Re: [Haskell-cafe] Fwd: [Haskell-beginners] Monad instances and type synonyms

The point in not allowing partially applied type synonym instances is that it'd make deciding whether a type is an instance of a class much harder. Cf. here[1] for a similar question with the Category class. -- Steffen [1] Attached message. Couldn't find it on the archives.. On 04/14/2013 0

Re: [Haskell-cafe] code-as-config, run-time checks and error locations

This one[1] sounds so awesome! I just read the paper. In particular I like how one could access the current call stack structure live. However, the most recent changes to the code are from early 2009. Anyone knows what happened to this? [1] http://hackage.haskell.org/trac/ghc/wiki/ExplicitCa

Re: [Haskell-cafe] code-as-config, run-time checks and error locations

Sun, Apr 7, 2013 at 12:23 AM, Steffen Schuldenzucker wrote: For the moment I think it would be enough to auto-insert the location of calls to a certain set of functions. Have you tried assert [1]? [1] http://hackage.haskell.org/packages/archive/base/4.6.0.1/doc/html/Control-Exception.html#v:asse

[Haskell-cafe] code-as-config, run-time checks and error locations

Dear Café, I'm working on a EDSL that will include both type checks (at compile time) and semantic checks (at run time). - Semantic properties are known at compile time but feel too complex to me to be encoded in the type system. If one of the runtime checks fails, I'd like to print the location

Re: [Haskell-cafe] monoid pair of monoids?

Hi Christopher, On 12/21/2012 09:27 AM, Christopher Howard wrote: [...] Of course, I thought it would be likely I would want other classes and instances with additional numbers of types: code: data Socket3 a b c = Socket3 a b c deriving (Show) instance (Monoid a, Monoid b, Monoid

[Haskell-cafe] ANNOUNCE: apphointments - A simple functional calendar

Using just haskell instead of our own language or GUI allows great flexibility in both defining events and generating reports. See e.g. the 'lecture' combinator from Apphointments.Util. Status -- Works for me, but has no features yet. See TODO. Credi

Re: [Haskell-cafe] How to define a Monad instance

On 07/28/2012 03:35 PM, Thiago Negri wrote: > [...] As Monads are used for sequencing, first thing I did was to define the following data type: data TableDefinition a = Match a a (TableDefinition a) | Restart So TableDefinition a is like [(a, a)]. [...] > So, to create a replacement table:

Re: [Haskell-cafe] Finding the average in constant space

Hi Chris, On 05/27/2012 10:04 AM, Chris Wong wrote: I just came up with a way of executing multiple folds in a single pass. In short, we can write code like this: average = foldLeft $ (/)<$> sumF<*> lengthF and it will only traverse the input list once. The code is at: https://gist.git

Re: [Haskell-cafe] [Haskell] ANNOUNCE: notcpp-0.0.1

On 04/13/2012 10:49 PM, Ben Millwood wrote: I'm pleased to announce my first genuinely original Hackage package: notcpp-0.0.1! http://hackage.haskell.org/package/notcpp [...] Why is it > scopeLookup :: String -> Q Exp with n bound to x :: T => @scopeLookup n@ evaluates to an Exp containing

Re: [Haskell-cafe] Understanding GC time

On 03/10/2012 07:50 PM, Thiago Negri wrote: I see. Thanks for the answers. Any data structure or source annotation that would prevent that? For example, if I try the same program to run on a [1..] list, I'll get an out of memory error for the single-threaded version. Any way t

Re: [Haskell-cafe] STM atomic blocks in IO functions

On 01/14/2012 03:55 PM, Ketil Malde wrote: "Bryan O'Sullivan" writes: The question is a simple one. Must all operations on a TVar happen within *the same* atomically block, or am I am I guaranteed thread safety if, say, I have a number of atomically blocks in an IO function. If you want suc

Re: [Haskell-cafe] named pipe interface

On 01/12/2012 07:53 PM, Serge D. Mechveliani wrote: [...] > For the "to-A" part writen in C (instead of Haskell), this interface loop works all right. With Haskell, I manage to process only a single string in the loop, and then it ends with an error. Main.hs is given below. I never dealt w

Re: [Haskell-cafe] Simple type-class experiment turns out not so simple...

