter) bindings for drawing node/ark graphs. It's not an ideal solution, and will require some wrappers to bind to your data structures, but it does work. Matthew 2009/11/20 Victor Mateus Oliveira rhapso...@gmail.com Hi, Anyone knows a good library for graph diagram drawing? Or a haskell binding for one? Something like jgraph. http://www.jgraph.com/jgraph.html []s' Victor -- GNU/Linux user #446397 - http://counter.li.org ___ 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] Re: Long running Haskell program
2009/11/12 Heinrich Apfelmus apfel...@quantentunnel.de Interestingly, this is different from Control.Monad.State.Strict . The latter never forces the state itself, just the pair constructor of the (result,state) pair. Yes. This bit me the first time I came across it. I think we need a Control. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Long running Haskell program
2009/11/12 Heinrich Apfelmus apfel...@quantentunnel.de Interestingly, this is different from Control.Monad.State.Strict . The latter never forces the state itself, just the pair constructor of the (result,state) pair. Yes. This bit me the first time I came across it. I think we need a Control.Monad.State.StrictOnState with strict behaviour on the state value. I notice this same underlying issue is coming up in more than one thread on these lists. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Long running Haskell program
How about: instance (Monad m) = MonadState s (SStateT s m) where get = S get put s = S (put $ using s $ strategy m) where our state monad has a strategy field? Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Long running Haskell program
Is there a state monad that is strict on the state but lazy on the computation? Of course, strictness in the state will force a portion of the computation to be run, but there may be significant portions of it which are not run. Would there be a way to write a state monad such that it is entirely lazy, but then to wrap either the computation or the state in an 'eager' strategy datatype which takes care of this in a more flexible manner? Thanks, Matthew 2009/11/11 Bryan O'Sullivan b...@serpentine.com On Wed, Nov 11, 2009 at 7:43 AM, David Leimbach leim...@gmail.com wrote: I recently ran into some serious space leak difficulties that would ultimately cause this program to crash some time after startup (my simulator is also written in Haskell, and runs a LOT faster than the real application ever could, this has enabled me to fast forward a bit the data growth issues and crash in minutes instead of days!) It sounds to me like you were storing a Map in a StateT. Since the usual State and StateT monads don't force the evaluation of their payload, I'm not terribly surprised that such a leak should arise. ___ 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] Re: Libraries need a new owner
On Monday 24 March 2008, Don Stewart wrote: Let's get a new faster Data.Map and other containers ready to go by the end of the northern summer? And while we are visiting this, can I put in a vote for a seperation between the default Data.* container concrete implementations and associated classes? E.g. between the cannonical Map implementation and a Map class that could (if I felt mad) be backed by a list, or (if I was more sane) the cannonical Map datatype? This would go /at least/ for Map, Set, List. Matthew -- 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] Random Monad
Hi, Who currently maintains the Random monad code? I have some patches to contribute. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Random Monad
On Monday 24 March 2008, Henning Thielemann wrote: On Mon, 24 Mar 2008, Matthew Pocock wrote: Who currently maintains the Random monad code? I have some patches to contribute. Do you refer to the code on the wiki? No, to the code in darcs at http://code.haskell.org/monadrandom Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hoisting as well as lifting and returning
