[Haskell-cafe] shadowing keywords like otherwise
Hello,
I am currently using ghc 6.8.2. With the following,
swishParse :: String - String - SwishStateIO (Maybe RDFGraph)
swishParse fnam inp =
do { fmt - gets $ format
; case fmt of
N3- swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show fmt)) 4
; return Nothing
}
}
I am receiving a shadow warning:
Swish/HaskellRDF/SwishCommands.hs:304:12:
Warning: Defined but not used: `otherwise'
It seems to me that in the code base somewhere that there is a redefine of
the keywordotherwise. I haven't read the Haskell 98 Report but I thought
that it was not possible to redefine keywords. ??
Kind regards,
Vasili
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Re: [Haskell-cafe] shadowing keywords like otherwise
Vasili I. Galchin wrote: It seems to me that in the code base somewhere that there is a redefine of the keywordotherwise. I haven't read the Haskell 98 Report but I thought that it was not possible to redefine keywords. ?? otherwise is not a keyword. It is just defined as a normal function like so: otherwise = True Ciao, Janis. -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:vo...@tcs.inf.tu-dresden.de ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A Reader Monad Tutorial
On Sun, Jun 28, 2009 at 12:41 AM, Henry Laxennadine.and.he...@pobox.com wrote: Dear Group, If any of you are struggling with understanding monads, I've tried to put together a pretty through explanation of what is behind the Reader monad. If you're interested, have a look at: http://www.maztravel.com/haskell/readerMonad.html Nice post. I didn't find how to add comments on your blog, so I post them here: Areas of Confusion 1. What is the relationship between the Reader on the left hand side of the equals sign in the newtype definition and the Reader on the right hand side? 2. Why is there a Record field on the right hand side? 3. What is that r - a doing there? 1) Reader on the left hand side be called a type constructor, Reader on the right hand side be called a data constructor, in Haskell 98 Report. You call them type definition and instance constructor, respectively, I'm not sure it's a good idea, or it is right. bug in the explanation: what you use to make something and instance of a Reader (left hand side) - what you use to make something an instance of a Reader (left hand side) 2) runReader be called a selector function in Haskell 98 Report. 3) (-) is a type constructor, so r - a is a function type. I used found 'instance Monad ((-) r)' hard to understand, but by follow the hit given by Brent Yorgey, i.e. the data constructor for type constructor (-) is called lambda abstraction, I found I can understand them by type inference. I have written a post about how I figure it out, maybe you want take a look: http://leeduhem.wordpress.com/2009/06/07/understanding-monad-instance-by-type-inference/ bug in the explanation after (Reader f1) = f2 = Reader $ \e - runReader (Reader b) e: Reader b is a function that takes and e and returns a c, - Reader b is a function that takes an e and returns a c, lee ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] shadowing keywords like otherwise
Vasili I. Galchin wrote:
so Janis I have to look where the original author overrode otherwise?
If so, just great .. a ton of code. ;^(
No, you don't have to look for this. It is in the code snippet you sent:
swishParse :: String - String - SwishStateIO (Maybe RDFGraph)
swishParse fnam inp =
do { fmt - gets $ format
; case fmt of
N3- swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show
fmt)) 4
; return Nothing
}
}
In the case expression you use otherwise as a variable. But you do not
use that variable in that branch. Hence the warning:
Swish/HaskellRDF/SwishCommands.hs:304:12:
Warning: Defined but not used: `otherwise'
This has nothing to do with someone else shadowing the definition of
otherwise.
Ciao,
Janis.
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http://wwwtcs.inf.tu-dresden.de/~voigt/
mailto:vo...@tcs.inf.tu-dresden.de
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Re: [Haskell-cafe] shadowing keywords like otherwise
Hi Vasili,
This isn't really a shadowing/redefinition issue. Here's
a perfectly legitimate snippet that compiles fine:
f 0 = 0
f otherwise = 1+otherwise
Redefinition is when you have:
g = let otherwise = not in x
-- Kim-Ee
VasiliIGalchin wrote:
swishParse :: String - String - SwishStateIO (Maybe RDFGraph)
swishParse fnam inp =
do { fmt - gets $ format
; case fmt of
N3- swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show fmt))
4
; return Nothing
}
}
I am receiving a shadow warning:
Swish/HaskellRDF/SwishCommands.hs:304:12:
Warning: Defined but not used: `otherwise'
It seems to me that in the code base somewhere that there is a redefine
of
the keywordotherwise. I haven't read the Haskell 98 Report but I thought
that it was not possible to redefine keywords. ??
--
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Re: [Haskell-cafe] shadowing keywords like otherwise
I meant, of course,
g = let otherwise = not in otherwise
Sorry for the noise.
-- Kim-Ee
Kim-Ee Yeoh wrote:
Hi Vasili,
This isn't really a shadowing/redefinition issue. Here's
a perfectly legitimate snippet that compiles fine:
f 0 = 0
f otherwise = 1+otherwise
Redefinition is when you have:
g = let otherwise = not in x
-- Kim-Ee
VasiliIGalchin wrote:
swishParse :: String - String - SwishStateIO (Maybe RDFGraph)
swishParse fnam inp =
do { fmt - gets $ format
; case fmt of
N3- swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show
fmt)) 4
; return Nothing
}
}
I am receiving a shadow warning:
Swish/HaskellRDF/SwishCommands.hs:304:12:
Warning: Defined but not used: `otherwise'
It seems to me that in the code base somewhere that there is a redefine
of
the keywordotherwise. I haven't read the Haskell 98 Report but I
thought
that it was not possible to redefine keywords. ??
