On Mon, Dec 22, 2008 at 2:31 PM, Brian Hurt bh...@spnz.org wrote:
But I'm wondering why it's not in the standard library. The standards
committee just hasn't gotten around to it yet? Or was there some discussion
of this in the past on some (public) maillist, that my admittedly shallow
On Sun, Dec 14, 2008 at 2:38 PM, Don Stewart d...@galois.com wrote:
ketil:
Nice. For some more hubris, replace 'A' with 'The'.
I had the very same thought :)
It certainly wouldn't do to let, say, the existence of Concurrent
Clean get in the way of our self-promotion.
/g
--
I am in here
On Wed, Nov 26, 2008 at 1:54 PM, Miguel Mitrofanov
[EMAIL PROTECTED] wrote:
Maybe it'd be more intuitive if written backwards:
AppEq f a = (Applicative f, Eq a)
or even
AppEq f a = (Applicative f, Eq a)
The first is good, the second isn't. The first says the right thing:
if you can prove
On Tue, Nov 18, 2008 at 1:38 AM, Reiner Pope [EMAIL PROTECTED] wrote:
ATs are Associated Types, aka Type Families. They can be found in
the GHC 6.10 manual here:
http://haskell.org/ghc/docs/6.10.1/html/users_guide/type-families.html
As a starting point, you might want to try something like:
On Mon, Nov 17, 2008 at 10:38 AM, Maurício [EMAIL PROTECTED] wrote:
newtype ComplexWithDouble = ComplexWithDouble (ComplexNumber Double)
deriving ...
Perhaps you want something like:
class Complex r c | c - r
where makeComplex :: r - r - c
realPart :: c - r
imagPart
On Sun, Nov 16, 2008 at 1:32 PM, Maurício [EMAIL PROTECTED] wrote:
Hi,
Why is this wrong?
class MyClass r where function :: r - s
data MyData u = MyData u
instance MyClass (MyData v) where function (MyData a) = a
GHC says that the type of the result of 'function' is both
I've had the same experience with runghc in GHC 6.10.1 on Vista.
/g
2008/11/12 Lyle Kopnicky [EMAIL PROTECTED]:
Hi folks,
I'm using System.IO.getLine to read input in my program. I've compiled it on
Windows Vista with ghc-6.10.1. I've noticed that if I press Ctrl+C while the
program is
On Tue, Oct 28, 2008 at 12:31 PM, Andrew Coppin
[EMAIL PROTECTED] wrote:
This isn't specifically to do with Haskell, but... does anybody have any
idea roughly how fast various CPU operations are?
Yes: it's architecture dependent. I imagine you'll need to make your
questions at least somewhat
On Thu, Oct 23, 2008 at 11:00 AM, Andrew Coppin
[EMAIL PROTECTED] wrote:
I was under the impression that this is impossible, so I'm now slightly
worried.
I'm not sure why you'd think that:
import Foreign
fail :: IO Int
fail = peek nullPtr
main = fail = print
/g
--
I am in here
mapM and mapM_ have different complexity - I don't know if the
compiler would be smart enough to infer mapM_ style behavior for (void
. mapM).
/g
On Tue, Oct 14, 2008 at 10:52 AM, Mauricio [EMAIL PROTECTED] wrote:
Hi,
Wouldn't it be nice if we had something
like 'void' in
On Mon, Oct 13, 2008 at 12:29 AM, Ryan Ingram [EMAIL PROTECTED] wrote:
Of course, the point of this message isn't just to complain. The
overlap implementation was abhorrent and it *is* better now than it
was before.
I'm curious what you find abhorrent about the overlap implementation
that was
On Sun, Oct 12, 2008 at 2:12 PM, Don Stewart [EMAIL PROTECTED] wrote:
Though I note mtl doesn't actually list OverlappingInstances in its
.cabal file,
Indeed - MTL seems to have been rewritten at some point in the past to
prefer exhaustive enumeration to overlap.
Thank you for the other
As long as you don't mind producing two-color images,
http://haskell.org/haskellwiki/Library/PNG is an option. I found it
very easy to extend it to eight-bit grayscale - I didn't need
fullcolor images.
/g
On Sat, May 3, 2008 at 11:12 PM, Nahuel Rullo [EMAIL PROTECTED] wrote:
Hi list, i am new
I imagine you can get in touch with him through Epic
(www.epicgames.com) if you can't find another way to contact him.
