On Dec 21, 2007 11:50 AM, Nicholls, Mark [EMAIL PROTECTED] wrote:
Now I have
module Main where
data SquareType numberType = Num numberType = SquareConstructor
numberType
This is a valid declaration, but I don't think it does what you want it to.
The constraint on numberType applies
On Dec 21, 2007 12:08 PM, Nicholls, Mark [EMAIL PROTECTED] wrote:
I thought from
Num numberType = SquareConstructor
numberType
We could deduce that (in English rather than get Haskell and FOL
confusion)
all values of SquareConstructor a….the type of a would have be be in
class
On Dec 21, 2007 12:47 PM, Nicholls, Mark [EMAIL PROTECTED] wrote:
Let me resend the code…as it stands….
*module* Main *where*
*data* SquareType numberType = Num numberType = SquareConstructor
numberType
*class* ShapeInterface shape *where*
area :: Num numberType =
On Dec 21, 2007 2:38 PM, Jules Bean [EMAIL PROTECTED] wrote:
David Menendez wrote:
That's a reasonable thing to assume. It just happens that Haskell
doesn't work that way. There's an asymmetry between constructing and
pattern-matching, and it's one that many people have complained about
On Dec 30, 2007 9:24 AM, Joost Behrends [EMAIL PROTECTED] wrote:
A similar point: The tutorials teach, that = has a similar meaning than
= in
mathematics. But there is a big difference: it is not reflexive. The
the right side is the definition of the left. Thus x=y has still some
kind of
On Jan 5, 2008 12:37 AM, Don Stewart [EMAIL PROTECTED] wrote:
The most notable change is the instance IsString for strict and
lazy bytestrings, enabling bytestrings to be written as direct string
literals, without needing 'pack'.
That is, the following is valid:
import
On Sun, Mar 21, 2010 at 11:31 PM, adamtheturtle kill2thr...@hotmail.com wrote:
So I have the code
shuffle :: Int - [a] - [a]
shuffle i [] = []
shuffle i cards = (cards!!i) : shuffle (fst pair) (delete (cards!!i) cards)
where pair = randomR (0, 51) (mkStdGen 42)
and it doesn't work, am I
On Fri, Mar 26, 2010 at 11:07 AM, Edward Kmett ekm...@gmail.com wrote:
On Fri, Mar 26, 2010 at 11:04 AM, Edward Kmett ekm...@gmail.com wrote:
-- as long as you're ignoring 'seq'
terminateSeq :: a - Unit
terminateSeq a = a `seq` unit
Er ignore that language about seq. a `seq` unit is
On Fri, Mar 26, 2010 at 8:20 PM, zaxis z_a...@163.com wrote:
In 6.12.1 under archlinux
let f x y z = x + y + z
:t f
f :: (Num a) = a - a - a - a
:t (=) . f
(=) . f :: (Num a) = a - ((a - a) - a - b) - a - b
((=) . f) 1 (\f x - f x) 2
5
In 6.10.4_1 under freebsd
let f x y z = x + y + z
On Fri, Mar 26, 2010 at 8:59 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
zaxis z_a...@163.com writes:
In 6.10.4_1 under freebsd
let f x y z = x + y + z
*Money :t f
f :: (Num a) = a - a - a - a
:t (=) . f
(=) . f :: (Monad ((-) a), Num a) = a - ((a - a) - a - b) - a - b
On Fri, Mar 26, 2010 at 9:13 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
David Menendez d...@zednenem.com writes:
On Fri, Mar 26, 2010 at 8:59 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
Some definitions and exports got changed, so in 6.12 the (- a) Monad
On Sat, Mar 27, 2010 at 12:56 AM, Thomas DuBuisson
thomas.dubuis...@gmail.com wrote:
Using bang patterns didn't help almost anything here. Using rem
instead of mod made the time go from 45s to 40s. Now, using -fvia-C
really helped (when I used rem but not using mod). It went down to
10s.