--
View this message in context:
http://www.nabble.com/%22shadowing%22-keywords-like-%22otherwise%22-tp24239153p24239439.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
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Re: [Haskell-cafe] shadowing keywords like otherwise
Hello Vasili,
Sunday, June 28, 2009, 10:39:37 AM, you wrote:
; case fmt of
N3 - swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show fmt)) 4
; return Nothing
}
}
first, otherwise aka True is used in *condition* part of case
statement. here you should use _
second, otherwise isn't a keyword, just a Prelude definition. here,
you assign fmt value to this identifier
--
Best regards,
Bulatmailto:bulat.zigans...@gmail.com
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Re: [Haskell-cafe] Rigid type variable error
On Sat, Jun 27, 2009 at 10:45 PM, Darryn djr...@aapt.net.au wrote:
Thanks for the help previously received, but I still cannot seem to get
on top of this. The types for the constructor K will not resolve and
I'm at a loss to work out what to do with it. If anyone can offer
a further explanation and help I would be very grateful.
My code (File Test5.hs):
{-# LANGUAGE ExistentialQuantification #-}
class A a where
a1 :: a
a2 :: a - a
a3 :: (B b) = b - a
class B b where
b1 :: Int - b
--data Ainst b = I | J (Ainst b) | K b
-- a3 :: (B b, A a) = b - a
-- yet without the constraint on K, K :: b - Ainst b
-- so the above data definition fails. Trying to
-- existentially quantify K below seems to make
-- sense, but also fails ...
data Ainst b = I | J (Ainst b) | (B b) = K b
instance (B b) = A (Ainst b) where
a1 = I
a2 = J
a3 = K -- Reported line of the error
data Binst = Val Int
instance B Binst where
b1 = Val
---
The error from ghci is as follows:
Test5.hs:25:9:
Couldn't match expected type `b' against inferred type `b1'
`b' is a rigid type variable bound by
the type signature for `a3' at Test5.hs:7:13
`b1' is a rigid type variable bound by
the instance declaration at Test5.hs:16:12
Expected type: b - Ainst b1
Inferred type: b1 - Ainst b1
In the expression: K
In the definition of `a3': a3 = K
Failed, modules loaded: none.
Thanks in advance for any help. Apologies if what I am doing is odd or
the answer is obvious, I'm still very new to Haskell.
The actual problem is not that easy to understand until you really get to
know the intricacies of Haskell's type checking. Do you think you could
explain your problem is less abstract terms? That is, sometimes if you tell
people here what you want to do and why they can suggest a better approach.
One thing to understand about your type class `A' is that it does not give a
relationship between `b' and `a'. As far as the definition of `A' is
concerned, `b' is totally arbitrary, so long as it is an instance of `B'.
In particular, no relationship with `a' is implied. Additionally, I'm
nearly certain that existential types are not needed or even wanted here.
K :: b - Ainst b
In particular, the `b' that `K' takes becomes part of the type that `K'
returns. This is different than the type of `a3'. In the type of `a3', the
`b' that it takes doesn't necessarily become part of the return type. In a
way, that means that `K' is less polymorphic than `a3'. This may not seem
like a problem, but it is what prevents `K' from having the same type as
`a3', and thus you get your error message. The type of `a3' is more general
than the type of `K' due to the possible ranges of the type variables
involved.
I have played with it a bit and found that this does compile:
\begin{code}
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances, FlexibleContexts #-}
class A a b | b - a where
a1 :: a
a2 :: a - a
a3 :: (B b) = b - a
class B b where
b1 :: Int - b
data Ainst b = I | J (Ainst b) | K b
instance (B b) = A (Ainst b) b where
a1 = I
a2 = J
a3 = K -- Reported line of the error
data Binst = Val Int
instance B Binst where
b1 = Val
\end{code}
If you remove all the type class constraints you won't need the
FlexibleContexts, but it's also not hurting anything.
Here I am using the functional dependency between `a' and `b' that says,
once you fix the type of `b', you also fix the type of `a'. You'll notice
that, that is exactly what `K' does. Given a `b', it gives you `Ainst a',
where `a = b', and therefore the type depends on, or is fixed by, `b'.
Multi parameter type classes are needed just so we can give the functional
dependency and the flexible things are in there just to work around Haskell
98 restrictions.
I hope this sheds more light on the problem. I bet you could be using type
families here as well, but I have yet to take the time to understand them.
I hope that helps,
Jason
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Re: [Haskell-cafe] Rigid type variable error
Am Sonntag 28 Juni 2009 07:45:33 schrieb Darryn:
Thanks for the help previously received, but I still cannot seem to get
on top of this. The types for the constructor K will not resolve and
I'm at a loss to work out what to do with it. If anyone can offer
a further explanation and help I would be very grateful.
My code (File Test5.hs):
{-# LANGUAGE ExistentialQuantification #-}
class A a where
a1 :: a
a2 :: a - a
a3 :: (B b) = b - a
This means a3 has the type
forall c. (B c) = c - a
class B b where
b1 :: Int - b
--data Ainst b = I | J (Ainst b) | K b
-- a3 :: (B b, A a) = b - a
-- yet without the constraint on K, K :: b - Ainst b
-- so the above data definition fails. Trying to
-- existentially quantify K below seems to make
-- sense, but also fails ...
data Ainst b = I | J (Ainst b) | (B b) = K b
Tis means K can only take an argument of type b, so
K :: (B b) = b - Ainst b
instance (B b) = A (Ainst b) where
a1 = I
a2 = J
a3 = K -- Reported line of the error
a3 must have type
forall c. (B b, B c) = c - Ainst b
which is more general than K's type.