/g
On Jan 9, 2008 4:21 PM, Galchin Vasili [EMAIL PROTECTED] wrote:
Hello,
I have been reading with great interested Tim Sweeney's slides on the
Next Generation
On Nov 21, 2007 5:16 AM, Jeremy O'Donoghue [EMAIL PROTECTED] wrote:
Not just Windows Vista. Applications and DLLs compiled with Visual
Studio 2005 (Express or full version) seem to need it to run on XP as
well.
I believe the dependency here is version 8 of the Visual C RTL.
Applications that
http://msdn2.microsoft.com/en-us/library/1w45z383(vs.71).aspx
I believe.
/g
On Nov 15, 2007 12:56 PM, Andrew Coppin [EMAIL PROTECTED] wrote:
I notice that in GHC 6.8.1, if I compile a runnably program, as well as
generating foo.exe, GHC now also generates a file foo.exe.manifest,
which
Hello,
I have code which seems to contain a memory leak, but I'm not sure
where it is or what's causing it. Any help would be greatly
appreciated:
The code is:
data Ratings = Ratings { movieCount :: Int
, movieLookup :: IOUArray Int Word32
,
I believe that rnf from the Control.Parallel.Strategies library
shipped with GHC 6.6.1 is equivalent to deepSeq, as in:
x `deepSeq` yis equivalent to rnf x `seq` y
Isn't it?
/g
On 9/12/07, Peter Verswyvelen [EMAIL PROTECTED] wrote:
Thanks for all the info.
It's really good news that
This is probably just me, but I've always mentally separated the list
monad (representing choice) from operations on ordered sets
implemented by lists (which don't always have to represent choice).
In this case, since the remainder of the code wasn't monadic, I find
it much easier to understand
On 7/18/07, Dougal Stanton [EMAIL PROTECTED] wrote:
I worked out that [ (a,b) | a - as, b - bs ] must be equivalent to
comp = concatMap (\x - map ((,) x) ys) xs
but I can't really say how conditions like a /= b get slotted in to
that style. Is there a reference for that?
As I understand it,
Hi James.
I would be tempted to write this a little differently than you did.
First, some of the pieces you've written have equivalents in the
standard library; there's no harm in rewriting them, but I figured I'd
point out that they're there. (Hoogle - haskell.org/hoogle, I believe
- can be a
On 7/17/07, Anthony Clayden [EMAIL PROTECTED] wrote:
2. The inits . tails approach adds a fault:
It introduces a sprinkling of empty sub-sequences. These
have sum zero.
So in case the input list is all negative numbers ...
At least the concatMap inits . tails code that I posted also
morph :: ([a] - Maybe (b,[a])) - (b - [a]) - [a] - [a]
Any reason not to call it 'replace'?
/g
On 7/6/07, Jules Bean [EMAIL PROTECTED] wrote:
Hi,
Yet another Function looking for a name post. Here's the type:
morph :: ([a] - Maybe (b,[a])) - (b - [a]) - [a] - [a]
Here, I am calling
Microsoft's Component Object Model.
http://en.wikipedia.org/wiki/Component_Object_Model
/g
On 6/27/07, Andrew Coppin [EMAIL PROTECTED] wrote:
Simon Peyton-Jones wrote:
The biggest Haskell/COM project I know of was Krasimir's
implementation of Visual Haskell, which was a plug-in for Visual
More generally, that's unfoldr:
Prelude :t Data.List.unfoldr
Data.List.unfoldr :: (b - Maybe (a, b)) - b - [a]
unfoldr represents the end of the unfold explicitly (using Nothing)
instead of implicitly (using the empty list).
/g
On 27 Jun 2007 20:26:56 +0100, Jon Fairbairn [EMAIL PROTECTED]
On 6/8/07, Bulat Ziganshin [EMAIL PROTECTED] wrote:
I second that. I particularly like the elimination of ]'s. We certainly
need some symbol to separate the map and the key; but we do really need
to also mark here be the end of the key?
and how (arr ! key ++ data) should be parsed? :)
On 2/6/07, Yitzchak Gale [EMAIL PROTECTED] wrote:
J. Garrett Morris wrote:
Well, no, but it is at least no worse than
apply :: Handle - Attribute a -
ContT (StateT Blargh (ErrorT Fzzt IO)) a
I find that in general, many functions do
not need all of the capabilities. If they do,
you can alias
On 2/5/07, Yitzchak Gale [EMAIL PROTECTED] wrote:
J. Garrett Morris wrote:
First, we'll create a transformed version of the IO monad,
Why go to the trouble of creating a new monad?
The existing ones are fine.
Mainly to keep the type error messages simpler. A project I was
working on started
On 2/5/07, Yitzchak Gale [EMAIL PROTECTED] wrote:
J. Garrett Morris wrote:
Mainly to keep the type error messages simpler.
