With cabal-install, usually.
Limestraël wrote:
Cabal/cabal-install are good tools for distribution and installation,
but I was wondering -- as I was starting to learn how to use Cabal --
how do usually Haskell developpers build their softwares (and especially
medium or big libraries) while the
For the reference: foldM is defined as
foldM :: Monad m => (a -> b -> m a) -> a -> [b] -> ma
foldM _ a [] = return a
foldM f a (x:xs) = f a x >>= \fax -> foldM f fax xs
Let's define
foldM' f x xs = lazy'foldl f (Just x) xs
We can check that foldM' satisfies the same equations as foldM:
foldM'
The problem is, "fromSql x" doesn't know that type it should return. It's sure that it
has to be of class "Convertible SqlValue", but nothing more. Could be String, or Int32,
or something else.
What if you just omit the "show" function? fromSql seems to be able to convert
almost anything to St
-- {-# LANGUAGE FunctionalDependencies#-}
-- {-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}
module Register where
-- class Register a r | a -> r
class Register a where
type R a
-- instance Register Int Int
instance Register Int where
type R Int = Int
-- instance Regis
I'd say we don't really need subclasses. I mean, what's the difference:
class Eq a where (==) :: a -> a -> Bool
instance Eq a => Eq (Maybe a) where
Nothing == Nothing = True
Just x == Just y = x == y
_ == _ = False
sort :: Eq a => [a] -> [a]
or
data Eq a = Eq {eq :: a -> a -> Bool}
eqMayb
s/subclasses/classes/
Sorry for the confusion.
Miguel Mitrofanov wrote:
I'd say we don't really need subclasses. I mean, what's the difference:
class Eq a where (==) :: a -> a -> Bool
instance Eq a => Eq (Maybe a) where
Nothing == Nothing = True
Just x == Just y =
Sorry, no luck with that.
But you can, probably, define some "customized comma":
data DrawPair a b = DrawPair a b
(<,>) :: a -> b -> DrawPair a b
(<,>) = DrawPair
instance (Drawable a, Drawable b) => Drawable (DrawPair a b) where ...
drawMany :: Drawable a => Window -> a -> IO ()
...
drawMany wi
Which "a" should it use for "methods"?
On 4 Mar 2010, at 09:07, muneson wrote:
When writing a command-line interface I ran into type class conflicts
I don't understand. Could anyone explain why ghc 6.10.4 compiles this
methods :: (Eq a) => [(String, a)]
methods =
[ ("method1", undefined )
MigMit:~ MigMit$ cabal --help
This program is the command line interface to the Haskell Cabal
infrastructure.
See http://www.haskell.org/cabal/ for more information.
^
|
+
On 8 Mar 2010, at 19:51, Andrew Coppin wrote:
OK, so apparent
Maybe it's just me, but I think composition chain is MUCH easier to read.
When readning, I'd probably transform the last version to the previous one by
hand, just to make it more comprehensible.
Sebastian Fischer wrote:
On Mar 10, 2010, at 8:47 AM, Ketil Malde wrote:
I think it is better st
1) Haven't look closely, but your second ArrowLoop instance seems righter. The
question really is the same as with MonadFix instances; you can always define
an instance like this
data M = ... -- whatever
instance Monad M where ...
instance MonadFix M where mfix f = mfix f >>= f
...but this gen
Out of curiosity: is there something wrong with my nickname "migmit"?
I'm not gonna change it anyway.
On 6 Apr 2010, at 09:52, Edward Z. Yang wrote:
This is a pretty terrible reason, but I'm going to throw it out there:
I like real names because they're much more aesthetically pleasing.
In
Doesn't seem right. IMHO, the necessity of making windows NOT fullscreen is an
indication of bad design.
Thomas Davie wrote:
On 7 Apr 2010, at 02:53, Ben Millwood wrote:
On Wed, Apr 7, 2010 at 2:22 AM, Thomas Schilling
wrote:
I have
set a maximum width on purpose so that it doesn't degrade
Well, what's the sum of an empty list? Seems naturally that it's 0, but why?
Let's say that sum [] = x.
If we take two lists, say, l1 = [1,2,3] and l2 = [4,5], then
sum l1 + sum l2 = 6 + 9 = 15 = sum [1,2,3,4,5] = sum (l1 ++ l2)
We expect it to be the case even if one of the lists is empty, so
Forgot about this one:
Bjorn Buckwalter wrote:
What got me thinking about this was the apparently incorrect intuition
that 'and xs' would imply 'or xs'.