On Sat, Mar 27, 2010 at 1:45 PM, Tillmann Rendel
ren...@mathematik.uni-marburg.de wrote:
Jan-Willem Maessen wrote:
It's worth pointing out that there's a bit of bang-pattern mysticism going
on in this conversation (which has not been uncommon of late!). A non-buggy
strictness analyzer should
On Thu, Apr 1, 2010 at 5:27 AM, Jens Blanck jens.bla...@gmail.com wrote:
I was wondering if someone could give me some references to when and why the
choice was made to default integral numerical literals to Integer rather
than to Int in Haskell. Also, if you are aware of similar discussions in
On Sun, Apr 18, 2010 at 5:02 PM, wren ng thornton
w...@community.haskell.org wrote:
Heinrich Apfelmus wrote:
Anders Kaseorg wrote:
This concept can also be generalized to monad transformers:
class MonadTrans t = MonadTransMorph t where
morph :: Monad m = (forall b. (t m a - m b) - m b)
On Fri, Apr 23, 2010 at 10:11 PM, John Goerzen jgoer...@complete.org wrote:
Don Stewart wrote:
Oh, the Platform has very strict standards about APIs,
When a package may be added:
http://trac.haskell.org/haskell-platform/wiki/AddingPackages
That looks like a very solid document. Does it
On Sat, Apr 24, 2010 at 5:56 AM, Barak A. Pearlmutter ba...@cs.nuim.ie wrote:
Even deriving(Ord) only produces compare and relies on standard
definitions for other methods.
I don't think that's actually a problem. Surely the IEEE Floating
Point types would give their own definitions of not
On Mon, Apr 26, 2010 at 2:55 PM, Thomas van Noort tho...@cs.ru.nl wrote:
On 26-4-2010 20:12, Daniel Fischer wrote:
Am Montag 26 April 2010 19:52:23 schrieb Thomas van Noort:
...
Yes, y's type is more general than the type required by f, hence y is an
acceptable argument for f - even z ::
On Fri, May 7, 2010 at 10:26 PM, John Meacham j...@repetae.net wrote:
On Fri, May 07, 2010 at 08:27:04PM -0400, Dan Doel wrote:
Personally, I don't really understand why unfailable patterns were canned
(they don't seem that complicated to me), so I'd vote to bring them back, and
get rid of
On Sat, May 8, 2010 at 12:15 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
David Menendez d...@zednenem.com writes:
I wonder how often people rely on the use of fail in pattern matching.
Could we get by without fail or unfailable patterns?
ensureCons :: MonadPlus m = [a] - m
On Sat, May 8, 2010 at 1:16 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
David Menendez d...@zednenem.com writes:
On Sat, May 8, 2010 at 12:15 AM, Ivan Lazar Miljenovic
Well, any time you have a do-block like this you're using failable
patterns:
maybeAdd :: Maybe Int
On Mon, May 10, 2010 at 5:51 AM, Milind Patil milind_pa...@hotmail.com wrote:
For a function
f :: a - m b
f = undefined
I am having trouble understanding how the type of
(= f)
is
(= f) :: m a - m b
where, by definition, type of (=) is
(=) :: (Monad m) = m a - (a - m b) - m b
I
On Fri, May 21, 2010 at 3:56 AM, Max Bolingbroke
batterseapo...@hotmail.com wrote:
On 21 May 2010 01:58, Carlos Camarao carlos.cama...@gmail.com wrote:
But this type-correct program would become not typeable if
instances such as the ones referred to before (by Daniel Fischer)
I was thinking
2010/5/21 R J rj248...@hotmail.com:
Why does the following, trivial code snippet below hang GHCi when I type
Scalene Failure, and what's the fix?
An instance of Ord must declare compare or (=). You only defined (),
so () is using the default definition. Here are the defaults:
compare x y
On Thu, May 27, 2010 at 10:39 AM, Carlos Camarao
carlos.cama...@gmail.com wrote:
Isaac Dupree:
Your proposal appears to allow /incoherent/ instance selection.
