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
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]
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
, 2013 at 12:23 AM, Steffen Schuldenzucker
sschuldenzuc...@uni-bonn.de 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
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
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.
Credits
---
Created by Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de
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:
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:
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
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
On 01/14/2012 03:55 PM, Ketil Malde wrote:
Bryan O'Sullivanb...@serpentine.com 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.
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
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
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 WalkableBinTree n
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
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 second
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
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)
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 nazarenko.ser...@gmail.com
To: Steffen Schuldenzucker sschuldenzuc
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 know row ID
On 07/21/2011 10:30 AM, Pedro Vasconcelos wrote:
On Wed, 20 Jul 2011 12:48:48 -0300
Thiago Negrievoh...@gmail.com 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
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)
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
|
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 test
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]
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 zip
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
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) =
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 nowg...@yahoo.com
To: Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de
Hi Steffen,
Repeating decimals.
5/7
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 nowg...@yahoo.com
To: Steffen Schuldenzucker sschuldenzuc
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 http://hackage.haskell.org
IP address of hackage.haskell.org
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 stuart.co...@gmail.com
To: Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de
Cabal fails with a timeout
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 not
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
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
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
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
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
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:
import
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
In ghci I get
let evil = appendLog Foo Bar
interactive:1:11:
Ambiguous type variable `p' in the constraints:
`PRead p'
arising from a use of `appendLog' at interactive:1:11-31
`PWrite p'
arising from a use of `appendLog' at interactive:1:11-31
Probable fix:
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
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.
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 = modifyIORef
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
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
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
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
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
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
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
On 01/23/2011 06:48 PM, Max Rabkin wrote:
On Sun, Jan 23, 2011 at 12:35, Steffen Schuldenzucker
sschuldenzuc...@uni-bonn.de 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 find
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,
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,
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 matching
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
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 wrote:
I don't
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
sschuldenzuc...@uni-bonn.de wrote:
On 07/17/2010 01:08 AM, Paul L
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
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
On Jul 6, 2010, at 6:37, Steffen Schuldenzucker
sschuldenzuc...@uni
: Tue, 6 Jul 2010 13:25:57 +1200
From: Richard O'Keefe o...@cs.otago.ac.nz
To: Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de
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
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
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
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!),
but TFs make no
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:
data True
data False
class C a
(arbitrary instances for C may follow)
Now, how
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 other a.
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 = let
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 about a
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 conv
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)
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 - a) - f a - f a
then it would
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) = fmap f
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 (?) adds -- add3s =
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?
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 echo
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 cannot map a
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 new
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 are in order of power:
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 general
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
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
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