No. See, "and" is very close to "for all", and "or" is similarly close to "exists". For example, the statement "all crows are black" means j
It's called "monad transformers"
func1' :: Int -> EitherT Error IO String
func1' n = EitherT $ func1 n
func2' :: Int -> EitherT Error IO String
func2' s = EitherT $ func2 n
runCalc' :: Int -> EitherT Error IO [String]
runCalc' param = func1' param >>= func2'
runCalc :: Int -> IO (Either Error [St
ErrorT :: IO (Either Error String) -> ErrorT Error IO String
I can think that can be written as
ErrorT :: IO (Either Error String) -> ErrorT Error (IO String)
Am I correct?
No, you're not. Similar to function application, type application is
also left-associative, so it can (but shouldn't)
(>>= f) is equivalent to (flip (>>=) f), not to ((>>=) f). You can try this
with your own function this way:
(&$^) :: (Monad m) => m a -> (a -> m b) -> m b
(&$^) = undefined
:t (&$^ f)
Milind Patil wrote:
For a function
f :: a -> m b
f = undefined
I am having trouble understanding how the
On 19 May 2010, at 08:35, Ivan Miljenovic wrote:
This looks suspiciously like homework...
2010/5/19 R J :
What are some simple functions that would naturally have the
following type
signatures:
f :: (Integer -> Integer) -> Integer
I can only think of one solution to this but it doesn't gu
That won't be a great idea; if I just want my monad to be declared as one, I
would have to write
instance Functor MyMonad where fmap = ...
instance Pointed MyMonad where pure = ...
instance Applicative MyMonad where (<*>) = ...
instance Monad MyMonad where join = ...
Compare this with
instance
From Prelude.hs:
class (Eq a) => Ord a where
compare :: a -> a -> Ordering
(<), (<=), (>), (>=) :: a -> a -> Bool
max, min :: a -> a -> a
compare x y = if x == y then EQ
-- NB: must be '<=' not '<' to validate the
--
listFs = [f1, f2, f3]
map ($ x) listFs -- same as [f1 x, f2 x, f3 x]
f x y z = ...
map (\x -> f x u v) xs
On 17 Jun 2010, at 23:02, Martin Drautzburg wrote:
Hello all
The standard map function applies a single function to a list of
arguments.
But what if I want to apply a list of functions
I disagree. First of all, UHC states explicitly that some features are not supported (and probably never would be). Secondly, it seems like
almost nobody uses (n+k)-patterns, and when they are used, they make the code less readable; so it's good NOT to support them, in order to make
programmers a
Well, the problem is that every implementor does choose a subset of standart to
implement.
It's much worse in JavaScript - essential features working differently in Internet Explorer, Firefox, Opera, and Safari, and sometimes they even
differ between versions; Web programmers still manage. (n+k
l to be equally bad.
On Mon, Apr 20, 2009 at 1:23 PM, Miguel Mitrofanov
wrote:
Well, the problem is that every implementor does choose a subset of standart
to implement.
It's much worse in JavaScript - essential features working differently in
Internet Explorer, Firefox, Opera, and Safari, and
On 21 Apr 2009, at 04:59, Richard O'Keefe wrote:
On 20 Apr 2009, at 10:12 pm, Miguel Mitrofanov wrote:
I disagree. First of all, UHC states explicitly that some features
are not supported (and probably never would be). Secondly, it seems
like almost nobody uses (n+k)-patterns,
Ho
$ cat .cabal/config
...
root-cmd: sudo
...
user-install: False
...
On 21 Apr 2009, at 14:41, Achim Schneider wrote:
Thomas Davie wrote:
There seems to be an assumption amongst the community that a user's
home directory is the most useful place for cabal to install to by
default. A few peopl
On 22 Apr 2009, at 13:07, Jon Fairbairn wrote:
Miguel Mitrofanov writes:
Well, the problem is that every implementor does choose a
subset of standart to implement.
That's what I'm complaining about.
And that's exactly what you (or anybody else) can't do anything ab
On 22 Apr 2009, at 21:19, Jason Dusek wrote:
2009/04/22 Miguel Mitrofanov :
It's arrogant and disrespectful on the part of the
implementors to say that they know better than the committee
what features should be part of the language.