Depending on what you want to do, you could
a) change Ainst,
data Ainst = I | J Ainst | (B b) = K b
instance (B b) = A Ainst where
a1 = I
a2 = J
a3 = K
but then you don't know what type b has been used to construct J (K x), so you
can't do
much with it.
b) make A a multiparameter type class with functional dependencies
class A a b | a - b where
a1 :: a
a2 :: a - a
a3 :: b - a
instance (B b) = A (Ainst b) b where
a1 = I
a2 = J
a3 = K
c) use type families:
class A a where
type S a
a1 :: a
a2 :: a - a
a3 :: S a - a
instance (B b) = A (Ainst b) where
type S (Ainst b) = b
a1 = I
a2 = J
a3 = K
b) and c) are more or less equivalent and restrict the type of a3 to K's type
data Binst = Val Int
instance B Binst where
b1 = Val
---
The error from ghci is as follows:
Test5.hs:25:9:
Couldn't match expected type `b' against inferred type `b1'
`b' is a rigid type variable bound by
the type signature for `a3' at Test5.hs:7:13
`b1' is a rigid type variable bound by
the instance declaration at Test5.hs:16:12
Expected type: b - Ainst b1
Inferred type: b1 - Ainst b1
In the expression: K
In the definition of `a3': a3 = K
Failed, modules loaded: none.
Thanks in advance for any help. Apologies if what I am doing is odd or
the answer is obvious, I'm still very new to Haskell.
Darryn.
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[Haskell-cafe] Re: test-framework success
2009/6/28 Simon Michael si...@joyful.com: But, I can now add -j8 and get the same results output in.. 0.13s. This quite surprised me, and now I want to say: thank you very much! :) Awesome! I'm really glad to hear you are having success with the package! For anyone else on the list who wants to take a look, the package home page is at http://batterseapower.github.com/test-framework/ Cheers, Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: FFI and heap memory usage limit
On Friday 26 June 2009, Simon Marlow wrote: Maybe bzlib allocates using malloc()? That would not be tracked by GHC's memory management, but could cause OOM. probably, because it's a binding to a C library. I'm really busy right now, but I'll try and create a small program to repro this error. Another problem is that if you ask for a large amount of memory in one go, the request is usually honoured immediately, and then we GC shortly afterward. If this is the problem for you, please submit a ticket and I'll see whether it can be changed. You could work around it by calling System.Mem.performGC just before allocating the memory. I've already worked around the problem. -- Marcin Kosiba signature.asc Description: This is a digitally signed message part. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] shadowing keywords like otherwise
On Sun, Jun 28, 2009 at 12:49:12AM -0700, Kim-Ee Yeoh wrote: This isn't really a shadowing/redefinition issue. Here's a perfectly legitimate snippet that compiles fine: f 0 = 0 f otherwise = 1+otherwise What? It is a redefinition issue *as well*, but this kind of warning isn't active by default Prelude :s -Wall Prelude let f 0 = 0; f otherwise = 1 + otherwise interactive:1:15: Warning: This binding for `otherwise' shadows the existing binding imported from Prelude In the definition of `f' -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Half-integer
I just wrote a small module for dealing with half-integers. (That is, any number I/2 where I is an integer. Note that the set of integers is a subset of this; Wikipedia seems to reserve half-integer for such numbers that are *not* integers.) module HalfInteger where data HalfInteger i instance (Eq i) = Eq (HalfInteger i) instance (Ord i) = Ord (HalfInteger i) instance (Integral i) = Show (HalfInteger i) instance (Integral i) = Num (HalfInteger i) half :: (Num i) = HalfInteger i fromNum :: (Integral i, RealFrac x) = x - HalfInteger i toNum :: (Integral i, Fractional x) = HalfInteger i - x isInteger :: (Integral i) = HalfInteger i - Bool Note carefully that the set of half-integers is *not* closed under multiplication! This means that for certain arguments, there are two reasonable products that could be returned. (E.g., 1/2 * 1/2 = 1/4, so 0 or 1/2 would be a reasonable rounding.) I haven't put a lot of effort into the rounding details of (*) or fromNum; which answer you get is kind of arbitrary. (However, addition and subtraction are exact, and for multiplications where an exact result is possible, you will get that result.) The Show instance outputs strings such as fromInteger 5 fromInteger 5 + half fromInteger (-5) - half depending on the isInteger predicate. Now, the question is... Is this useful enough to be worth putting on Hackage? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
On Sun, Jun 28, 2009 at 02:24:30PM +0100, Andrew Coppin wrote: Now, the question is... Is this useful enough to be worth putting on Hackage? Why not? :) -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Felipe Lessa wrote: On Sun, Jun 28, 2009 at 02:24:30PM +0100, Andrew Coppin wrote: Now, the question is... Is this useful enough to be worth putting on Hackage? Why not? :) Just upload it! I mean, at any point in time most package on hackage will be useless _to_me_. That doesn't mean they won't become useful in the future, and it certainly doesn't mean that someone else won't find them useful right now. :-) /M -- Magnus Therning(OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
On Sun, Jun 28, 2009 at 15:24, Andrew Coppinandrewcop...@btinternet.com wrote: I just wrote a small module for dealing with half-integers. (That is, any number I/2 where I is an integer. Note that the set of integers is a subset of this; Wikipedia seems to reserve half-integer for such numbers that are *not* integers.) module HalfInteger where data HalfInteger i instance (Eq i) = Eq (HalfInteger i) instance (Ord i) = Ord (HalfInteger i) instance (Integral i) = Show (HalfInteger i) instance (Integral i) = Num (HalfInteger i) half :: (Num i) = HalfInteger i fromNum :: (Integral i, RealFrac x) = x - HalfInteger i toNum :: (Integral i, Fractional x) = HalfInteger i - x isInteger :: (Integral i) = HalfInteger i - Bool Note carefully that the set of half-integers is *not* closed under multiplication! This means that for certain arguments, there are two reasonable products that could be returned. (E.g., 1/2 * 1/2 = 1/4, so 0 or 1/2 would be a reasonable rounding.) I haven't put a lot of effort into the rounding details of (*) or fromNum; which answer you get is kind of arbitrary. (However, addition and subtraction are exact, and for multiplications where an exact result is possible, you will get that result.) The Show instance outputs strings such as fromInteger 5 fromInteger 5 + half fromInteger (-5) - half depending on the isInteger predicate. Now, the question is... Is this useful enough to be worth putting on Hackage? Out of curiosity, what are *you* using it for? Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: A Reader Monad Tutorial
Lee Duhem lee.duhem at gmail.com writes: Nice post. I didn't find how to add comments on your blog, so I post them here: ... Dear Lee, Thank you for your comments and corrections. I have included all of them in the new version of the article. Best wishes, Henry Laxen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Thomas ten Cate wrote: Out of curiosity, what are *you* using it for? Centering things. In you have an odd number of items, the middle one will be at position 0, with the others at integer positions on either side. However, if you have an even number, the middle two will be at 0 +- 1/2, and so forth. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Felipe Lessa wrote: On Sun, Jun 28, 2009 at 02:24:30PM +0100, Andrew Coppin wrote: Now, the question is... Is this useful enough to be worth putting on Hackage? Why not? :) Well, it *does* mean I'll have to figure out how Cabal actually works... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] What is an expected type ...