Hi, Happy Easter! I've been using monad transformers for the first time in anger this week. They certainly do the job. However, there's an operation that I keep defining over and over again. It is sort of like lift and return in that it's glue to get operations and values into the monad from outside it. Here are two examples. hoistList :: (Monad m) = [a] - ListT m a hoistList = foldr (mplus . return) mzero hoistMaybe :: (Monad m) = Maybe a - MaybeT m a hoistMaybe = maybe mzero return The general idea is that you have some legacy, non-transform operation in some monad MonadFoo, and you are writing an operation in MonadFooT. You want to get the monadFoo value into MonadFooT. So, you say something like: do vInMFT - hoist vInMF Is this a common enough operation on a monad transformer and it's 'raw' monad to warrant a class of its own? I have 'hoist' methods for several monad transformers, including RamdomMonadT, although I've probably defined them in ways that are overly eager or eat stack/heap, so I'd prefer knowledgable people to write them :) There must be other operations that link the base monad with its transformed version, other than 'hoist' - the runFooT method for example. Perhaps 'hoist' already exists and I'm re-inventing the wheel? Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hoisting as well as lifting and returning
Hi Yitz, I was thinking along the lines of a class linking the monad transformer with the base monad: class (MonadTrans mt, Monad b) = MonadTForm mt b | mt - b where hoist :: (Monad m) = b a - mt m a This is to restrict it directly between the base monad and the transformed version. If you wish to 'adapt' any other pair of monads, then I think that's another operation, just as lift is a different operation to hoist. Matthew On Sunday 23 March 2008, Yitzchak Gale wrote: You are correct. This is a fundamental operation. It exists for just about every monad, but in a haphazard and inconsistent way. In my opinion, its type needs to be more polymorphic in a slightly different direction than what you are suggesting. ... What I do sorely feel the need for is a hoist for each pair of base/transformer monads: i.e., polymorphic monad constructors. So, for example, if we had mkState :: (st - (a, st)) - m a as a member of the MonadState st m class, then it would be so much easier to write functions f :: MonadState st m = ... that could be used without having to refactor it every time the monad stack changes. In general, each monad Foo would have a MonadFoo class (even the monads that don't have one yet) containing (at least) a mkFoo method that lifts the underlying structure polymorphically either to Foo or to FooT. ... Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] classes for data structures
Hi, I've been working a lot with maps, sets and lists. While the process of getting things out of them is abstracted by foldable, traversable and friends, the process of building one up is not. Would it be possible to have something like: class Buildable b where empty :: b a --makes an empty b with elements of type a insert :: a - b a - b a --inserts the new element into the buildable I'm not particularly wedded to the names. It's just that it would be very convenient sometimes to collect data items into e.g. a list or a set, without pushing in some klunky foralled insert function. I see that this is realted to MonadPlus, but the space of possible container classes is wider than that of monads e.g. set. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Signature for non-empty filter
On Wednesday 06 February 2008, Henning Thielemann wrote: If the type checker does not terminate because the checked function does not terminate on the example input, then the function does not pass the type check and as a compromise this would be ok. Can't fault this logic. The problem is that you may have to wait quite a long time to discover this non-termination. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell maximum stack depth
On Monday 04 February 2008, Adrian Hey wrote: Yikes! Also, I can't help thinking that the common justification for the current limit (that it helps find alleged bugs) is a little lame. It only helps find bugs if one expects ones program to use less than 8M of stack (hence if it's using more, it's a bug by ones *own* definition). My experience so far is that I've only triggered stack overflows when I've had an infinite recursion. Getting foldl and foldr wrong on long lists has usually lead to disasterous memory churn, not ever to an overflow. Regards -- Adrian Hey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell maximum stack depth
On Monday 04 February 2008, Neil Mitchell wrote: Hi That would be nice. But its only beneficial if there are programs which takes large amounts of stack at some point, but then shrink down to very little stack and continue for a reasonable amount of time. From the 'when I was a lad' department... Thinking back to when Java transitioned to a garbage collector that could give memory back to the OS, we got some unexpected benefits. Consider a machine that's running a load of programs, launched from some q system e.g. LSF/condor. If they keep memory, the box, q scheduler or admins get unhappy. If I had £1 for each time our admins said your 200 java apps are using 500m each when I could see for sure that except for an initial memory burn during loading files in, only a few megs where resident. Magically, once Java could release heap, these grypes went away. Matthew Thanks Neil ___ 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] Re: Re: hxt memory useage