On 01/06/2012 11:51 AM, Steve Horne wrote: On 06/01/2012 10:29, Steffen Schuldenzucker wrote: On 01/06/2012 11:16 AM, Steve Horne wrote: >>> [...] module BinTree ( WalkableBinTree, BT (Branch, Empty) ) where -- n : node type -- d : data item type wrapped in each node class Walkab

Re: [Haskell-cafe] Simple type-class experiment turns out not so simple...

On 01/06/2012 11:16 AM, Steve Horne wrote: I was messing around with type-classes (familiarization exercises) when I hit a probably newbie problem. Reducing it to the simplest case... module BinTree ( WalkableBinTree, BT (Branch, Empty) ) where -- n : node type -- d : data item type wrapped i

Re: [Haskell-cafe] Anonymous, Unique Types, maybe

Hi Scott, a good idea. Why not use an existential to encode your types like myMap :: (a -> b) -> a-list of length n -> b-list of length n myFilter :: (a -> Bool) -> a-list of length n -> exists m. a-list of length m , where the first case is modeled using a type annotation and the seco

Re: [Haskell-cafe] Anonymous, Unique Types, maybe

On 12/04/2011 06:53 AM, Scott Lawrence wrote: [...] Some operators might take more than one list/stream as an argument, combining them in some way or another. Obviously, if the lists were different lengths, the operator would fail. I don't want that to happen at run time, so I want to check for

Re: [Haskell-cafe] Fwd: Is it possible to represent such polymorphism?

On 10/05/2011 11:30 PM, Alberto G. Corona wrote: if Hlist is sugarized as variable length tuples, then the initial code would compile without noticing the use of HList... Seems to me like the advantage of such a sugaring would be that people could use a complex framework without actually havi

Re: [Haskell-cafe] Problem on using class as type.

On 10/03/2011 10:42 PM, Magicloud Magiclouds wrote: Hi, I have a function: post :: (ToJson p, FromJson q) => String -> String -> String -> Map.Map String p -> IO q Now I'd like to call it like: r<- post site token "user.addMedia" (Map.fromList [ ("users", users :: ToJson)

[Haskell-cafe] Fwd: Re: How to select last inserted record from Table Using Database.HSQL.MySQL

Forwarding to list Original Message Subject:Re: [Haskell-cafe] How to select last inserted record from Table Using Database.HSQL.MySQL Date: Tue, 26 Jul 2011 14:27:56 +0300 From: Sergiy Nazarenko To: Steffen Schuldenzucker Thanx a lot! I could solve that

Re: [Haskell-cafe] How to select last inserted record from Table Using Database.HSQL.MySQL

Hello Sergiy, On 07/25/2011 04:54 PM, Sergiy Nazarenko wrote: Hi, everyone! trycon <- connect "mysql" "bigtables" "vasya" "***" stmt' <- query trycon "INSERT INTO mytable (user,time,host,) VALUES ("Vasya","2011.07.30 11.59","foo")" I am beginner to use HSQL and I have a problem. I need to

Re: [Haskell-cafe] Make Show instance

Hi. On 07/21/2011 04:45 PM, Александр wrote: Hello, I have binary tree, with every leaf tuple - (k,v): data Tree k v = EmptyTree | Node (k, v) (Tree k v) (Tree k v) How can i make Show Instance for (Tree Int Int) ? The easiest way is automatic derivation: data Tree k v = EmptyTree | Nod

Re: [Haskell-cafe] pointer equality

On 07/21/2011 02:15 PM, Alexey Khudyakov wrote: Any examples for hangups of 'smartEq' are greatly appreciated, I couldn't produce any so far. Following sequences will hang smartEq. They are both infinite and aperiodic. smartEq (fromList primes) (fromList primes) smartEq (fromList pidigits)

Re: [Haskell-cafe] pointer equality

On 07/21/2011 10:30 AM, Pedro Vasconcelos wrote: On Wed, 20 Jul 2011 12:48:48 -0300 Thiago Negri wrote: Is it possible to implement (==) that first check these thunks before evaluating it? (Considering both arguments has pure types). E.g., Equivalent thunks, evaluates to True, does not ne