as opposed to an inferred type? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
Hi Michael, michael rice wrote: as opposed to an inferred type? Can you deduce from the following example? Prelude let foo = () :: Int interactive:1:10: Couldn't match expected type `Int' against inferred type `()' In the expression: () :: Int In the definition of `foo': foo = () :: Int Hope this helps! Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
When Haskell runs it's type checker, it tries to guess the type of each function. Thats why you can write: map (+1) and it knows that you're talking about a function of type: Num a = [a] - [a] Another thing, called 'defaulting' resolves this, but you didn't ask about that, so I won't go into it. An expected type is one that you provide to the compiler in the form of a type signature, this can be used to specialize a general type (like the one I showed) or to resolve ambiguous types the compiler can't, or just for documentation/good practice. So when I write: foo :: Num a = [a] - [a] foo ls = map (+1) ls The expected type for `foo` is `Num a = [a] - [a]`. I imagine you're asking this because you got an error which said your expected type doesn't match your inferred type. That might, for instance, happen if I wrote: bar :: String bar = 'a' 'a' has type `Char`, since `String` is not `Char`, the type checker infers that 'a' has type char, but _expects_ it to be type String. Two solutions are as follows: --- Method 1 bar :: Char bar = 'a' --- Method 2 bar :: String bar = a Can you see why those two changes fix the problem? Also, just as a matter of process, I forwarded this to the haskell-beginners list, as I imagine type errors like these come up a lot, and someone probably has a better explanation over there. /Joe michael rice wrote: as opposed to an inferred type? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe begin:vcard fn:Joseph Fredette n:Fredette;Joseph adr:Apartment #3;;6 Dean Street;Worcester;Massachusetts;01609;United States of America email;internet:jfred...@gmail.com tel;home:1-508-966-9889 tel;cell:1-508-254-9901 x-mozilla-html:FALSE url:lowlymath.net, humbuggery.net version:2.1 end:vcard ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] shadowing keywords like otherwise
On Jun 28, 2009, at 02:39 , Vasili I. Galchin wrote:
; case fmt of
N3- swishParseN3 fnam inp
otherwise -
do { swishError (Unsupported file format: ++(show
fmt)) 4
; return Nothing
}
}
I am receiving a shadow warning:
Swish/HaskellRDF/SwishCommands.hs:304:12:
Warning: Defined but not used: `otherwise'
1. otherwise isn't a keyword, it's a function (well, CAF).
2. if you use a variable in a case alternative, that variable is
created and bound. I think you wanted to use _ instead of
otherwise there.
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Re: [Haskell-cafe] What is an expected type ...