On Monday 28 January 2008, Rene de Visser wrote: It would be nice if HXT was incremental even when you are processing the whole tree. If I remember correctly, the data type of the tree in HXT is something like data Tree = Tree NodeData [Tree] which means that already processed parts of the tree can't be garbage collected because the parent node is holding onto them. If instead it was data Tree = Tree NodeData (IORef [Tree]) Would could remove each subtree as it was processed (well just before would probably be necessary, and we would need to rely on blackholing to remove the reference on the stack). This would perhaps allow already processed subtree to be garbage collected. Together with the lazy evaluation this could lead to quite good memory usage. Rene. Not so sure about this. For streaming processing, it would be nicer to have something like StAX with a stack of already entered elements kept about as book-keeping |(the tags + attribute sets to root). Let's face it, if you sign up to a document model, you are signing up to a document and shouldn't be supprised when it sits in memory. I think the 'right' solution at least in part goes with the problem to be solved. I'd be upset if we moved to something more complex where my code breaks because something accidentaly garbage collected data that I need to back-track to. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hxt memory useage
On Saturday 26 January 2008, Keith Fahlgren wrote: Perhaps a more modern approach would be StAX[1]-like rather than SAX-like? In either case, streaming, non-DOM. I am concerned by the number of people expressing willingness to abandon namespace support, but perhaps I'm being too much of a purist Keith StAX is fine for a very wide range of applications, including web services. In the web-service domain, namespaces and entity expansion and xsd are not optional extras, but these can be layered on top of StAX rather than a more DOM-like structure. Just as a reality check, we regularly stream xml messages between web services in Java where the message bodies are many gig in size, using StAX, and neither the client or server need anything other than a constant memory overhead, as the portions of the message are generated and consumed in a streaming manner. It would be very nice if we could do similar things in haskell. Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] hxt memory useage
Hi, I've been using hxt to process xml files. Now that my files are getting a bit bigger (30m) I'm finding that hxt uses inordinate amounts of memory. I have 8g on my box, and it's running out. As far as I can tell, this memory is getting used up while parsing the text, rather than in any down-stream processing by xpickle. Is this a known issue? Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hxt memory useage
On Thursday 24 January 2008, Albert Y. C. Lai wrote: Matthew Pocock wrote: I've been using hxt to process xml files. Now that my files are getting a bit bigger (30m) I'm finding that hxt uses inordinate amounts of memory. I have 8g on my box, and it's running out. As far as I can tell, this memory is getting used up while parsing the text, rather than in any down-stream processing by xpickle. Is this a known issue? Yes, hxt calls parsec, which is not incremental. haxml offers the choice of non-incremental parsers and incremental parsers. The incremental parsers offer finer control (and therefore also require finer control). I've got a load of code using xpickle, which taken together are quite an investment in hxt. Moving to haxml may not be very practical, as I'll have to find some eqivalent of xpickle for haxml and port thousands of lines of code over. Is there likely to be a low-cost solution to convincing hxt to be incremental that would get me out of this mess? Matthew ___ 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] parsec and bytestring; was: hxt memory useage
Would a bytestring-backed implementation of parsec solve my problems? Is there such a beast out there? Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using GADTs