It's arrogant and disrespectful on the p
On 23 Apr 2009, at 12:17, Thomas Davie wrote:
On 23 Apr 2009, at 10:02, Matthijs Kooijman wrote:
Some material I've read on typography -- can't find the
reference now -- suggests ~65 is the best number of characters
per line. The advice was, if your page is larger than that,
you should make
On 23 Apr 2009, at 23:07, Claus Reinke wrote:
*Main> :t rollDie ~>> (rollDie ~>> rollDie)
rollDie ~>> (rollDie ~>> rollDie) :: Seed -> (Int, Seed)
This is a function. How exactly do you want ghci to show it? When
you figure that out, feel free to make an instance of Show for it.
Just becaus
Have you considered using FFI?
On 24 Apr 2009, at 20:36, Sam Martin wrote:
Hi Everyone,
It appears the GHC compiler (and other) compile Haskell *via-C* but
not
*to C*. I've never really understood why there isn't a C generation
option, or why GDC ships with its own compulsory copy of gcc.
ys "derive everything possible". Therefore, it seems
pointless to move it to another line.
On 24 Apr 2009, at 16:37, Loup Vaillant wrote:
2009/4/23 Miguel Mitrofanov :
On 23 Apr 2009, at 12:17, Thomas Davie wrote:
Haskell is a very horizontal language, and to limit our horizontal
On 25 Apr 2009, at 17:32, j.waldmann wrote:
* with practically every modern IDE
You mean, with Emacs?
* indentation should be by fixed amounts (e.g. 4 spaces for each
level)
and not depend on lengths of identifiers (because you might later
change
them)
Agreed. I always write code tha
On 25 Apr 2009, at 18:34, Xiao-Yong Jin wrote:
Miguel Mitrofanov writes:
On 24 Apr 2009, at 16:37, Loup Vaillant wrote:
2009/4/23 Miguel Mitrofanov :
On 23 Apr 2009, at 12:17, Thomas Davie wrote:
Haskell is a very horizontal language, and to limit our horizontal
space
seems pretty
On 25 Apr 2009, at 19:08, Felipe Lessa wrote:
On Sat, Apr 25, 2009 at 10:34:05AM -0400, Xiao-Yong Jin wrote:
You don't write lisp, do you? Or probably it is just me.
But I would prefer to write the line as
newtype MyCoolMonad = MyCoolMonad (FirstTransformer
On 25 Apr 2009, at 19:59, Felipe Lessa wrote:
On Sat, Apr 25, 2009 at 07:38:59PM +0400, Miguel Mitrofanov wrote:
Also, I don't mistake the transformers as different
parameters because of the parenthesis
You should really try Lisp. In my opinion, parenthesis are a kind of
noise - too
On 25 Apr 2009, at 21:53, Jason Dusek wrote:
Many Haskell/JS bridges provide libraries for writing complete
JavaScript programs in Haskell; some of them even include
jQuery. However, my goals are more limited -- I'd like to be
able to take a Haskell module and turn it into a JavaScript
obj
{-# LANGUAGE MultiParamTypeClasses #-}
class Returnable m a where ret :: a -> m a
class Bindable m a b where bind :: m a -> (a -> m b) -> m b
newtype MOAMonad r m a = MOAMonad ((a -> m r) -> m r)
instance Monad (MOAMonad r m) where
return x = MOAMonad $ ($ x)
MOAMonad h >>= f = MOAMonad $
Short answer: that's impossible.
Well, with some oleging it should be possible, but the very fact that
you're trying to do something like this indicates that you're doing
something wrong. Where did this list of parameters came from? May be,
you can apply your function to them one at a time,
On 6 May 2009, at 19:27, Adrian Neumann wrote:
Hello,
I'm trying to prove the unfold fusion law, as given in the chapter
"Origami Programming" in "The Fun of Programming". unfold is defined
like this:
unfold p f g b = if p b then [] else (f b):unfold p f g (g b)
And the law states:
unf
Anyway, I can't see why we still use mailing lists when we have
reddit, which
has all the good parts of mailing lists (nested messages), while it
also:
Hmm, what's this reddit thing? *googles*
Me too. Seems like this "reddit" thing is nothing but a mail list done
wrong. I may be wrong, but
* in the Appendix on notation, he defines composition of functions
the "wrong way around" (i.e., the Haskell way, (f.g)(x) = f(g(x)).