Re: [Haskell-cafe] Type checking oddity -- maybe my own confusion

On 07/12/2011 05:01 PM, Ryan Newton wrote: Hi all, Is there something wrong with the code below? My anticipation was that the type of "test" would include the class constraint, because it uses the Assign constructor. But if you load this code in GHCI you can see that the inferred type was "tes

Re: [Haskell-cafe] class and instance

On 07/10/2011 12:49 PM, Patrick Browne wrote: Hi, I am trying to understand the following code. I have written my current (mis-)understanding and questions below. I do not wish to improve the code, it is from a research paper[1] that I am trying to understand. Pat [1] ftp://ftp.geoinfo.tuwien.ac

Re: [Haskell-cafe] Arrow instance of function type [a] -> [b]

Hi Markus, On 07/06/2011 03:04 PM, Markus Läll wrote: [...] import Control.Arrow import Control.Category type X a b = [a] -> [b] instance Category X where id = map Prelude.id g . f = g Prelude.. f instance Arrow X where arr f = map f first f = unzip>>> first f>>> uncurry

Re: [Haskell-cafe] overloading show function

Hi Philipp, On 06/29/2011 11:50 PM, Philipp Schneider wrote: Hi cafe, in my program i use a monad of the following type newtype M a = M (State -> (a, State)) btw., it looks like you just rebuilt the State monad. ... instance (Show a,Show b) => Show (M (a,b)) where show (M f) = let

Re: [Haskell-cafe] Fwd: Re: Period of a sequence

Michael, On 06/27/2011 01:51 PM, Steffen Schuldenzucker wrote: > > Forwarding to -cafe > > Original Message > Subject: Re: [Haskell-cafe] Period of a sequence > Date: Mon, 27 Jun 2011 04:46:10 -0700 (PDT) > From: michael rice > To: Steffen Schuld

[Haskell-cafe] Fwd: Re: Period of a sequence

Forwarding to -cafe Original Message Subject:Re: [Haskell-cafe] Period of a sequence Date: Mon, 27 Jun 2011 04:46:10 -0700 (PDT) From: michael rice To: Steffen Schuldenzucker Hi Steffen, Repeating decimals. 5/7 == 0.714285 714285 7142857 ... Period = 6

Re: [Haskell-cafe] Period of a sequence

On 06/26/2011 04:16 PM, michael rice wrote: MathWorks has the function seqperiod(x) to return the period of sequence x. Is there an equivalent function in Haskell? Could you specify what exactly the function is supposed to do? I am pretty sure that a function like seqPeriod :: (Eq a) => [a

[Haskell-cafe] Fwd: Re: Hackage Server not reachable

Forwarding to -cafe. Original Message Subject:Re: [Haskell-cafe] Hackage Server not reachable Date: Wed, 22 Jun 2011 20:43:59 +1000 From: Stuart Coyle To: Steffen Schuldenzucker Cabal fails with a timeout like this: stuart@Panforte:~/Code/gift-parser

Re: [Haskell-cafe] Hackage Server not reachable

On 06/22/2011 11:02 AM, Stuart Coyle wrote: I cannot reach the hackage server so cabal can't download packages. Have I the correct address? http://hackage.haskell.org Yes. stuart@rumbaba:~# resolveip hackage.haskell.org IP address of hackage.haskell.org

Re: [Haskell-cafe] Are casts required?

Hi Patrick, On 06/06/2011 09:45 AM, Patrick Browne wrote: Are casts required to run the code below? If so why? Thanks, Pat -- Idetifiers for objects class (Integral i) => IDs i where startId :: i newId :: i -> i newId i = succ i sameId, notSameId :: i -> i -> Bool -- Assertion is

Re: [Haskell-cafe] Comment Syntax

Am 03.06.2011 10:32, schrieb Guy: What might --| mean, if not a comment? It doesn't seem possible to define it as an operator. Obviously, anyone who is going to write a formal logic framework would want to define the following operators ;) : T |- phi: T proves phi T |-- phi: T proves phi dir