On Sunday 29 July 2007, Jim Apple wrote: The way I would do this would be to encode as much of the value as I cared to in the constructors for concepts, rather than just encoding the top-level constructor. data Named data Equal a b data Negation a data Top data Concept t where CNamed :: String - Concept Named CEqual :: Concept a - Concept b - Concept (Equal a b) CNegation:: Concept a - Concept (Negation a) CTop :: Concept Top Ah, great. That was the first trick I'd missed. Then, I could form a datatype that does not contain a Concept, but merely certifies that all Concepts of a certain type are in NNF. This turns out not to be needed if you describe what nnf is in terms of those parameterised datatypes above. You can re-use the same datatype! I had to move the nnf function into a class to get it to compile, which makes the code more verbose, but appart from that I'm quite pleased with the result. By the way, the code you included last time did not compile. I think you'll probably get a quicker response than my lazy two-day turnaround if you make sure to run your posted code through Your Favorite Compiler first. Yeah, sorry about that. It was a late-at-night thing. I've pasted in my (compiling and working) code below, for anyone that's interested. I think I like GADTs quite a lot :) Pitty I can't get deriving clauses to work with them... Thanks Matthew data Named data Equal a b data Conjunction a b data Disjunction a b data Negation a data Existential a data Universal a data Top data Bottom data Concept t where CNamed :: String - Concept Named CEqual :: Concept a - Concept b - Concept (Equal a b) CConjunction :: Concept a - Concept b - Concept (Conjunction a b) CDisjunction :: Concept a - Concept b - Concept (Disjunction a b) CNegation:: Concept a - Concept (Negation a) CExistential :: Role Named - Concept a - Concept (Existential a) CUniversal :: Role Named - Concept a - Concept (Universal a) CTop :: Concept Top CBottom :: Concept Bottom data Role t where RNamed :: String - Role Named class InNNF nnf instance InNNF Named instance InNNF Top instance InNNF Bottom instance InNNF (Negation Named) instance InNNF (Negation Top) instance InNNF (Negation Bottom) instance (InNNF a, InNNF b) = InNNF (Equal a b) instance (InNNF a, InNNF b) = InNNF (Conjunction a b) instance (InNNF a, InNNF b) = InNNF (Disjunction a b) instance (InNNF a) = InNNF (Existential a) instance (InNNF a) = InNNF (Universal a) class ( InNNF u ) = ToNNF t u | t - u where nnf :: Concept t - Concept u instance ToNNF Named Named where nnf = id instance (ToNNF a c, ToNNF b d) = ToNNF (Equal a b) (Equal c d) where nnf (CEqual lhs rhs) = CEqual (nnf lhs) (nnf rhs) instance (ToNNF a c, ToNNF b d) = ToNNF (Conjunction a b) (Conjunction c d) where nnf (CConjunction lhs rhs) = CConjunction (nnf lhs) (nnf rhs) instance (ToNNF a c, ToNNF b d) = ToNNF (Disjunction a b) (Disjunction c d) where nnf (CDisjunction lhs rhs) = CDisjunction (nnf lhs) (nnf rhs) instance (ToNNF a b) = ToNNF (Existential a) (Existential b) where nnf (CExistential r c) = CExistential r (nnf c) instance (ToNNF a b) = ToNNF (Universal a) (Universal b) where nnf (CUniversal r c) = CUniversal r (nnf c) instance ToNNF (Negation Named) (Negation Named) where nnf = id instance (ToNNF (Negation a) c, ToNNF (Negation b) d) = ToNNF (Negation (Equal a b)) (Equal c d) where nnf (CNegation (CEqual lhs rhs)) = CEqual (nnf $ CNegation lhs) (nnf $ CNegation rhs) instance (ToNNF (Negation a) c, ToNNF (Negation b) d) = ToNNF (Negation (Conjunction a b)) (Disjunction c d) where nnf (CNegation (CConjunction lhs rhs)) = CDisjunction (nnf $ CNegation lhs) (nnf $ CNegation rhs) instance (ToNNF (Negation a) c, ToNNF (Negation b) d) = ToNNF (Negation (Disjunction a b)) (Conjunction c d) where nnf (CNegation (CDisjunction lhs rhs)) = CConjunction (nnf $ CNegation lhs) (nnf $ CNegation rhs) instance (ToNNF a b) = ToNNF (Negation (Negation a)) b where nnf (CNegation (CNegation c)) = nnf c instance(ToNNF (Negation a) b) = ToNNF (Negation (Existential a)) (Universal b) where nnf (CNegation (CExistential r c)) = CUniversal r (nnf $ CNegation c) instance (ToNNF (Negation a) b) = ToNNF (Negation (Universal a)) (Existential b) where nnf (CNegation (CUniversal r c)) = CExistential r (nnf $ CNegation c) instance ToNNF (Negation Top) (Negation Top) where nnf (CNegation CTop) = CNegation CTop instance ToNNF (Negation Bottom) (Negation Bottom) where nnf (CNegation CBottom) = CNegation CBottom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Using GADTs