Just to make sure I understand correctly: are you claiming that Haskell
definition of composition is wrong?
___
Has
I have a suggestion.
Why don't you grab some introductory book on Haskell and learn Haskell syntax a
little?
applebiz89 wrote on 07.05.2009 13:46:
I havent done much IO at all in haskell, only within the function itself.
However I want to get the input from the interface for the function and
h
I have a question regarding the connection between monads and comonads.
I always thought of the comonad operations as being the inverse
operations of the corresponding monad functions.
That's not true.
If this is the case I would like to know what the corresponding monad
for the following com
Seems like I was wrong. It does satisfy comonad laws. Sorry.
However, the "duality" of monads and comonads isn't that simple. A comonad is actually a monad itself, but in different category. It has nothing
to do with inverse functions etc.
Jan Christiansen wrote on 08.05.2009 14:47:
Hi,
I ha
j.waldmann wrote on 08.05.2009 17:39:
Wow. This is really a bikeshed discussion. My post contained praise for the
book,
a critique of one of its design decisions (intermediate language not
explicitely typed),
and a syntactical remark. Guess what the discussion is about.
(This is also known as
Types.
(>>=) :: Monad m => m a -> (a -> m b) -> m b
(1+) :: Num a => a -> a
So, the typechecker deduces that 1) "a" is the same as "m b", and 2)
"a" (and "m b", therefore) must be of class "Num"
Now,
Just 3 :: Num t => Maybe t
and the typechecker learns from that that "m a" must be the sa
On 10 May 2009, at 00:30, Brandon S. Allbery KF8NH wrote:
On May 9, 2009, at 15:31 , michael rice wrote:
Prelude> Just 3 >>= (1+)
That (a -> m b) in the middle is what's failing to typecheck. The
error is a bit obtuse because ghci is trying hard to find a way to
do what you want, so it
On 10 May 2009, at 04:00, Cory Knapp wrote:
... There have been 12 replies to this question, all of which say
the same thing.
Brandon's one was different. And incorrect, which shows that this
question isn't completely obvious.
I'm glad we're so happy to help, but does
Just 3 >>= return
On 10 May 2009, at 09:24, Brandon S. Allbery KF8NH wrote:
I can't tell where I'm making the mistake here.
Frankly, I can't do it either, because I don't understand what you're
talking about.
It seems that you have some idea of how the typechecker works, which
is very different from that
I think that it's not nice to export 200 declarations from a single
module.
On 12 May 2009, at 18:05, Maurício wrote:
Hi,
When we want to list which declarations are exported by a module
we do:
module Mod ( list of exports ) where ...
Are there propositions to alternatives to that (I could
Neil Brown wrote on 13.05.2009 14:23:
Leaving aside the arguments about
200 exports, even for 20 exports it would sometimes be cleaner to write
the above to hide one, than to spell out the other 19 in an export list.
Note that Haddock orders exports according to the export list, not to an or
What would you expect
foo [id, \x -> x]
to be?
Martin Hofmann wrote on 15.05.2009 12:09:
It is pretty clear, that the following is not a valid Haskell pattern:
foo (x:x:xs) = x:xs
My questions is _why_ this is not allowed. IMHO, the semantics should be
clear: The pattern is expected to succe
Conor McBride wrote on 15.05.2009 16:19:
My guess is that if this feature were already in, few would be campaigning to
remove it.
You're probably right. For example, I'm not compaigning to remove multiple inheritance (from non-abstract classes) from C++. But I still think
it's an ugly feat
On 18 May 2009, at 20:29, Joe Fredette wrote:
While an incredibly small font is a clever option, a more serious
suggestion may be as follows.
3-4 slides imply 3-4 topics, so the question is what are the 3-4
biggest topics in haskell? I would think they would be:
* Purity/Referential Tran
On 19 May 2009, at 09:06, Ryan Ingram wrote:
This is a common problem with trying to use do-notation; there are
some cases where you can't make the object an instance of Monad. The
same problem holds for Data.Set; you'd can write
setBind :: Ord b => Set a -> (a -> Set b) -> Set b
setBind m f
gt; C m r a
and backwards.