This means that an expression can be well-typed in one module, and
well-typed in another module, but have different semantics in the
On Fri, Jun 18, 2010 at 12:44 PM, Heinrich Apfelmus
apfel...@quantentunnel.de wrote:
Sebastian Fischer wrote:
Edward Kmett wrote:
Sebastian Fischer wrote:
Heinrich Apfelmus wrote:
newtype CMaybe a = CMaybe (forall r. (a - Maybe r) - Maybe r)
Yes, with this type `orElse` has the same type as
On Mon, Jun 21, 2010 at 7:04 AM, Neil Brown nc...@kent.ac.uk wrote:
Here's my speculation, based on glancing at the libraries involved: I
believe the reason for this may be the MonadCatchIO instance for ContT:
===
instance MonadCatchIO m = MonadCatchIO (ContT r m) where
m `catch` f =
On Thu, Jun 24, 2010 at 3:08 AM, Ivan Miljenovic
ivan.miljeno...@gmail.com wrote:
As an aside, Alex Mason and I are discussing the possibility of taking
advantage of AusHack *shameless plug* to write some kind of classes
for the different types of containers with a hierarchy. I know about
On Fri, Jun 25, 2010 at 12:58 AM, Ivan Miljenovic
ivan.miljeno...@gmail.com wrote:
On 25 June 2010 14:41, David Menendez d...@zednenem.com wrote:
On Thu, Jun 24, 2010 at 3:08 AM, Ivan Miljenovic
ivan.miljeno...@gmail.com wrote:
As an aside, Alex Mason and I are discussing the possibility
On Sun, Jun 27, 2010 at 1:26 PM, Sebastian Fischer
s...@informatik.uni-kiel.de wrote:
Hi Max,
very interesting observations!
By the way, you can use this stuff to solve the restricted monad
problem (e.g. make Set an instance of Monad). This is not that useful
until we find out what the
On Thu, Jul 1, 2010 at 2:09 PM, Andrew Coppin
andrewcop...@btinternet.com wrote:
Consider the following:
class Path p where ...
class Path p = CompletePath p where ...
class Path p = IncompletePath p where
type CompletedPath p :: *
Obviously, the idea is that CompletedPath Foo
On Thu, Jul 1, 2010 at 2:35 PM, Christopher Lane Hinson
l...@downstairspeople.org wrote:
On Thu, 1 Jul 2010, Christopher Lane Hinson wrote:
Something like this should work:
class (Path p, CompletePath (CompletedPath p)) = IncompletePath p where
type CompletedPath p :: *
AIUI, this
On Sat, Jul 3, 2010 at 3:32 AM, Kevin Quick qu...@sparq.org wrote:
On Wed, 23 Jun 2010 00:14:03 -0700, Simon Peyton-Jones
simo...@microsoft.com wrote:
I'm interested in situations where you think fundeps work and type
families don't. Reason: no one knows how to make fundeps work cleanly with
On Sat, Jul 3, 2010 at 7:20 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
Serguey Zefirov sergu...@gmail.com writes:
I cannot directly create my own class instances for them because of
that. But I found that I can write Template Haskell code that could do
that - those data types
On Sun, Jul 11, 2010 at 3:25 PM, d...@patriot.net wrote:
Prelude Haskore :l Haskore
no location info: module `Haskore' is a package module
Failed, modules loaded: none.
You need to use :m here.
--
Dave Menendez d...@zednenem.com
http://www.eyrie.org/~zednenem/
On Sat, Jul 17, 2010 at 2:10 PM, Don Stewart d...@galois.com wrote:
andrewcoppin:
Don Stewart wrote:
allbery:
like to repeat one request: Please, please, please make it easier to
- Download older versions of HP.
- Find out which HP release contains what.
- Figure out what the difference
2010/7/25 Eugeny N Dzhurinsky b...@redwerk.com:
Hello, everybody!
I am trying to develop some sort of library, which supposed to sign into a WEB
service, then perform some requests with it.
Initially I designed methods in the following way
data DServError = InvalidCredentials |
Neil Mitchell writes:
We should avoid referring to $PATH as the path, since we
already have FilePath.