Hi, I'm trying to get to grips with GADTs, and my first attempt was to convert a simple logic language into negative normal form, while attempting to push the knowledge about what consitutes negative normal form into the types. My code is below. I'm not entirely happy with it, and would appreciate any feedback. The rules are that in nnf, only named concepts, the concept Top and the concept Bottom can be negated. So, I've added three NNFNegation_* constructors capturing these legal cases. Is there a way to use one constructor, that is allowed to 'range over' these three cases and none of the others? I've ended up producing two data types, one for the general form and one for the nnf. Actually, the constraint on what constitutes nnf is fairly obvious - no complex terms are negated. Is there a way to use just the one data type but to describe two levels of constraints - one for the general case, and one for the nnf case? Or is the whole point that you capture each set of constraints in a different data type? Thanks, Matthe data Named data Equal data Conjunction data Disjunction data Negation data Existential data Universal data Top data Bottom data Concept t where CNamed :: String - Concept Named CEqual :: Concept a - Concept b - Concept Equal CConjunction :: Concept a - Concept b - Concept Conjunction CDisjunction :: Concept a - Concept b - Concept Disjunction CNegation:: Concept a - Concept Negation CExistential :: Role Named - Concept Existential CUniversal :: Role Named - Concept Universal CTop :: Concept Top CBottom :: Concept Bottom data NNFConcept t where NNFCNamed :: String - NNFConcept Named NNFCEqual :: NNFConcept a - NNFConcept b - NNFConcept Equal NNFCConjunction :: NNFConcept a - NNFConcept b - NNFConcept Conjunction NNFCDisjunction :: NNFConcept a - NNFConcept b - NNFConcept Disjunction NNFCExistential :: Role Named - NNFConcept Existential NNFCUniversal :: Role Named - NNFConcept Universal NNFCTop :: NNFConcept Top NNFCBottom :: NNFConcept Bottom NNFCNegation_N :: NNFConcept Named - Concept Negation NNFCNegation_T :: NNFConcept Top- Concept Negation NNFCNegation_B :: NNFConcept Bottom - Concept Negation data Role t where RNamed :: String - RNamed Named -- terms not prefixed with a negation are already in nnf nnf :: Concept t - NNFConcept u nnf CNamed name = NNFCNamed name nnf CEqual lhs rhs = NNFConcept (nnf lhs) (nnf rhs) nnf CConjunction lhs rhs = NNFCConjunction (nnf lhs) (nnf rhs) nnf CDijunction lhs rhs = NNFCDisjunction (nnf lhs) (nnf rhs) nnf CExistential rc = NNFCExistential r (nnf c) nnf CUniversal rc = NNFCUniversal r (nnf c) -- if negated, we must look at the term and then do The Right Thing(tm) nnf CNegation (CNamed name) = NNFCNegation_N NNFCNamed name nnf CNegation (CEqual lhs rhs) = NNFCEqual (nnf $ CNegation lhs) (nnf $ CNegation rhs) nnf CNegation (CConjunction lhs rhs) = NNFCDisjunction (nnf $ CNegation lhs) (nnf $ CNegation rhs) nnf CNegation (CDisjunction lhs rhs) = NNFCConjunction (nnf $ CNegation lhs) (nnf $ CNegation rhs) nnf CNegation (CNegation c) = nnf c nnf CNegation (CExistential r c) = NNFCUniversal r (nnf $ CNegation c) nnf CNegation (CUniveralr c) = NNFCExistential r (nnf $ CNegation c) nnf CNegation CTop = NNFCNegation_T NNFCTop nnf CNegation CBottom= NNFCNegation_B NNFCBottom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] partial kinds and instances
Hi, I saw that it's possible to peal off kinds from the right-hand side when instantiating classes. Is it possible to peel them off from the left-hand side? Or in any order? I have been told in #haskell by people who seems to know that Very Bad Things happen if you do this without also making the kind system more clever. Is there a quick fix that will give me the same effect, without introducing a newtype or re-writing the original type declaration to introduce the extra types in a different order? Illustrative code below. Matthew data MyType e = Singleton e data MyOtherType k v = Empty | Node k v data YetAnotherType k v = OtherEmpty | OtherNode k v type RevYAT v k = YetAnotherType k v class Iterable ite where iterate :: ite e - [e] instance Iterable MyType where iterate (Singleton e) = [e] instance Iterable (MyOtherType k) where iterate ite = [] --broken but illustrative instance Iterable (RevYAT v) where iterate it = [] --broken again Type synonym `RevMOM' should have 2 arguments, but has been given 1 In the instance declaration for `Iterable (RevYAT v)' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell - fpga
Hi, Does anybody know of any compilers that can compile portions of a haskell program to an FPGA? I have found a few domain-specific languages implemented in haskell for FPGAs, but so far no back-ends for compilers like ghc. Thanks, Matthew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