On Jun 28, 2009, at 12:02 , michael rice wrote: dec2bin :: Integer - [Integer] dec2bin n = dec2bin' n [] where dec2bin' n acc | n == 0 = acc | otherwise = let r = rem n 2 m = div (n - r) 2 in dec2bin' m (r : acc) is there any way to assign a type signature to the helper function? Same way you do for a top level binding: dec2bin :: Integer - [Integer] dec2bin n = dec2bin' n [] where dec2bin' :: Integer - [Integer] - [Integer] dec2bin' n acc | n == 0 = acc | otherwise = let r = rem n 2 m = div (n - r) 2 in dec2bin' m (r : acc) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
2009/6/28 Andrew Coppin andrewcop...@btinternet.com: Felipe Lessa wrote: On Sun, Jun 28, 2009 at 02:24:30PM +0100, Andrew Coppin wrote: Now, the question is... Is this useful enough to be worth putting on Hackage? Why not? :) Well, it *does* mean I'll have to figure out how Cabal actually works... Usually, it's pretty straight-forward and most options are self-explanatory. http://en.wikibooks.org/wiki/Haskell/Packaging#The_Cabal_file -- Deniz Dogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
Hey Joe, all, Got it. Thanks! An associated question: In programming a local helper or auxilliary function such as dec2bin' in dec2bin :: Integer - [Integer] dec2bin n = dec2bin' n [] where dec2bin' n acc | n == 0 = acc | otherwise = let r = rem n 2 m = div (n - r) 2 in dec2bin' m (r : acc) is there any way to assign a type signature to the helper function? Michael --- On Sun, 6/28/09, Joe Fredette jfred...@gmail.com wrote: From: Joe Fredette jfred...@gmail.com Subject: Re: [Haskell-cafe] What is an expected type ... To: michael rice nowg...@yahoo.com Cc: Haskell Cafe mailing list haskell-cafe@haskell.org, beginn...@haskell.org Date: Sunday, June 28, 2009, 11:29 AM When Haskell runs it's type checker, it tries to guess the type of each function. Thats why you can write: map (+1) and it knows that you're talking about a function of type: Num a = [a] - [a] Another thing, called 'defaulting' resolves this, but you didn't ask about that, so I won't go into it. An expected type is one that you provide to the compiler in the form of a type signature, this can be used to specialize a general type (like the one I showed) or to resolve ambiguous types the compiler can't, or just for documentation/good practice. So when I write: foo :: Num a = [a] - [a] foo ls = map (+1) ls The expected type for `foo` is `Num a = [a] - [a]`. I imagine you're asking this because you got an error which said your expected type doesn't match your inferred type. That might, for instance, happen if I wrote: bar :: String bar = 'a' 'a' has type `Char`, since `String` is not `Char`, the type checker infers that 'a' has type char, but _expects_ it to be type String. Two solutions are as follows: --- Method 1 bar :: Char bar = 'a' --- Method 2 bar :: String bar = a Can you see why those two changes fix the problem? Also, just as a matter of process, I forwarded this to the haskell-beginners list, as I imagine type errors like these come up a lot, and someone probably has a better explanation over there. /Joe michael rice wrote: as opposed to an inferred type? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Deniz Dogan wrote: 2009/6/28 Andrew Coppin andrewcop...@btinternet.com: Felipe Lessa wrote: On Sun, Jun 28, 2009 at 02:24:30PM +0100, Andrew Coppin wrote: Now, the question is... Is this useful enough to be worth putting on Hackage? Why not? :) Well, it *does* mean I'll have to figure out how Cabal actually works... Usually, it's pretty straight-forward and most options are self-explanatory. http://en.wikibooks.org/wiki/Haskell/Packaging#The_Cabal_file Yes, one would *hope* that a 1-module library with no dependencies would be fairly trivial. ;-) Also Haddock; I'm thinking some documentation might be nice... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
How else? ;-) Thanks, Michael --- On Sun, 6/28/09, Brandon S. Allbery KF8NH allb...@ece.cmu.edu wrote: From: Brandon S. Allbery KF8NH allb...@ece.cmu.edu Subject: Re: [Haskell-cafe] What is an expected type ... To: michael rice nowg...@yahoo.com Cc: Brandon S. Allbery KF8NH allb...@ece.cmu.edu, Joe Fredette jfred...@gmail.com, beginn...@haskell.org, Haskell Cafe mailing list haskell-cafe@haskell.org Date: Sunday, June 28, 2009, 12:06 PM On Jun 28, 2009, at 12:02 , michael rice wrote:dec2bin :: Integer - [Integer] dec2bin n = dec2bin' n [] where dec2bin' n acc | n == 0 = acc | otherwise = let r = rem n 2 m = div (n - r) 2 in dec2bin' m (r : acc) is there any way to assign a type signature to the helper function? Same way you do for a top level binding: dec2bin :: Integer - [Integer] dec2bin n = dec2bin' n [] where dec2bin' :: Integer - [Integer] - [Integer] dec2bin' n acc | n == 0 = acc | otherwise = let r = rem n 2 m = div (n - r) 2 in dec2bin' m (r : acc) -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.comsystem administrator [openafs,heimdal,too many hats] allb...@ece.cmu.eduelectrical and computer engineering, carnegie mellon university KF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
Am Sonntag 28 Juni 2009 18:06:52 schrieb Brandon S. Allbery KF8NH:
On Jun 28, 2009, at 12:02 , michael rice wrote:
dec2bin :: Integer - [Integer]
dec2bin n = dec2bin' n []
where dec2bin' n acc
| n == 0 = acc
| otherwise = let r = rem n 2
m = div (n - r) 2
in dec2bin' m (r : acc)
is there any way to assign a type signature to the helper function?
Same way you do for a top level binding:
dec2bin :: Integer - [Integer]
dec2bin n = dec2bin' n []
where dec2bin' :: Integer - [Integer] - [Integer]
dec2bin' n acc
| n == 0 = acc
| otherwise = let r = rem n 2
m = div (n - r) 2
in dec2bin' m (r : acc)
But, to mention it before it bites, putting type signatures involving type
variables on
local helper functions is not entirely straightforward. Consider
inBase :: Integral a = a - a - [a]
0 `inBase` b = [0]
n `inBase` b = local n []
where
local 0 acc = acc
local m acc = case m `divMod` b of
(q,r) - local q (r:acc)
Now try giving a type signature to local. You can't.
What is the type of local?
It's (type of b) - [type of b] - [type of b],
but type of b isn't available.
If you try
local :: a - [a] - [a]
or
local :: Integral a = a - [a] - [a],
you are saying that local works for *every* type a (or for every type a which
is an
instance of Integral), because the 'a' from local's type signature is a new
(implicitly
forall'd) type variable.
To be able to give local a type signature, you must bring the type variable 'a'
into
scope:
{-# LANGUAGE ScopedTypeVariables #-}
inBase :: forall a. Integral a = a - a - [a]
0 `inBase` b = [0]
n `inBase` b = local n []
where
local :: a - [a] - [a]-- now this a is the same a as the one above
local 0 acc = acc
local m acc = case m `divMod` b of
(q,r) - local q (r:acc)
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Re: [Haskell-cafe] What is an expected type ...