Agreed, but I couldn't come up with a better name, if anyone has any
suggestions.
searchPath?
--
David Menendez [EMAIL PROTECTED] http://www.eyrie.org/~zednenem
something like,
class (Functor s, MonadPlus s, forall a. Sequence (s a) a) =
SeqFunctor s where
...
--
David Menendez [EMAIL PROTECTED] | In this house, we obey the laws
http://www.eyrie.org/~zednenem |of thermodynamics
want to
start writing if x Eq/== y Num/+ 1 then ... ?
--
David Menendez [EMAIL PROTECTED] | In this house, we obey the laws
http://www.eyrie.org/~zednenem |of thermodynamics!
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http
because Control.Monad.State belongs to the MTL which is
outside Prelude.
On the other hand, if you are using MTL, you'd probably want a more
general signature, like:
(RandomGen g, MonadState g m) = m a
--
David Menendez [EMAIL PROTECTED] | In this house, we obey the laws
http://www.eyrie.org
diff (Pt x y) (Pt x' y') = Vec (x - x') (y - y')
midpoint p1 p2 = add (mult 0.5 (diff p1 p2)) p2
The type of midpoint is something like
(DivisionRing a, Module a b, SymmetricGroupAction b c) = c - c - c
--
David Menendez [EMAIL PROTECTED] | In this house, we obey the laws
http://www.eyrie.org
Ross Paterson writes:
On Thu, Sep 14, 2006 at 01:11:56AM -0400, David Menendez wrote:
Coincidentally, I spent some time last week thinking about a
replacement for the Num class. I think I managed to come up with
something that's more flexible than Num, but still mostly
comprehensible
not to print the missing component messages
by default. There could be a verbose option to turn them back on.
--
David Menendez [EMAIL PROTECTED] | In this house, we obey the laws
http://www.eyrie.org/~zednenem |of thermodynamics!
___
Haskell-Cafe
On Jan 20, 2008 12:56 AM, Thomas Hartman [EMAIL PROTECTED] wrote:
The code below compiles as given, however if I uncomment the tSM
function I get the overlapping instance error mentioned in the subject
line.
Can someone give me advice on how to do what I want to do?
basically I want to
On Jan 22, 2008 6:19 PM, Chad Scherrer [EMAIL PROTECTED] wrote:
A lazy ByteString is an alternative to a String=[Char]
Careful. ByteString is an alternative to [Word8]. Converting [Char] to
ByteString and back requires an encoding. (Unfortunately, the only encoding
that comes with the
On Jan 23, 2008 12:20 PM, Valery V. Vorotyntsev [EMAIL PROTECTED] wrote:
I've built GHC from darcs, and...
Could anybody tell me, what's the purpose of Arrow[1] not having `'
method?
It's derived from the Category superclass.
--
Dave Menendez [EMAIL PROTECTED]
On Feb 6, 2008 6:32 AM, Bas van Dijk [EMAIL PROTECTED] wrote:
Is there a way to 'invert' an arbitrary Monad?
By 'inverting' I mean to turn success into failure and failure into
success. Here are some specific inversions of the Maybe and List
Monad:
invM :: Maybe a - Maybe ()
invM Nothing
On Feb 13, 2008 5:36 AM, Luke Palmer [EMAIL PROTECTED] wrote:
On Feb 13, 2008 9:33 AM, [EMAIL PROTECTED] wrote:
The approach is based on the final tagless representation. Here is our
DSL:
class Exp repr where
constant :: Int - repr Int
variable :: String - repr Int
add
On Feb 19, 2008 4:15 PM, Wolfgang Jeltsch [EMAIL PROTECTED] wrote:
Am Dienstag, 19. Februar 2008 18:26 schrieben Sie:
[…]
However, I was told this: ~ a b is a ~ b, but if I write c a b and
wish the effect of a `c` b. This would not work. ~ as an infix operator
has a special place in
On Wed, Feb 20, 2008 at 10:46 PM, [EMAIL PROTECTED] wrote:
Quoting Neil Mitchell [EMAIL PROTECTED]:
Yes, its the projection onto another type:
[] = Nothing
(x:xs) = Just (x, xs)
Also known as msplit:
http://www.haskell.org/haskellwiki/New_monads/MonadSplit
Almost. The
On Thu, Feb 21, 2008 at 12:54 PM, Yitzchak Gale [EMAIL PROTECTED] wrote:
Duncan Coutts wrote:
To be honest I like the fact that haddock's markup is really simple and
perhaps somewhat restrictive. A great improvement though would be...