Re: [Haskell-cafe] Server hosting

On 05/06/2011 08:07 PM, Andrew Coppin wrote: [...] I currently have a website, but it supports only CGI *scripts* (i.e., Perl or PHP). It does not support arbitrary CGI *binaries*, which is what I'd want for Haskell. In fact, I don't have control over the web server at all; I just put content on

Re: [Haskell-cafe] A small Darcs anomoly

On 04/28/2011 05:23 PM, malcolm.wallace wrote: Unfortunately, sharing a build directory between separate repositories does not work. After a build from one repository, all the outputs from that build will have modification times more recent than all the files in the other repository. Then I sug

Re: [Haskell-cafe] Generating random graph

Hello. I don't know if that is the reason for the strange behaviour, but On 04/11/2011 03:03 AM, Mitar wrote: I have made this function to generate a random graph for Data.Graph.Inductive library: generateGraph :: Int -> IO (Gr String Double) generateGraph graphSize = do when (graphSize<

Re: [Haskell-cafe] object oriented technique

Tad, It doesn't look bad, but depending on what you want to do with the [ShapeD] aftewards you might not need this level of generality. Remember that the content of a ShapeD has type (forall a. ShapeC a => a), so all you can do with it is call class methods from ShapeC. So if all you do is cons

Re: [Haskell-cafe] Having trouble with instance context

Hi, On 02/23/2011 04:40 PM, Kurt Stutsman wrote: > [...] > Test is actually a kind of Serializable class. I don't want to restrict it to only working with Enums, which is what your OverlappingInstances seems to address. Is there a better way for doing what I am trying to do? Example: impor

Re: [Haskell-cafe] Proving correctness

On 02/11/2011 12:06 PM, C K Kashyap wrote: [...] I know that static typing and strong typing of Haskell eliminate a whole class of problems - is that related to the proving correctness? [...] You might have read about "free theorems" arising from types. They are a method to derive certain prop

Re: [Haskell-cafe] Synthetic values?

In ghci I get >>> let evil = appendLog "Foo" "Bar" :1:11: Ambiguous type variable `p' in the constraints: `PRead p' arising from a use of `appendLog' at :1:11-31 `PWrite p' arising from a use of `appendLog' at :1:11-31 Probable fix: add a type signature that f

Re: [Haskell-cafe] Extending GHCi

On 02/07/2011 12:45 PM, C K Kashyap wrote: $ ghci GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ff

Re: [Haskell-cafe] Extending GHCi

Ok, so someFunction should modify the server's configuration? Maybe you can model it with an IORef like this (untested!): > import Data.IORef > > type Config = String -- String to be prepended to every answer > > someFunction :: String -> IORef Config -> IORef Config > someFunction s r = modi

Re: [Haskell-cafe] Extending GHCi

On 02/04/2011 12:36 PM, C K Kashyap wrote: Hi, I am looking for a way to extend GHCI such that I can do something like this $ ghci GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loa

Re: [Haskell-cafe] ($) not as transparent as it seems

Thanks to all of you for making GHC's behaviour yet a bit clearer to me. On 02/03/2011 11:25 PM, Daniel Fischer wrote: On Thursday 03 February 2011 23:03:36, Luke Palmer wrote: This is probably a result of strictness analysis. error is technically strict, so it is reasonable to optimize t

[Haskell-cafe] ($) not as transparent as it seems

Dear cafe, does anyone have an explanation for this?: >>> error (error "foo") *** Exception: foo >>> error $ error "foo" *** Exception: *** Exception: foo -- Steffen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mail

Re: [Haskell-cafe] Inheritance and Wrappers

On 01/31/2011 08:58 PM, MattMan wrote: [...] data Wrapper a = Wrap a instance (Num a) => AbGroup (Wrapper a) where add (Wrap i) (Wrap j) = Wrap(i+j) However, this is clumsy. Is there something else I can do? Thanks This is the normal approach. You can do funny things with the Overlapp

Re: [Haskell-cafe] Typing problem

Michael, just leaving out the type declaration for 'normalize', your module complies fine and ghc infers the following type: normalize :: (Integral a, Floating a) => [a] -> a -> a Note that the context (Integral a, Floating a) cannot be met by any of the standard types. (try in ghci: ":i In