On Sun, Jun 28, 2009 at 17:14, michael ricenowg...@yahoo.com wrote: as opposed to an inferred type? There was a thread on haskell-cafe about this a few weeks ago. Here it is in the archives: http://www.haskell.org/pipermail/haskell-cafe/2009-May/062012.html Maybe some post in there might help. Maybe they will all confuse you... :) Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: X Haskell Bindings 0.3
I'd like to announce the 0.3.* series release of the X Haskell Bindings. This release, like the prior 0.2.* series focuses on making the API prettier. This release is based on the XCB protocol descriptions version 1.5 This does mean that there's a good chance this is a breaking release for any code compiled against 0.2.*. The goal of XHB is to provide a Haskell implementation of the X11 wire protocol, similar in spirit to the X protocol C-language Binding (XCB). On Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhb Source: darcs get http://community.haskell.org/~aslatter/code/xhb/ New this release: * In 0.2, a lot of the core protocol requests, events and replies were updated to use prettier Haskell datatypes for the various enums and bitmasks. Thanks to Peter Harris's work on the protocol description XML files, these niceties have extended out to all of the extension requests, events and replies and such. * Due to name clashes, I the type-names for events and errors now include an Event or Error suffix. For example, the type Notify has become NotifyEvent. * Now based on the protocol description version 1.5, from 1.4. Related projects: X protocol C-language Binding: http://xcb.freedesktop.org/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANNOUNCE: X Haskell Bindings 0.3
On Sun, Jun 28, 2009 at 12:52 PM, Antoine Latteraslat...@gmail.com wrote: I'd like to announce the 0.3.* series release of the X Haskell Bindings. This release, like the prior 0.2.* series focuses on making the API prettier. This release is based on the XCB protocol descriptions version 1.5 I'd also like to share my thoughts on where the XHB project is, and where I see it going. As an experiment to show that an X client library can be written in Haskell, I feel like XHB has succeeded. But to be truly useful as a library, I feel like it needs to be able to inter-operate with xlib and libxcb, which XHB currently does not. Conceptually, XHB can be thought of as two parts: - Haskell data types generated from the X protocol description, which know how to serilaize/deserialize themselves to and from byte streams. - A runtime which knows how to open a connection to the X server, and knows how to peek and poke stuff onto the connection to the X server (this is where all of the networking and thread wrangling code lives). So it seems to me that the path forward is to keep as much of the first part as possible, and then replace the second part with haskell bindings to XCB. I've started the binding to libxcb here: http://community.haskell.org/~aslatter/code/xcb-ffi/ There are still a few unknowns in my mind, such as - I've never made Haskell bindings to a multi-threaded C App. Is there anything strange I have to worry about? - I have no idea how I'll map event and error codes to the function to decode the bytes into a Haskell type. In XHB all of the information needed lives in Haskell datatypes - once I start moving over to being a wrapper around XCB, the extensions cache is held in libxcb and isn't exposed publicly. But presumably these problems have solutions. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
I really dislike this error message, and I think the terms are ambiguous. I think the words 'expected' and 'inferred' apply equally well to the term, and the context in which it has been found. Both of the incompatible types were 'inferred', and 'unexpected' is a property of the combination, not a property of one or the other. -- Dan On Sun, Jun 28, 2009 at 8:24 AM, Martijn van Steenbergenmart...@van.steenbergen.nl wrote: Hi Michael, michael rice wrote: as opposed to an inferred type? Can you deduce from the following example? Prelude let foo = () :: Int interactive:1:10: Couldn't match expected type `Int' against inferred type `()' In the expression: () :: Int In the definition of `foo': foo = () :: Int Hope this helps! Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Andrew Coppin wrote: Deniz Dogan wrote: 2009/6/28 Andrew Coppin andrewcop...@btinternet.com: Well, it *does* mean I'll have to figure out how Cabal actually works... Usually, it's pretty straight-forward and most options are self-explanatory. http://en.wikibooks.org/wiki/Haskell/Packaging#The_Cabal_file Yes, one would *hope* that a 1-module library with no dependencies would be fairly trivial. ;-) Ah, but it's not as easy as you'd think. The instructions above fail to mention several required or strongly recommended fields. (E.g., apparently Category and Synopsis are both required, Cabal-Version is strongly recommended, several fields are meant to be in the Library subsection...) And then of course there's the question of choosing a licence. But I think I'm nearly there now. Oh, one last thing. I know I'm going to regret this for the rest of my life, but... which version of Base should it depend on? Also Haddock; I'm thinking some documentation might be nice... This at least *was* fairly trivial. ;-) [The only hard part being figuring out how to manually run Haddock...] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
On Sun, Jun 28, 2009 at 2:13 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Oh, one last thing. I know I'm going to regret this for the rest of my life, but... which version of Base should it depend on? Which versions of base have you tested it with? :-) Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
Antoine Latter wrote: On Sun, Jun 28, 2009 at 2:13 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Oh, one last thing. I know I'm going to regret this for the rest of my life, but... which version of Base should it depend on? Which versions of base have you tested it with? :-) Whichever one GHC 6.10.3 ships with... Frankly, I highly doubt it makes any difference either way. (Does anybody know how base3 differs from base4?) It only uses a few type classes from the Prelude... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Half-integer