a generic backend that spits out
the info that
On Thu, Mar 6, 2008 at 3:57 PM, ChrisK [EMAIL PROTECTED] wrote:
Okay, I get the difference.
The T a annotation in val :: T a)and val :: T a does not help choose
the
C a dictionary.
But the val :: a- T a and val (undefined :: a) allows a to
successfully
choose the C a dictionary.
On Thu, Mar 6, 2008 at 9:52 PM, Ryan Ingram [EMAIL PROTECTED] wrote:
This is actually a general issue with the way typeclasses are defined
in Haskell; the accepted solution is what the Show typeclass does:
class C a where
c :: a
cList :: [a]
cList = [c,c]
instance C
On Fri, Mar 7, 2008 at 2:10 AM, Ryan Ingram [EMAIL PROTECTED] wrote:
I don't think the cost is that great; the compiler can easily flag
polymorphic functions that require type information for some or all
arguments and in many cases the type evidence can be passed
just-in-time when calling
On Wed, Mar 12, 2008 at 7:48 PM, [EMAIL PROTECTED] wrote:
Adrian Hey wrote:
This might be a reasonable thing to say about *sortBy*, but not sort
as the ordering of equal elements should not be observable (for any
correct instance of Ord). It should be impossible to implement a
On Wed, Mar 12, 2008 at 4:29 PM, Aaron Denney [EMAIL PROTECTED] wrote:
When defining max, yes, you must take care to make sure it useable for
cases when Eq is an equivalence relation, rather than equality.
If you're writing library code, then it won't generally know whether
Eq means true
On Fri, Mar 14, 2008 at 2:50 PM, Andrew Coppin
[EMAIL PROTECTED] wrote:
Haskell has an expressive and powerful type system - which I love. It
also has a seemingly endless list of weird and obscure type system
extensions. And there are various things you can do in Haskell which
*require*
On Mon, Mar 24, 2008 at 12:14 AM, Manuel M T Chakravarty
[EMAIL PROTECTED] wrote:
One difference between type families and (value-level) functions is
that not all parameters of a type family are treated the same. A type
family has a fixed number of type indicies. We call the number of
On Fri, Apr 4, 2008 at 5:45 PM, Don Stewart [EMAIL PROTECTED] wrote:
ndmitchell:
Note: In case anyone gets the wrong impression, I am not suggesting
lazy naturals be the standard numeric type in Haskell, just that by
not going that way we have paid a cost in terms of elegance.
I'd
On Mon, Apr 21, 2008 at 2:18 PM, John Goerzen [EMAIL PROTECTED] wrote:
Back when I was working on the logic for the bin-packing solver that I added
to MissingH (for use with datapacker), I had a design decision to make: do I
raise runtime errors with the input using error, or do I use an
On Tue, Apr 22, 2008 at 11:57 AM, Aaron Tomb [EMAIL PROTECTED] wrote:
On Apr 22, 2008, at 6:20 AM, John Goerzen wrote:
* xml
A simple, lightweight XML parser/generator.
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xml
Can you describe how this
On Fri, Apr 25, 2008 at 3:45 PM, Dan Weston [EMAIL PROTECTED] wrote:
Is there a Haskell Wiki page (or blog) on Monad Suspension? This looks like
a nice paradigm that apfelmus points out can be used to considerably
shorten your code, but only if the rest of us learn how!