Re: [Haskell-cafe] Instantiation problem

Hi, Your definition of 'unit' in the instance MetricDescription LengthInCentimetres Centimetre is not well-typed. Maybe you want to write either unit (LengthInCentimitres 2.0) = Centimetre -- (pattern match fail for all (LengthInCentimetres l), l /= 2.0) or unit l = Centimetre -- i.e. unit

Re: [Haskell-cafe] tricky recursive type instance method

Hi, you might want to take a look at [1]AdvancedOverlap. However, the most simple option would be to wrap up your (Real a => DAlgebra a a) instance in a newtype: > {-# LANGUAGE GeneralizedNewtypeDeriving #-} > > newtype FromReal a = FromReal a deriving (Eq, Ord, Read, Show, Num, Real) > >ins

Re: [Haskell-cafe] combined parsing & pretty-printing

On 01/26/2011 05:22 PM, Ozgur Akgun wrote: I working on a DSL represented by a algebraic data type with many constructors. I can write (separately) a parser and a pretty-printer for it, and I am doing so at the moment. However, this way it feels like repeating the same information twice. Is t

Re: [Haskell-cafe] Tool for evaluating "GHCi>" lines in a source file

On 01/23/2011 06:48 PM, Max Rabkin wrote: On Sun, Jan 23, 2011 at 12:35, Steffen Schuldenzucker wrote: Hi, some time ago I read of a small tool that extracts lines like "GHCi> some_expression" from a source file and appends GHCi's output to them. Now I can't fin

[Haskell-cafe] Tool for evaluating "GHCi>" lines in a source file

Hi, some time ago I read of a small tool that extracts lines like "GHCi> some_expression" from a source file and appends GHCi's output to them. Now I can't find it again. Does anyone remember its name? Thanks. Steffen ___ Haskell-Cafe mailing list

Re: [Haskell-cafe] Problem on overlapping instances

Am 05.01.2011 09:24, schrieb Magicloud Magiclouds: Hi, I am using Data.Binary which defined "instance Binary a => Binary [a]". Now I need to define "instance Binary [String]" to make something special for string list. How to make it work? I looked into the chapter of overlappinginstances,

Re: [Haskell-cafe] What is simplest extension language to implement?

On 11/02/2010 10:40 AM, Yves Parès wrote: Because he would have either to recompile the whole program or to use things like hint, both implying that GHC must be installed on the user side (600Mo+ for GHC 6.12.3) Isn't there a way to use some stripped-down version of ghc and the base libraries,

Re: [Haskell-cafe] Am I using type families well?

Hi Yves, On 11/01/2010 09:44 PM, Yves Parès wrote: > Yes, I did make a small mistake in the type of eval. > In fact, through the compiler messages, I guessed that it was a problem of > matching between the 'rsc' type variable of runLoader and the 'rsc' of eval. > I thought that this kind of matchi

Re: [Haskell-cafe] Finite but not fixed length...

Hmm, ok, I simplified the idea[1] and it looks like I'm getting the same problem as you when trying to drop the 'n' parameter carrying the length of the list. Sad thing. [1] http://hpaste.org/40538/finite_list__not_as_easy_as_i On 10/13/2010 10:43 AM, Steffen Schuldenzucker wrot

Re: [Haskell-cafe] Finite but not fixed length...

I don't know too much about GADTs, but it works fine with fundeps: http://hpaste.org/40535/finite_list_with_fundeps (This is rather a draft. If anyone can help me out with the TODOs, I'd be happy.) -- Steffen On 10/13/2010 10:40 AM, Eugene Kirpichov wrote: > Well, in my implementation it's i

Re: [Haskell-cafe] in-equality type constraint?

On 07/17/2010 03:50 AM, Gábor Lehel wrote: > Does "TypeEq a c HFalse" imply proof of inequality, or unprovability > of equality? Shouldn't these two be equivalent for types? > > On Sat, Jul 17, 2010 at 2:32 AM, Steffen Schuldenzucker > wrote: >> On 07/17/2

Re: [Haskell-cafe] in-equality type constraint?