On Sun, Jun 28, 2009 at 9:29 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Which versions of base have you tested it with? :-) Whichever one GHC 6.10.3 ships with... ghc-pkg list base will tell you which version you have installed. Frankly, I highly doubt it makes any difference either way. (Does anybody know how base3 differs from base4?) It only uses a few type classes from the Prelude... If it *only* uses the prelude (i.e., does not include *any* modules), then it should work with any version of base. --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] shadowing keywords like otherwise
Whoops, you're right. Interestingly, the shadowing warnings vary between the 2 examples I gave, i.e. shadowing within 'function definition' vs 'binding group'. Felipe Lessa wrote: On Sun, Jun 28, 2009 at 12:49:12AM -0700, Kim-Ee Yeoh wrote: This isn't really a shadowing/redefinition issue. Here's a perfectly legitimate snippet that compiles fine: f 0 = 0 f otherwise = 1+otherwise What? It is a redefinition issue *as well*, but this kind of warning isn't active by default Prelude :s -Wall Prelude let f 0 = 0; f otherwise = 1 + otherwise interactive:1:15: Warning: This binding for `otherwise' shadows the existing binding imported from Prelude In the definition of `f' -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://www.nabble.com/%22shadowing%22-keywords-like-%22otherwise%22-tp24239153p24244760.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
Could you suggest a better word pair to describe the dichotomy then? How about 'calculated' vs 'user-imposed' (or even, 'explicitly- signatured')? Dan Piponi-2 wrote: I really dislike this error message, and I think the terms are ambiguous. I think the words 'expected' and 'inferred' apply equally well to the term, and the context in which it has been found. Both of the incompatible types were 'inferred', and 'unexpected' is a property of the combination, not a property of one or the other. -- Dan On Sun, Jun 28, 2009 at 8:24 AM, Martijn van Steenbergenmart...@van.steenbergen.nl wrote: Hi Michael, michael rice wrote: as opposed to an inferred type? Can you deduce from the following example? Prelude let foo = () :: Int interactive:1:10: Couldn't match expected type `Int' against inferred type `()' In the expression: () :: Int In the definition of `foo': foo = () :: Int Hope this helps! Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://www.nabble.com/What-is-an-%22expected-type%22-...-tp24242359p24244820.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] What is an expected type ...
Hello Kim-Ee, Sunday, June 28, 2009, 11:52:57 PM, you wrote: we already had a *long* discussion on this topic. afaik, it's dichotomy between type of term itself and type of position where it's used (f.e. argument of some function) Could you suggest a better word pair to describe the dichotomy then? How about 'calculated' vs 'user-imposed' (or even, 'explicitly- signatured')? Dan Piponi-2 wrote: I really dislike this error message, and I think the terms are ambiguous. I think the words 'expected' and 'inferred' apply equally well to the term, and the context in which it has been found. Both of the incompatible types were 'inferred', and 'unexpected' is a property of the combination, not a property of one or the other. -- Dan On Sun, Jun 28, 2009 at 8:24 AM, Martijn van Steenbergenmart...@van.steenbergen.nl wrote: Hi Michael, michael rice wrote: as opposed to an inferred type? Can you deduce from the following example? Prelude let foo = () :: Int interactive:1:10: Couldn't match expected type `Int' against inferred type `()' In the expression: () :: Int In the definition of `foo': foo = () :: Int Hope this helps! Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal fun [Half-integer]
Max Rabkin wrote: On Sun, Jun 28, 2009 at 9:29 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Which versions of base have you tested it with? :-) Whichever one GHC 6.10.3 ships with... ghc-pkg list base will tell you which version you have installed. Which tells me I have base-3.0.3.1 *and* base-4.1.0.0 ;-) Frankly, I highly doubt it makes any difference either way. (Does anybody know how base3 differs from base4?) It only uses a few type classes from the Prelude... If it *only* uses the prelude (i.e., does not include *any* modules), then it should work with any version of base. Yeah, that's what I figured... Alrighty then, so how I just do Setup configure, and now Setup sdist, and then I can upload the result to Ha-- oh, don't be silly. That would simply be too easy. ;-) E:\Haskell\AOC-HalfIntegerrunhaskell Setup sdist Building source dist for AOC-HalfInteger-1.0... Preprocessing library AOC-HalfInteger-1.0... Setup: tar is required but it could not be found. Time to go search the web and find out what the other 50 people who stumbled into this did... *sigh* ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is an expected type ...
Bulat Ziganshin wrote: Hello Kim-Ee, Sunday, June 28, 2009, 11:52:57 PM, you wrote: we already had a *long* discussion on this topic. afaik, it's dichotomy between type of term itself and type of position where it's used (f.e. argument of some function) Could you suggest a better word pair to describe the dichotomy then? How about 'calculated' vs 'user-imposed' (or even, 'explicitly- signatured')? How about 'Int' used in '()'-shaped hole? 'Int' from usage, '()' from definition of 'foo' could not be reconciled? Arne D Halvorsen Dan Piponi-2 wrote: I really dislike this error message, and I think the terms are ambiguous. I think the words 'expected' and 'inferred' apply equally well to the term, and the context in which it has been found. Both of the incompatible types were 'inferred', and 'unexpected' is a property of the combination, not a property of one or the other. -- Dan On Sun, Jun 28, 2009 at 8:24 AM, Martijn van Steenbergenmart...@van.steenbergen.nl wrote: Hi Michael, michael rice wrote: as opposed to an inferred type? Can you deduce from the following example? Prelude let foo = () :: Int interactive:1:10: Couldn't match expected type `Int' against inferred type `()' In the expression: () :: Int In the definition of `foo': foo = () :: Int Hope this helps! Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal fun [Half-integer]
Andrew Coppin wrote: Alrighty then, so how I just do Setup configure, and now Setup sdist, and then I can upload the result to Ha-- oh, don't be silly. That would simply be too easy. ;-) E:\Haskell\AOC-HalfIntegerrunhaskell Setup sdist Building source dist for AOC-HalfInteger-1.0... Preprocessing library AOC-HalfInteger-1.0... Setup: tar is required but it could not be found. Time to go search the web and find out what the other 50 people who stumbled into this did... *sigh* Ah. Apparently it's fixed: http://hackage.haskell.org/trac/hackage/ticket/40 Except that it isn't fixed. Yay for me... It seems that GHC provides ar but not tar. Looks like I might actually have to copy the entire directory tree to a Linux box just so I can run sdist... Nice to know this stuff is so easy. :-/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal fun [Half-integer]