There are two ways to get around that problem:
1. Make your functions polymorphic, using
MonadState, MonadError, etc. Each function
mentions only the capabilities
Maybe has a Monad instance, so you can write this as follows (untested):
exists str wmap = boolFromMaybe exists'
where exists' =
do x - Map.lookup (sort str) wmap
find (== str) (snd x)
boolFromMaybe (Just _) = True
boolFromMaybe Nothing = False
On 2/4/07, Udo Stenzel [EMAIL PROTECTED] wrote:
J. Garrett Morris wrote:
Small improvement (Data.Maybe is underappreciated):
exists str wmap = isJust exists'
where exists' =
do x - Map.lookup (sort str) wmap
find (== str) (snd x)
This is true. Some time
On 2/4/07, Udo Stenzel [EMAIL PROTECTED] wrote:
J. Garrett Morris wrote:
On 2/4/07, Udo Stenzel [EMAIL PROTECTED] wrote:
Well, depends on whether we are allowed to define new combinators. I
sometimes use
-- Kleisli composition
infixl 1 @@
(@@) :: Monad m = (a - m b) - (b - m c) - (a - m c)
f
On 2/4/07, Martin Huschenbett [EMAIL PROTECTED] wrote:
Hi,
I've often got the same pattern with nested Maybes but inside the IO
monad (sure this could be every other monad too). Assuming that I've got
functions:
This is where my favorite part of the mtl steps in: monad transformers.
First,
Uh, apologies. I got confused between reading your post and playing
for a while, and answered the wrong question.
/g
On 2/2/07, J. Garrett Morris [EMAIL PROTECTED] wrote:
On 2/2/07, Chad Scherrer [EMAIL PROTECTED] wrote:
So in reality, I'm trying to construct something like
f :: (a - STM b
On 1/31/07, Andrew Wagner [EMAIL PROTECTED] wrote:
So, a couple of questions to ponder about this: Is this unique to
Haskell, or could the same be said about any functional language? How
can we teach this better to newbies? Most of what I see in the
tutorials is Higher order functions accept
On 1/28/07, Alexy Khrabrov [EMAIL PROTECTED] wrote:
How do people stumble on Haskell?
My story isn't as interesting as some of these. My first quarter in
school, I took a course taught in Scheme. I expressed some
dissatisfaction with the lack of types (and, in particular, the
collection of
Agreed. I've written quite a bit of code that way myself. Looking at
Iavor's monadLib, though, raised a question: has there been any
consider of removing the requirement that the newtype be the last
argument? The classes for state monads, etc. are rather backwards as
it is, since the
fmap. e.g.:
Prelude fmap ('c':) (Just a)
Just ca
Prelude fmap ('c':) Nothing
Nothing
Prelude
/g
On 1/25/07, John Ky [EMAIL PROTECTED] wrote:
Is there a built-in function that already does this?
foo :: (a - b) - Maybe a - Maybe b
foo f m
| isNothing m = Nothing
| otherwise = Just (f
On 1/4/07, brad clawsie [EMAIL PROTECTED] wrote:
lets say i have a string
s = abcdefg
now i have two lists of strings, one a list of patterns to match, and
a list of replacement strings:
patterns = [a,b]
replace = [Z,Y]
from which my intent is that a be replaced by Z, b by Y etc
now using
Oops, I seem not to have proofread my message.
On 1/4/07, J. Garrett Morris [EMAIL PROTECTED] wrote:
On 1/4/07, brad clawsie [EMAIL PROTECTED] wrote:
s = abcdefg
patterns = [a,b]
replacements = [Z,Y]
I changed the name here so as not to conflict with the replace function.
snip
You can
On 12/22/06, Reto Kramer [EMAIL PROTECTED] wrote:
What I'm really looking for is not so much the chaining of StateT
compositions, but rather the isolation of StateA from StateB while
they both flow from the search loop into the respective library calls
(foo, bar) transparently to the application
Hello everyone,
I recently found myself attempting to use ST at the base of a stack of
transformers, ala:
type Test t r = ErrorT String (ST t) r
I imagined, given the type of ST, that I would need a run function
along the lines of:
runTest :: (forall t. Test t r) - Either String r
(which
Hmm, that was simpler than I had imagined. Thank you both!