Jason Dusek wrote on 19.05.2009 10:23:
2009/05/18 Miguel Mitrofanov :
On 19 May 2009, at 09:06, Ryan Ingram wrote:
This is a common problem with trying to use do-notation; there are
some cases where you can't make the object an instance of Monad. The
same problem holds
michael rice wrote on 19.05.2009 18:16:
Cool!
Is there *anything* Haskell *can't* do?
Well, I haven't found a way to emulate polymorphics kinds yet, and I feel like
I need them. Other than than - probably no.
Michael
--- On *Mon, 5/18/09, David Menendez //* wrote:
From: David Men
On 24 May 2009, at 01:19, Max Cantor wrote:
Going through the instances for HTypeable (http://www.haskell.org/HaXml/HaXml/src/Text/XML/HaXml/TypeMapping.html#toHType
) I saw the following instance for Either a b.
My question is, why doesn't the pattern match in the where clause
always fail?
And I would certainly celebrate when "if b then x else y" expression becomes polymorphic
in "b".
Edsko de Vries wrote on 27.05.2009 17:33:
+1. I agree completely, I've missed this often for exactly the same
reasons.
Edsko
___
Haskell-Cafe mailing l
On 27 May 2009, at 23:38, Simon Peyton-Jones wrote:
Folks
Quite a few people have asked for splices in Template Haskell
*types*, and I have finally gotten around to implementing them. So
now you can write things like
instance Binary $(blah blah) where ...
or f :: $(wubble bu
It's trying to 'Show' the 'c [Int]' type, but doesn't know which 'c'
to use; so it's trying to find a generic instance, which doesn't
exist. You can't fix this with 'deriving' or anything like this;
instead, provide the type annotation like this:
*Main> searchAll g 1 3 :: Maybe [Int]
On 31
data Container a = Container a [a] ?
Or, maybe, you need something like zipper.
On 5 Jun 2009, at 01:53, Günther Schmidt wrote:
Hi,
I need to design a container data structure that by design cannot be
empty and can hold n elements. Something like a non-empty list.
I started with:
data
Do you really need a class? Maybe, a simple data type would do?
So, instead of
class MyMonad m where
myVal1 :: m a
myVal2 :: m a -> m [a]
instance Monad m => MyMonad (MyMonadT m) where
myVal1 = foo
myVal2 = bar
you can write (in your first package) something like
data MyMonad m
Miguel Mitrofanov wrote on 05.06.2009 16:53:
myMonadT :: Monad m => MyMonad m
Sorry, I've meant
myMonadT :: Monad m => MyMonad (MyMonadT m)
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Probably because you don't apply "x" to "xx" anywhere?
On 6 Jun 2009, at 11:48, John Ky wrote:
Hi Haskell Cafe,
In the following code, I get an error saying Ambiguous occurrence
`x'. Why can't Haskell work out which x to call based on the type
of getA?
Thanks
-John
#!/usr/bin/env runh
"r <- randomRIO (1,10)" is NOT the source of error. Why do you think it is?
ptrash wrote on 10.06.2009 15:55:
Hi,
I have tried on the console to write
x <- randomRIO(1,10)
:t x
Everythings fine and the type of x is
x :: Integer
Now I have tried to write a Method which gives me a Number of r
I recently discovered an interesting way of closing typeclasses while
playing with type-level peano naturals:
class Nat n where
caseNat :: forall r. n -> (n ~ Z => r) -> (forall p. (n ~ S p,
Nat p) => p -> r) -> r
I usually use this one:
class Nat n where
caseNat :: p Z -> (forall m. N
ghci> map reverse $ foldM (\answer list -> [x:answer | x <- list, not
$ x `elem` answer]) [] [[2,3], [1,2], [2,3,4], [1,2,3]]
[[2,1,4,3],[3,1,4,2],[3,2,4,1]]
On 14 Jun 2009, at 12:06, Fernan Bolando wrote:
Hi all
If I have a number of list
example
list1 = [2,3]
list2 = [1,2]
list3 = [2,3,4]
Again: what if somebody wants to answer to the original author privately? It's
easier to just use "Reply" for private answers and "Reply all"
for list answers.
Thomas ten Cate wrote on 15.06.2009 11:18:
> On Sun, Jun 14, 2009 at 21:23, Jochem Berndsen wrote:
>> Alberto G. Corona wrote:
>>> Once m
Hi!