On 07/17/2010 01:08 AM, Paul L wrote: > Does anybody know why the type families only supports equality test > like a ~ b, but not its negation? > This has annoyed me, too. However, HList provides something quite similar, namely the TypeEq[1] fundep-ed class which will answer type-equality with a

Re: [Haskell-cafe] Criteria for determining if a recursive function can be implemented in constant memory

Lennart Augustsson wrote: > Are you limiting your data structures to numbers? In that case, only > numbers of limited size, the answer is, of course, yes. You can > implement any such function in constant space and time. Just make a > lookup table. > > Sent from my iPad

Re: [Haskell-cafe] Criteria for determining if a recursive function can be implemented in constant memory

On 7/5/2010 8:33 PM, Andrew Coppin wrote: Tillmann Rendel wrote: Hi Steffen, Steffen Schuldenzucker wrote: Given the definition of a recursive function f in, say, haskell, determine if f can be implemented in O(1) memory. Constant functions are implementable in O(1) memory, but interpreters

Fwd: Re: [Haskell-cafe] Criteria for determining if a recursive function can be implemented in constant memory

Date: Tue, 6 Jul 2010 13:25:57 +1200 From: Richard O'Keefe To: Steffen Schuldenzucker On Jul 6, 2010, at 12:23 AM, Steffen Schuldenzucker wrote: Given the definition of a recursive function f in, say, haskell, determine if f can be implemented in O(1) memory. How are you s

[Haskell-cafe] Criteria for determining if a recursive function can be implemented in constant memory

Dear Cafe, since a little discussion with my tutor I am wondering how the following problem can be solved and if it is decidable: Given the definition of a recursive function f in, say, haskell, determine if f can be implemented in O(1) memory. First I thought the solution would be "check

Re: [Haskell-cafe] More experiments with ATs

On 07/04/2010 01:49 PM, Sjoerd Visscher wrote: > > On Jul 4, 2010, at 11:31 AM, Andrew Coppin wrote: > type family F f a :: * class RFunctor f where (%) :: f a b -> (a -> b) -> F f a -> F f b >> >> I have literally no idea what a type family is. I understand ATs (I think

Re: [Haskell-cafe] How to build an "Indicator Type" for a type class?

7;m gonna read the HList paper now... Best regards, Steffen > http://okmij.org/ftp/Haskell/types.html#class-based-dispatch > > -Brent > > On Mon, May 31, 2010 at 01:32:18PM +0200, Steffen Schuldenzucker wrote: >> Dear Cafe, >> >> let: >> >>&g

[Haskell-cafe] How to build an "Indicator Type" for a type class?

Dear Cafe, let: > data True > data False > > class C a (arbitrary instances for C may follow) Now, how to obtain an "Indicator Type" for C, i.e. a type IndC that is defined via a type family / fundep / ... , so that IndC a = True forall a which are instances of C IndC a = False for all othe

Re: [Haskell-cafe] Data creation pattern?

Hi. Stephen Tetley wrote: Hi Eugene Is something like this close to what you want: For example this builds an object with ordered strings... makeOrdered :: String -> String -> String -> Object makeOrdered a b c = let (s,t,u) = sort3 (a,b,c) in Object s t u Or just: makeOrdered a b c = le

Re: [Haskell-cafe] Ada-style ranges

On 04/26/2010 12:50 PM, hask...@kudling.de wrote: > > > Hi list, > > > > how would you describe Ada's ranges in Haskell's typesystem? > > http://en.wikibooks.org/wiki/Ada_Programming/Types/range Hi Lenny, can non-constant expressions be given as arguments to 'range'? If not, then what abou

Re: [Haskell-cafe] generalized newtype deriving allows the definition of otherwise undefinable functions

On 03/08/2010 10:45 PM, Wolfgang Jeltsch wrote: > The point is, of course, that such conversions are not only possible for > binary operations but for arbitrary values and that these conversions are > done > by a single generic function conv. I don’t think it would be possible to > implement co

Re: [Haskell-cafe] classes with types which are wrapped in

Hi Andrew, Andrew U. Frank wrote: here a simplistic case (i know that A could be reduced to [], my real cases are more complicated). data A b = A b [b] data Asup x ab y = Asup x ab y class X a b where push :: b -> a b -> a b instance X A Int where push b' (A b bs) = A b' (b:bs) ins