There are a few papers
On Thu, May 1, 2008 at 4:10 PM, Daniil Elovkov
[EMAIL PROTECTED] wrote:
Felipe Lessa wrote:
On Thu, May 1, 2008 at 9:44 AM, Felipe Lessa [EMAIL PROTECTED]
wrote:
On Thu, May 1, 2008 at 9:32 AM, Edsko de Vries [EMAIL PROTECTED]
wrote:
So then the question becomes: what *is* the
On Sat, May 3, 2008 at 12:30 PM, Edsko de Vries [EMAIL PROTECTED] wrote:
I think Huet's Zipper is intended to solve this sort of problem.
data Path = Top | BranchL Path Tree | BranchR Tree Path
type Zipper = (Path, Tree)
openZipper :: Tree - Zipper
openZipper t =
On Tue, May 13, 2008 at 9:06 PM, Ronald Guida [EMAIL PROTECTED] wrote:
I have a few questions about commutative monads and applicative functors.
From what I have read about applicative functors, they are weaker than
monads because with a monad, I can use the results of a computation to
On Sat, May 17, 2008 at 1:24 AM, Kim-Ee Yeoh [EMAIL PROTECTED] wrote:
Dan Piponi-2 wrote:
In fact, you can use the Reader monad as a fixed size container monad.
Interesting that you say that. Reader seems to me more as an anti-container
monad.
You just have to think of the environment as
2008/5/22 Olivier Boudry [EMAIL PROTECTED]:
On Wed, May 21, 2008 at 6:19 PM, Dmitri O.Kondratiev [EMAIL PROTECTED]
wrote:
-- Then we can use this State object (returned by getAny) in a function
generating random values such as:
makeRnd :: StdGen - (Int, StdGen)
makeRnd = runState (do
2008/6/25 Conal Elliott [EMAIL PROTECTED]:
I have a foggy memory that early ML had only binary pairing, nesting for
n-tuples. Can anyone confirm this memory. If so, does anyone remember the
rationale for going to n-tuples? Performance, perhaps?
Similarly, did the Haskell designers consider
On Wed, Jul 9, 2008 at 1:03 AM, wren ng thornton [EMAIL PROTECTED] wrote:
What I would like to see is the ability to do (1) module renaming, (2)
qualified import, (3) unqualified import, and (4) hiding all in a single
declaration with a regular syntax. For example:
import Data.Map as Map
On Wed, Jul 9, 2008 at 2:51 PM, Jason Dusek [EMAIL PROTECTED] wrote:
David Menendez [EMAIL PROTECTED] wrote:
I've often thought it would be for Haskell to steal Agda's
module syntax. It does pretty much everything you want (plus
some other stuff we maybe don't need) and the various things
2009/10/5 Robert Atkey bob.at...@ed.ac.uk:
Hi Günther,
The underlying problem with the implementation of 'lam' is that
you have to pick an evaluation order for the side effects you want in
the semantics of your embedded language. The two obvious options are
call-by-name and call-by-value.
I
On Mon, Oct 5, 2009 at 7:56 PM, Floptical Logic flopticalo...@gmail.com wrote:
The code below is a little interactive program that uses some state.
It uses StateT with IO to keep state. My question is: what is the
best way to generalize this program to work with any IO-like
monad/medium? For
On Mon, Oct 5, 2009 at 11:54 PM, Floptical Logic
flopticalo...@gmail.com wrote:
Instead of specifying the monad implementation, specify the interface.
That is, you are using state operations (from MonadState) and IO
operations (from MonadIO). Try removing all the type signatures that
mention
On Tue, Oct 6, 2009 at 2:49 PM, Gregory Collins g...@gregorycollins.net wrote:
Arne Dehli Halvorsen arne@gmail.com writes:
This may be a little off-topic, but if someone could help me, I'd be
grateful.
I am trying to get to a working gtk2hs environment in MacOSX Snow Leopard
Have you
On Wed, Oct 7, 2009 at 12:08 PM, Ben Franksen ben.frank...@online.de wrote:
More generally, any ring with multiplicative unit (let's call it 'one') will
do.