Suppose I want to create a specific monad as a combination of monad transformers - something like "StateT smth1 (ReaderT smth2 Identity)". As
you can see, each transformer is parametrized with a type of kind *. I want to abstract these parameters, so that instead of "StateT smth..." I
can w
But some of us would definitely find it amusing.
Deniz Dogan wrote on 15.06.2009 16:53:
2009/6/15 minh thu :
2009/6/15 Uwe Schmidt :
Dear Haskellers,
who needs this kind of documentation?
http://hackage.haskell.org/packages/archive/tfp/0.2/doc/html/Types-Data-Num-Decimal-Literals.html
isn't
there are some more
sophisticated methods like higher-level monad - but it seems almost
impossible to abstract a class that can have an associated data type.
I don't see any reason to do this - yet; and for me, "yet" is enough
to make me nervous.
On 16 Jun 2009, at 01:25, Ashley
And the third one I forgot at first: so far, all code I wrote could be
easily ported to Hugs.
On 16 Jun 2009, at 02:00, Miguel Mitrofanov wrote:
Probably.
I have two objections against using type families. Both are pretty
much theoretical.
First, it seems to me that using type families
What do you mean, without instances? How do you call "data instance"
declarations?
On 16 Jun 2009, at 02:16, Ashley Yakeley wrote:
Miguel Mitrofanov wrote:
First, it seems to me that using type families would require some
other extensions. Multi-parameter type classes are OK,
You can use the standart "tying the knot"-technique. For example:
data Tree = TreeNode String (Maybe Tree) [Tree] -- what's the parent of the
root node?
test :: Tree
test =
let parent = TreeNode "I'm parent" Nothing [child1, child2]
child1 = TreeNode "I'm child1" (Just parent) []
On 17 Jun 2009, at 19:54, .shawn wrote:
Why does the type signature of mapTreeM look like this?
Why not? I can't think of any other possibility.
And what does it mean by "The lift tell us that we're going to be
executing a command in an enclosed monad. In this case the enclosed
monad is
Well, I'm hardly the one knowing GHC internals, but...
In allstrings you continue calling "strings" with same arguments again
and again. Don't fool yourself, it's not going to automagically
memorize what you were doing before. In fact, I'd expect much more
speed loss. If you increase your "
An answer would probably depend on the reductions order you've chosen.
Would that do?
(\e -> e (\u -> e (\v -> u))) (\f -> \x -> f x) -- all variables have
different names, see?
= (\f -> \x -> f x) (\u -> (\f -> \x -> f x) (\v -> u))
= \x -> (\u -> (\f -> \x -> f x) (\v -> u)) x
= \x -> (
Correction: I think that one can find an expression that causes name
clashes anyway, I'm just not certain that there is one that would
clash independent of whichever order you choose.
On 21 Jun 2009, at 21:12, Miguel Mitrofanov wrote:
An answer would probably depend on the reductions
Wow. Now you've showed it to me, it seems pretty obvious. That's what
I like about math.
On 21 Jun 2009, at 21:56, Bertram Felgenhauer wrote:
Miguel Mitrofanov wrote:
Correction: I think that one can find an expression that causes name
clashes anyway, I'm just not certain th
Probably the easiest way to fix this was already proposed by Deniz
Dogan: de Bruijn indices.
On 21 Jun 2009, at 21:57, Andrew Coppin wrote:
Lauri Alanko wrote:
With "name collisions" I'm assuming you mean inadvertent variable
capture. The answer depends on your evaluation strategy. If you ne
I so don't want to be the one supporting your code...
Jules Bean wrote on 22.06.2009 13:00:
Magnus Therning wrote:
Also from experience, I get a good feeling about software that
compiles without warnings. It suggests the author cares and is
indicative of some level of quality.
In contrast,
Jules Bean wrote on 22.06.2009 13:09:
Miguel Mitrofanov wrote:
I so don't want to be the one supporting your code...
Well, that's lucky. Because you aren't.
Exactly.
However, that's an easy arrow to fling. I say I don't find warnings
useful so you suggest my c
Well, I can make a bit more concrete prediction.
I'll download the problem, take a look, try for a while, discover,
that it's too hard to be cracked at once, and lose interest.
That sounds like a reason why I'm not participating.