Re: [Haskell-cafe] lawless instances of Functor

Brent Yorgey wrote: > On Mon, Jan 04, 2010 at 11:49:33PM +0100, Steffen Schuldenzucker wrote: >> [...] > > As others have pointed out, this doesn't typecheck; but what it DOES > show is that if we had a type class > > class Endofunctor a where > efmap :: (a

Re: [Haskell-cafe] lawless instances of Functor

Hi Paul, Paul Brauner wrote: > Hi, > > I'm trying to get a deep feeling of Functors (and then pointed Functors, > Applicative Functors, etc.). To this end, I try to find lawless > instances of Functor that satisfy one law but not the other. > > I've found one instance that satisfies fmap (f.g) = f

Re: [Haskell-cafe] Partially applied functions

Ozgur Akgun wrote: > Hi cafe, > > Is such a thing possible, > > > add :: Int -> Int -> Int > add x y = x + y > > -- a list of partially applied functions > adds = [add 3, add 5, add 7, add 3, add 5, add 8] > > -- an example usage of the list > k = map (\ f -> f 10 ) adds > > add3s = filter (?

Re: [Haskell-cafe] What does the `forall` mean ?

Andrew Coppin wrote: > > I just meant it's not immediately clear how > > foo :: forall x. (x -> x -> y) > > is different from > > foo :: (forall x. x -> x) -> y Uhm, I guess you meant foo :: forall x. ((x -> x) -> y) VS. foo :: (forall x. x -> x) -> y , didn't you? __

Re: [Haskell-cafe] Ghci :ctags or hasktags print to standard out instead of file

> The TagList plugin for Vim reads the ctags info from the command line > instead of from the file. I could not figure out how to make ghci :ctags or > hasktasks to print the ctags info to the command line. Is there a way to > do that? Any hints? Hmm... some shell magic: mkfifo foo cat foo & ech

Re: [Haskell-cafe] Trying to Express Constraints using a data structure

On 16:25 Mon 18 May , Gü?nther Schmidt wrote: > Hi all, > > I'm trying to express a constraint using a data structure. > > Let's say I'd want to express a "mapping" of a to b, c to b, d to b and e > to f. > > A mapping can also be from a to a, b to b and so on. > > The constraint is that one c

Re: [Haskell-cafe] Haskell Arrows Applications

On 07:33 Wed 06 May , Hannousse wrote: > > Hello, > > I'm interested to the concept of arrows in Haskell, however, I couldn't find > a real application or example using this new technology in a real world > application. All what I found are just academic examples and other people > developing

Re: [Haskell-cafe] Re: Converting IO [XmlTree] to [XmlTree]

On 04:33 Tue 28 Apr , Matthew Gruen wrote: >On the other hand, here's an un-pure-able and un-point-able functor: > >instance Functor ((,) m) where >  --fmap :: (n -> n') -> (m, n) -> (m, n') >    fmap f (m, n) = (m, f n) >n -> (m, n) is not a function you can write in gener

Re: [Haskell-cafe] Re: Converting IO [XmlTree] to [XmlTree]

On 22:19 Mon 27 Apr , Martijn van Steenbergen wrote: > Tillmann Rendel wrote: >> Achim Schneider wrote: >>> In other words: >>> >>> 1) Explain Pointed >>> 2) Explain Functor >>> 3) Explain Applicative >>> 4) Explain Monad >> Why Pointed first? Functor seems more useful and more basic. > > They

[Haskell-cafe] Re: HXT: desperatedly trying to "concat"

Hello again. I finally got it myself. It was just a matter of parentheses: See http://hpaste.org/fastcgi/hpaste.fcgi/view?id=3229 for the corrected version. Looks like what I was trying to do is not expressable via just an arrow, one needs a function mapping the input arrow to a new one. I'm g

[Haskell-cafe] HXT: desperatedly trying to "concat"

Hi. I've got a problem with the Haskell XML Toolkit (hxt). I want to write a little app that performs REST requests from a certain (rather simple) XML format. A example procedure Call looks like testData defined below. What I'd like to do is to transform this xml tree into a GET variable string