Isn't that every ring? As I understand it, the multiplication in a
ring is required to form a monoid.
--
Dave Menendez
On Wed, Oct 7, 2009 at 8:29 PM, Michael Mossey m...@alumni.caltech.edu wrote:
In Test.QuickCheck, the type of 'generate' is
generate :: Int - StdGen - Gen a - a
I can't find docs that explain what the Int does. Some docs are here:
On Fri, Oct 9, 2009 at 11:12 AM, Felipe Lessa felipe.le...@gmail.com wrote:
On Thu, Oct 08, 2009 at 12:54:14AM -0700, o...@okmij.org wrote:
Actually it is possible to implement all three evaluation orders
within the same final tagless framework, using the same interpretation
of types and
On Fri, Oct 9, 2009 at 1:39 PM, Felipe Lessa felipe.le...@gmail.com wrote:
On Fri, Oct 09, 2009 at 01:27:57PM -0400, David Menendez wrote:
On Fri, Oct 9, 2009 at 11:12 AM, Felipe Lessa felipe.le...@gmail.com wrote:
That's really nice, Oleg, thanks! I just wanted to comment that
I'd prefer
On Fri, Oct 9, 2009 at 6:47 PM, staafmeister g.c.stave...@uu.nl wrote:
Daniel Peebles wrote:
I vaguely remember on IRC someone pointing out that the Parsec monad
broke one of the laws. I think return _|_ x === _|_ which could be
causing your problem. I may be wrong though.
Confirmed,
On Sat, Oct 17, 2009 at 3:21 PM, Andrew Coppin
andrewcop...@btinternet.com wrote:
Suppose we have
newtype Foo x
instance Monad Foo
runFoo :: Foo x - IO x
What sort of things can I do to check that I actually implemented this
correctly? I mean, ignoring what makes Foo special for a
On Thu, Oct 22, 2009 at 2:23 AM, Gregory Crosswhite
gcr...@phys.washington.edu wrote:
For clarity, one trick that uses unsafePerformIO which you may have seen
posted on this list earlier today is the following way of creating a
globally visible IORef:
import Data.IORef
import
On Fri, Oct 30, 2009 at 12:59 PM, Luke Palmer lrpal...@gmail.com wrote:
On Fri, Oct 30, 2009 at 10:39 AM, Tom Davie tom.da...@gmail.com wrote:
Of note, there is a sensible monad instance for zip lists which I *think*
agrees with the Applicative one, I don't know why they're not monads:
On Fri, Oct 30, 2009 at 1:33 PM, Yusaku Hashimoto nonow...@gmail.com wrote:
Thanks for fast replies! Examples you gave explain why all
Applicatives are not Monads to me.
And I tried to rewrite Bob's Monad instance for ZipList with (=).
import Control.Applicative
instance Monad ZipList
On Sat, Oct 31, 2009 at 6:22 AM, Heinrich Apfelmus
apfel...@quantentunnel.de wrote:
Dan Weston wrote:
Can you elaborate on why Const is not a monad?
return x = Const x
fmap f (Const x) = Const (f x)
join (Const (Const x)) = Const x
This is not Const , this is the Identity monad.
The
On Sun, Nov 1, 2009 at 11:09 AM, b1g3ar5 nick.st...@gmail.com wrote:
OK, I understand that now but I've got a supplimentary question.
If I put:
instance Eq b = Eq (a - b) where
(==) = liftA2 (Prelude.==)
You don't need the Prelude. here.
to do the Eq part I get another error:
On Sun, Nov 1, 2009 at 7:12 AM, Heinrich Apfelmus
apfel...@quantentunnel.de wrote:
Even then, the results are mixed. The Church-encoding shines in GHCi as
it should, but loses its advantage when the code is being compiled. I
guess we have to look at the core if we want to know what exactly is
On Sun, Nov 1, 2009 at 11:20 AM, Conor McBride
co...@strictlypositive.org wrote:
On 31 Oct 2009, at 10:39, Conor McBride wrote:
On 30 Oct 2009, at 16:14, Yusaku Hashimoto wrote:
Hello cafe,
Do you know any data-type which is Applicative but not Monad?