On 23 Jun 2009, at 22:49, Rafael Gustavo da Cunha Pereira Pint
Well, without "fail" part:
newtype IOMayfail a = IOMayfail (MaybeT IO a) deriving Monad
Matthias Görgens wrote on 25.06.2009 17:14:
By the way, how would one write the following with Monad Transformers?
newtype IOMayfail a = IOMayfail (IO (Maybe a))
instance Monad IOMayfail where
retur
Sure:
newtype IOMayfail a = IOMayfail {runIOMayfail :: MaybeT IO a}
instance Monad IOMayfail where
return = IOMayfail . return
IOMayfail m >>= f = IOMayfail $ m >>= runIOMayfail . f
fail = whatever you like
Matthias Görgens wrote on 25.06.2009 17:28:
Thanks. Can I add something like fai
I was excited when I read about the VM - I'd imagined all sorts of
cool things, like assembler, linker, compiler (for something C-like),
maybe even debugger... And what a disappointment it was when I
understood that nothing of this kind is needed.
On 29 Jun 2009, at 22:55, John Meacham wrot
On 30 Jun 2009, at 00:03, John Meacham wrote:
The fact it didn't have any
looping meant that it wasn't even fully turing complete and you
probably
couldn't speed it up much anyway, it already had an intrinsically
short
running time.
Exactly! That's an ideal situation, you don't have to sp
You can do this if D -> M (N D) is a monad itself.
I suggest you study monad transformers - may be it's what you really
want.
On 10 Jul 2009, at 19:34, Job Vranish wrote:
I'm trying to make a function that uses another monadic function
inside a preexisting monad, and I'm having trouble.
Ba
I disagree. It was easy enough for me. OK, I do have some Category
Theory background and it certainly helps a lot. Still, I think that for
a beginner (without any experience with C or anything like that) Haskell
would be relatively easy. It doesn't involve (at least at the start) an
ugly notion
Domain theory semantics, I guess.
I know, that if I (or rather a younger copy of me, not knowing a thing
about Haskell) would be one of your students, and you tell me that there
is such a clean and nice semantics for what we are doing, I'd be excited.
Patai Gergely wrote:
Hello all,
I was a
Sufficient, but not good.
Try zippers instead.
On 15 Jul 2009, at 08:29, John Ky wrote:
Hello,
Actually, I wanted to be able to create a tree structure when I can
navigate both leaf-ward and root-ward. I didn't actually care for
equality.
I think the tying the knot technique as mention
No. Most constructors are functions, e.g. Just :: a -> Maybe a - a function.
On the other hand, Nothing :: Maybe a is a constructor, but not a function.
Andrew Wagner wrote:
Err, technically, aren't functions and constructors mutually exclusive?
So if something is a function, it's, by definitio
Consider the following expression:
(foo True, foo 'x')
Is this expression well-typed?
Astonishingly, the answer depends on where "foo" is defined. If
"foo" is a local variable, then the above expression is guaranteed
to be ill-typed. However, if we have (for example)
That's not true:
mai
What is it for? Yes, you would know that only A and B are Public, but
you have no way of telling that to the compiler.
I usually prefer something like that:
class Public x where
blah :: ...
isAB :: forall y. (A -> y) -> (B -> y) -> x -> y
Both solutions, however, allow the user to declare som
Oops... Sorry, wrong line. Should be
isAB :: forall p. p A -> p B -> p x
On 18 Jul 2009, at 10:51, Miguel Mitrofanov wrote:
What is it for? Yes, you would know that only A and B are Public,
but you have no way of telling that to the compiler.
I usually prefer something like that:
On 18 Jul 2009, at 13:26, Wolfgang Jeltsch wrote:
Am Samstag, 18. Juli 2009 06:31 schrieben Sie:
On Jul 18, 2009, at 2:35 AM, Wolfgang Jeltsch wrote:
So I should upload a package with German identifiers to Hackage?
Sure, why not? The fact that I can't read it is my loss, not your
fault,
a
On 18 Jul 2009, at 16:49, Wolfgang Jeltsch wrote:
Am Samstag, 18. Juli 2009 08:58 schrieb Miguel Mitrofanov:
Oops... Sorry, wrong line. Should be
isAB :: forall p. p A -> p B -> p x
Is this a well-known approach for closing classes?
I have an impression that this is kinda folklore.
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