/g
On 12/22/06, Stefan O'Rear [EMAIL PROTECTED] wrote:
On Fri, Dec 22, 2006 at 06:44:54PM +0100, Pepe Iborra wrote:
Rank-2 types seem to interact badly with (.) and ($), but my type
theory educated neuron doesn't know why. I think
On 12/20/06, Diego Navarro [EMAIL PROTECTED] wrote:
take map for example, and fmap, I don't think they
should be named different (fmap is ugly, not
suggestive, and conceptually the same).
mplus could be renamed (++) (they are conceptually the
same
Wouldn't this raise the same problems
On 12/13/06, Donald Bruce Stewart [EMAIL PROTECTED] wrote:
* Give tips on how to answer questions
+ Ok. we can put up an article here. Some suggestions:
- Solutions with unsafePerformIO should be discouraged (moreso
;)
I'd like to at least suggest a slight
Hello everyone,
On 12/12/06, Ketil Malde [EMAIL PROTECTED] wrote:
snip
Some things took a bit of effort to wrap my head
around, but it generally wasn't too hard to get to a level where I could
write useful programs.
snip
* I'm already productive with what I know, so I don't have the direct
On 12/11/06, Mark T.B. Carroll [EMAIL PROTECTED] wrote:
I'm not sure I actually understand them properly yet, but I'm already
curious about if anybody's played with them in Haskell, or how useful
it would be to do so. Any comments?
Haskell implementations of the transformers in Espinosa's
On 12/8/06, Kurt Schelfthout [EMAIL PROTECTED] wrote:
Hi Haskell'ers,
snip
class Activity a c where
start :: c - a - Time --start of the activity (this isn't
actually dependent on c, I guess)
end :: c - a - Time --end of the activity
delta :: a - Time - c
On 12/7/06, Cat Dancer [EMAIL PROTECTED] wrote:
On 12/7/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote:
I'm sure from a single example I could understand what was going on
and elaborate from there.
Let's say I want to get a line from the user, and either return an
integer or an error string
I generally use the Typeable class for this. In that example, you'd want:
class Typeable a = Shape_ a
instead of just
class Shape_ a
and then your filter predicate would look like:
isSquare :: Shape - Bool
isSquare (Shape s) = typeOf s == typeOf square
where square :: Square ; square =
Hello,
First, and forgive me if I'm making unwarranted assumptions, but
http://haskell.org/haskellwiki/Homework_help might be useful.
Second: div, mod, reverse, and the unfoldr function from Data.List
will do what you want.
/g
On 11/25/06, escafia [EMAIL PROTECTED] wrote:
Hi,
i've one
On 11/17/06, Henning Thielemann [EMAIL PROTECTED] wrote:
On Fri, 17 Nov 2006, Clara Zamolo wrote:
buildCouples = snd . foldl op (0,[])
where
op (v,xs) x = (v+x,xs++[(x,v)])
You could make something like this that doesn't have quadratic-type
appends by accumulating functions
On 10/14/06, Nicolas Frisby [EMAIL PROTECTED] wrote:
Perhaps the editor could assume a default precedence when the
user-defined precedence is not yet available. Preferably, the editor
would also somehow yell at the user to indicate that it is making such
an assumption.
Perhaps it could even
On 10/3/06, Edward Ing [EMAIL PROTECTED] wrote:
The source is below. Side is types as Float. My assumption was that
Haskell would know how to convert the Int to a float and all would be
well. I am I mistaken somewhere? The problem is with the last line.
Yes - Haskell does not automatically
I've always used:
roundn n f = fromIntegral (round (f * 10 ^ n)) / 10 ^ n
I may have missed some bugs or subtleties of floating point numbers, though.
/g
On 9/8/06, Sara Kenedy [EMAIL PROTECTED] wrote:
Hello all,
I try to find some functions in Haskell library to deal with numeric
such that
The ghc flag -fwarn-incomplete-patterns might be what you're looking for.
/g
On 8/8/06, Jens Theisen [EMAIL PROTECTED] wrote:
Hello,
as a haskell newbie I'm wondering about the following question.
Are there options to popular haskell implementations or other means
(haskell lint?) to check
On 8/1/06, Stephane Bortzmeyer [EMAIL PROTECTED] wrote:
How to do it in Haskell? How can I call functions like Prelude.head
while being sure my program won't stop, even if I call head on an
empty list (thus calling error)?
Try looking at Control.Exception. For example:
module Test where
main n = putStrLn (replicate n '*')
main n = putStrLn (take n (repeat '*'))
main n = sequence (take n (repeat (putStr *)))
(but that doesn't have a final new line. The more complicated:
main n = sequence (take (n - 1) (repeat (putStr *))) putStrLn *
should solve that problem.)
/g
On
Off the top of my head:
separate :: String - [String]
separate [] = []
separate s =
case break (',' ==) s of
(s,[]) - [s]
(s,',':s') - s : separate s'
_ - error how did we get here?