[can resist anything but temptation]
On Sun, Nov 1, 2009 at 12:31 PM, Heinrich Apfelmus
apfel...@quantentunnel.de wrote:
David Menendez wrote:
On Sun, Nov 1, 2009 at 7:12 AM, Heinrich Apfelmus
apfel...@quantentunnel.de wrote:
Even then, the results are mixed. The Church-encoding shines in GHCi as
it should, but loses its
On Thu, Nov 5, 2009 at 4:34 PM, Andrew Coppin
andrewcop...@btinternet.com wrote:
Nicolas Pouillard wrote:
Excerpts from Neil Brown's message of Tue Nov 03 13:45:42 +0100 2009:
Hi,
I was thinking about some of my code today, and I realised that where I
have an arrow in my code, A b c, the
On Wed, Nov 11, 2009 at 1:09 PM, Matthew Pocock
matthew.poc...@ncl.ac.uk wrote:
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
On Fri, Nov 13, 2009 at 3:26 PM, Andy Gimblett hask...@gimbo.org.uk wrote:
First a type family where the type Y is functionally dependent on
the type X, and we have a function from Y to ().
class X a where
type Y a
enact :: Y a - ()
This is ambiguous. Type families are not injective
On Fri, Nov 13, 2009 at 4:00 PM, Daniel Fischer
daniel.is.fisc...@web.de wrote:
Am Freitag 13 November 2009 21:36:59 schrieb David Menendez:
I recall seeing a discussion of this in the GHC documentation, but I
can't seem to locate it.
Perhaps
http://www.haskell.org/haskellwiki/GHC
On Tue, Nov 17, 2009 at 6:31 PM, Ezra Lalonde ezra.lalo...@gmail.com wrote:
Using the same basic structure you did, and foldr, I think below is the
simplest method:
import Data.Maybe
searchList :: (a - Bool) - [a] - Maybe [a]
searchList p xs = foldr (\x acc - if p x
On Tue, Nov 17, 2009 at 10:01 PM, Luke Palmer lrpal...@gmail.com wrote:
filter even [0..] -- [0,2,4,6,8,...]
searchList even [0...] -- Just [0,2,4,6,8,...]
searchList gives Nothing in exactly those cases that filter gives [].
They give _|_ in exactly the same situations. searchList
On Wed, Nov 18, 2009 at 4:12 PM, Edward Kmett ekm...@gmail.com wrote:
Qualified imports are some times problematic when you need to work with
classes from the module. You can't define a member of two instances from
different two modules that define classes with conflicting member names.
This
On Wed, Nov 25, 2009 at 6:28 AM, Neil Brown nc...@kent.ac.uk wrote:
It looks like a bug to me. Can you show an exact list of nodes and edges
that is causing mkGraph to fail? Or is that what you have displayed, and I
can't parse it properly?
From what I can tell, insEdge inserts an edge
On Wed, Nov 25, 2009 at 11:02 AM, Neil Brown nc...@kent.ac.uk wrote:
David Menendez wrote:
From what I can tell, insEdge inserts an edge between two nodes which
are already in the graph. The code is calling insEdge on
arbitrarily-labeled nodes, which may not exist in the graph.
That's what
On Thu, Nov 26, 2009 at 3:47 PM, Antoine Latter aslat...@gmail.com wrote:
Lets say I want to provide an alternate or additional library of monad
transformer data types. To make these types maximally useful, they
should implement the typeclasses in the mtl package and in the
monads-tf package.
On Sun, Nov 29, 2009 at 8:37 AM, Duncan Coutts
duncan.cou...@googlemail.com wrote:
On Thu, 2009-11-26 at 16:40 -0500, David Menendez wrote:
The problem with this solution is that it doesn't scale. If we have M
packages providing types and N packages providing classes, then we
need M*N
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