On Sun, Jun 28, 2009 at 3:42 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Andrew Coppin wrote: Alrighty then, so how I just do Setup configure, and now Setup sdist, and then I can upload the result to Ha-- oh, don't be silly. That would simply be too easy. ;-) E:\Haskell\AOC-HalfIntegerrunhaskell Setup sdist Building source dist for AOC-HalfInteger-1.0... Preprocessing library AOC-HalfInteger-1.0... Setup: tar is required but it could not be found. Time to go search the web and find out what the other 50 people who stumbled into this did... *sigh* Ah. Apparently it's fixed: http://hackage.haskell.org/trac/hackage/ticket/40 Except that it isn't fixed. Yay for me... It seems that GHC provides ar but not tar. Looks like I might actually have to copy the entire directory tree to a Linux box just so I can run sdist... Nice to know this stuff is so easy. :-/ I don't know anything that's gauranteed to work, as I've never tried packaging from a Windows box, but: - Is 'htar' a good enough 'tar' replacement for cabal? - Does cabal-install also require an external tar? You could try cabal sdist Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: test-framework success
On Sun, Jun 28, 2009 at 11:07:27AM +0100, Max Bolingbroke wrote: Awesome! I'm really glad to hear you are having success with the package! BTW, thanks for fixing the spacing issue with nested tests! :) -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] C global vars local to threads
I would like to write a wrapper to C global variable, but that variable is unique to each thread. Is there some native support on that in Haskell FFI? (I imagine I probably should write a C function to get its pointer as an 'IO (Ptr ...)', but I would like to check if there's a more standard way to do that.) Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] parallel haskell
I'm interested in doing some research with parallel programming using Haskell (both multi-core on one machine and clusters using multiple machines) but in going through the various resources on the web (looking at GPH and others), it is not clear to me what the current state is as many of the resources/projects have out of date information in them. Any pointers ? What parallel extensions are available in the current version 6.10.3 ? Which parallel extensions support clustered networks ? Where to start ? Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal fun [Half-integer]
On Sun, Jun 28, 2009 at 4:11 PM, Antoine Latteraslat...@gmail.com wrote: On Sun, Jun 28, 2009 at 3:42 PM, Andrew Coppinandrewcop...@btinternet.com wrote: Andrew Coppin wrote: Alrighty then, so how I just do Setup configure, and now Setup sdist, and then I can upload the result to Ha-- oh, don't be silly. That would simply be too easy. ;-) E:\Haskell\AOC-HalfIntegerrunhaskell Setup sdist Building source dist for AOC-HalfInteger-1.0... Preprocessing library AOC-HalfInteger-1.0... Setup: tar is required but it could not be found. Time to go search the web and find out what the other 50 people who stumbled into this did... *sigh* Ah. Apparently it's fixed: http://hackage.haskell.org/trac/hackage/ticket/40 Except that it isn't fixed. Yay for me... It seems that GHC provides ar but not tar. Looks like I might actually have to copy the entire directory tree to a Linux box just so I can run sdist... Nice to know this stuff is so easy. :-/ I don't know anything that's gauranteed to work, as I've never tried packaging from a Windows box, but: - Is 'htar' a good enough 'tar' replacement for cabal? - Does cabal-install also require an external tar? You could try cabal sdist If one actually reads the discussion in the ticket, it is clear that the conclusion was to have cabal-install handle it and that cabal-install uses it's own tar implementation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] List spine traversal
Is there a canonical function for traversing the spine of a list? I could use e.g. (seq . length) but this feels dirty, so I have foldl' (const . const $ ()) () which still doesn't feel right. What's the typical means of doing this? -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] parallel haskell
k2msmith: I'm interested in doing some research with parallel programming using Haskell (both multi-core on one machine and clusters using multiple machines) but in going through the various resources on the web (looking at GPH and others), it is not clear to me what the current state is as many of the resources/projects have out of date information in them. Any pointers ? What parallel extensions are available in the current version 6.10.3 ? Which parallel extensions support clustered networks ? Where to start ? A broad overview of all the abstractions available: http://haskell.org/haskellwiki/Applications_and_libraries/Concurrency_and_parallelism Obviously, the most heavily used are those for shared-memory multicore implemented and shipping with GHC (see e.g. the new rts papers). Things like sparks, STM, MVars, and to some extent nested data parallelism, are just there, out of the box. A good paper on the rts support in GHC. http://ghcmutterings.wordpress.com/2009/03/03/new-paper-runtime-support-for-multicore-haskell/ Followed by hackage libraries for different things (like actors). Transparently distributed Haskell's are researchy, and someone else should fill in the story there. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Platform + gtk2hs
List, Has any one managed to install gtk2hs on a Windows box running the Haskell Platform? I've had no luck; it seems the gtk2hs installer is unable to find the GHC installation. /jve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to convert CPid to Word32?
Hi, I am trying to use Data.Binary with ProcessID. Well, how to convert between CPid and Word32? Thanks. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to convert CPid to Word32?
fromIntegral should do the trick. Thomas On Sun, Jun 28, 2009 at 7:48 PM, Magicloud Magicloudsmagicloud.magiclo...@gmail.com wrote: Hi, I am trying to use Data.Binary with ProcessID. Well, how to convert between CPid and Word32? Thanks. -- 竹密岂妨流水过 山高哪阻野云飞 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