There is at least one cunning rewriting with foldl, I think, but I
think this version is clearer.
/g
On 6/9/06, Brandon Moore [EMAIL PROTECTED] wrote:
data DataType m = forall m' . (Monad m') = DataType (TyEq m m') (Char
- m' ())
It appears that the more intuitive formulation:
data DataType m
where DataType :: Monad m = (Char - m ()) - DataType m
should work in GHC 6.4
/g
Data.List contains
sort :: Ord a = [a] - [a]
and
sortBy :: (a - a - Ordering) - [a] - [a]
I believe they're currently implemented using merge sort, at least in GHC.
/g
On 2/16/06, Radu Grigore [EMAIL PROTECTED] wrote:
Is there a sort function in the libraries that come with GHC (6.4)? My
I think the function you're looking for is:
myRound n places = round (n / fromIntegral factor) * factor
where factor = 10 ^ (places - 1)
In this case, 10 ^ (places - 1) has integral type (either Int or
Integer). I need it to be a fractional type to divide n by it, so I
use fromIntegral to
tootieIndices = findIndices isTootie
where isTootie (Pa _) = False
isTootie (Tootie _) = True
would be my first approach.
/g
On 2/10/06, Creighton Hogg [EMAIL PROTECTED] wrote:
Hi,
If I have something like
data Patootie = Pa Int | Tootie Int
and I want to pull out the
On 2/4/06, raptor [EMAIL PROTECTED] wrote:
does Haskell have a property lists. Like Lisp ?
any pointer to examples ?
Not built in to the language. It's not hard to get the same
functionality though - I've attached a module that takes a (not
tremendously elegant) approach to the same thing,
On 12/22/05, Daniel Carrera [EMAIL PROTECTED] wrote:
Hi all,
How do I write a statement that spans multiple lines?
I have this function:
pythagoras n = [(a,b,c) | a -[1..n], b -[1..n], c -[1..n], a = b, b
c, a*a + b*b == c*c]
This should all be in one line. I know some ways to make the
In ghci at least, you can enter definitions like that using let binding:
let mysquare x = x * x
/g
On 12/22/05, Greg Woodhouse [EMAIL PROTECTED] wrote:
In neither GHCi nor Hugs (so far as I know) is it possible to
interactively enter definitions. coming from Scheme, this was a bit of
a
On 12/8/05, Robin Green [EMAIL PROTECTED] wrote:
Sure, I take your point. But I just jumped on my latest hobby-horse: verbosity
of imperative code is not that necessary.
There was a discussion along these lines some time ago, started by
Frederik Eaton with the subject line Mixing monadic and
On 10/21/05, Joel Reymont [EMAIL PROTECTED] wrote:
On Oct 21, 2005, at 4:22 PM, Stefan Monnier wrote:
You mean you'd like
data TableInfo = TableInfo {
avgPot :: Double,
No, I would actually like to offset avgPot 4 spaces from TableInfo.
Can I throw a vote
the similar function:
mapM :: Monad m = (a - m b) - [a] - m [b]
should do the trick for you, and is in the prelude.
/g
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On 9/20/05, Karl Grapone [EMAIL PROTECTED] wrote:
What I want to be able to do is add and remove fields while the system
is running, I suppose via hs-plugins, and I should be prevented from,
for example, accidentally taking an employees first name and using it
as a departments address.
I know
--- Ketil Malde wrote:
Or, what if String were one? Could we have painless read/show with
arrays of Char, as well as lists, for instance?
--- end of quote ---
I think with a decent set of type classes for collections, better handling of strings
would come for free. If any list function could
--- Malcolm Wallace wrote:
As an example, instead of the following list-only code,
f :: List a - ...
f []= ...
f (h:t) = ...
you could write this more general version, which assumes only some
class Sequence with operations null, head, tail, etc.
f :: Sequence s = s a - ...
--- Tom Pledger wrote:
It could get more convenient, though, if we have data-constructors-as-class-members
and move the familiar list constructors into the List class. (The following might need
to be built into the compiler, because of the special [] syntax.)
--- end of quote ---
Changing the
--- John Goerzen wrote:
tick :: Int - State Int Int
tick newval = do put newval
return newval
Or this:
tick :: State Int Int
tick = do n - get
return n
That is even more incomprehensible to me -- why would removing a line
before the return cause a type error?
--- end
--- [EMAIL PROTECTED] wrote:
I wish I knew what that meant. If someone could explain it and tell me
what's wrong, I'd appreciate it.
--- end of quote ---
Lexeme is actually a selector function over the TokenParser record. In the previous
section (also on lexical analysis), he included the
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