On Mon, 7 Apr 2008, Jackm139 wrote:
I'm new to Haskell, and I'm finding it is very different from any other
language I have worked with.
I have an assignment to make a program to test whether two lists use the
same characters for each string.
e.g.
sameCharacter ["rock", "cab"] ["cork", "abc"
apfelmus:
Manuel M T Chakravarty wrote:
Ganesh Sittampalam:
Let's alpha-rename the signatures and use explicit foralls for
clarity:
foo :: forall a. Id a -> Id a
foo' :: forall b. Id b -> Id b
GHC will try to match (Id a) against (Id b). As Id is a type
synonym family, it would *not* be
Hi Mark,
I don't know if you have defined/studied corresponding notions of
ambiguity/coherence in your framework. Instead, I was referring to
what Manuel described as "the equivalent problem using FDs":
class IdC a b | a -> b
instance IdC Int Int
bar :: IdC a b => b -> b
bar = id
bar' :
I don't know how to calibrate my response to what you are really asking
for. Depending on how "new" you are, maybe all you want is just "working
syntax" to get you started. Here is a structurally similar problem, if
it helps. (And if you are more advanced, try the extra credit!)
Find the "ave
Ganesh Sittampalam:
Can I have some advice on translating the attached Test1.hs into
type families? My attempt at doing so is in Test1a.hs, but firstly
it requires FlexibleInstances where Test1.hs didn't, and secondly it
fails because it can't infer the instance for Bar (Either Int Int)
wh
On Tue, Apr 8, 2008 at 1:51 PM, Jackm139 <[EMAIL PROTECTED]> wrote:
> I have an assignment to make a program to test whether two lists use the
> same characters for each string.
> e.g.
>
> sameCharacter ["rock", "cab"] ["cork", "abc"]
> True
I would start with something smaller: try defining
On Mon, Apr 07, 2008 at 07:51:05PM -0700, Jackm139 wrote:
> I have an assignment to make a program to test whether two lists use the
> same characters for each string.
> e.g.
>
> sameCharacter ["rock", "cab"] ["cork", "abc"]
> True
>
> My plan to tackle this was to use:
> nub to eliminate duplic
I'm new to Haskell, and I'm finding it is very different from any other
language I have worked with.
I have an assignment to make a program to test whether two lists use the
same characters for each string.
e.g.
sameCharacter ["rock", "cab"] ["cork", "abc"]
True
My plan to tackle this was to us
On 2008.04.07 20:17:06 +0200, ln <[EMAIL PROTECTED]> scribbled 1.1K characters:
> Hi,
>
> I would like to try HXT, but I can't manage to build it. I resolved all
> the dependencies, but I get the following error:
>
> > > [EMAIL PROTECTED]:~/Desktop/hxt$ make all
> > > make -C src all VERSION=7
On Monday 07 April 2008 5:57:39 pm [EMAIL PROTECTED] wrote:
> So almost certainly the issue is that HaXml has updated and changed things
> around in a way that broke Hpodder; not surprising, since HaXml-1.19.2 is
> as recent as 14 January 2008, and Goerzen may simply not have updated and
> discove
Actually, this even works without undecidable instances!
On 4/7/08, Ryan Ingram <[EMAIL PROTECTED]> wrote:
> {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
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The type system requires strong normalization. By specifying
"allow-undecidable-instances", you are agreeing to provide proofs of
strong normalization outside of the compiler, instead of relying on
the compiler to derive them for you.
Because you have claimed that your instance is strongly normal
Hi,
Thank you very much for your helpful replies.
So, we define (or is it declare) a class with a polymorphic value(s
which will be used in defining function types or functions associated
with that class. The data types are then used for deriving instances
of that class specific to each data ty
On 2008.04.07 00:24:10 +0200, Karl Hasselström <[EMAIL PROTECTED]> scribbled
0.9K characters:
> I'm trying to build hpodder 1.1.2 with ghc 6.8.2. I successfully
> downloaded, built, and installed (the latest versions of) all its
> dependencies, but when building hpodder itself, I get
>
> FeedParse
Hello Hans,
Tuesday, April 8, 2008, 2:28:53 AM, you wrote:
> At least Hugs complains if one does not indent "deriving ...", but I
> do not know what the standard says. If is required, then it can be
> changed.
deriving is a part of data clause and indentation just allows us to
continue clause
On 7 Apr 2008, at 21:48, Brandon S. Allbery KF8NH wrote:
But here, one would have to think about how the compiler should be
able to distinguish
data Bool = False | True
instance (Eq)
from
data Bool = False | True
instance Eq Bool where
x == y = ...
Layout already does that, doe
Hi Tom,
It seems we are thinking of different things. I was referring to
the characterization of a type of the form P => t as being "ambiguous"
if there is a type variable in P that is not determined by the
variables in t; this condition is used in Haskell to establish
coherence (i.e., to show t
The problem is that the representation probably does not reduce to a normal
form.
Say, for the case
type instance F (Nest a) x = Either() (a,F a x)
fnn :: F (Nest a) (Nest a)
fnn = Left ()
it compiles ok.
But why can't the representation be infinite, like any other infinite data
type?
Cheers,
h
Hi guys,
I have been experimenting some weird stuff (risky, yes I know) but the
behaviour was certainly not the one I expected:
{-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
module Nest where
data Nest a = Nil | Cons a (Nest (a,a))
type family F a x :: *
type instance F (Nest a)
Hi,
Can I have some advice on translating the attached Test1.hs into type
families? My attempt at doing so is in Test1a.hs, but firstly it requires
FlexibleInstances where Test1.hs didn't, and secondly it fails because it
can't infer the instance for Bar (Either Int Int) whereas the fundeps
v
> Id is an operation over types yielding a type, as such it doesn't make
> much sense to me to have (Id a -> Id a) but rather something like (a ->
> Id a).
Actually, it can make perfect sense: e.g. if the `Id' function acts as
a constraint.
Stefan
___
On Apr 7, 2008, at 15:42 , Hans Aberg wrote:
But here, one would have to think about how the compiler should be
able to distinguish
data Bool = False | True
instance (Eq)
from
data Bool = False | True
instance Eq Bool where
x == y = ...
Layout already does that, doesn't it? T
On 7 Apr 2008, at 21:15, Dan Weston wrote:
To answer your second question (which everyone else ignored):
Yes. A different keyword might have been more descriptive, such as
"automatically_deriving_instances_for".
They are called instantiations, which Haskell can supply
automatically in some
Paul,
To answer your second question (which everyone else ignored):
Yes. A different keyword might have been more descriptive, such as
"automatically_deriving_instances_for".
There is always a struggle between concision [1] and descriptiveness in
syntax. With short keywords, you pay up front
I meant to send this reply to the cafe.
- Forwarded message -
Date: Mon, 7 Apr 2008 15:05:00 -0400
To: PR Stanley <[EMAIL PROTECTED]>
Subject: Re: [Haskell-cafe] deriving
Paul,
> No, sorry. I'm not sure how this differs from my definition.
> Could you elaborate please?
Gladly.
On Mon, Apr 07, 2008 at 10:28:12PM +0400, Bulat Ziganshin wrote:
> Monday, April 7, 2008, 9:22:25 PM, you wrote:
> > * I'm sure there are other new features, but this is all that comes to
> >mind at the moment.
>
> there was some issues with efficiency of darcs 1.x. am i correctly
> understoo
On Apr 7, 2008, at 14:28 , Bulat Ziganshin wrote:
Hello David,
Monday, April 7, 2008, 9:22:25 PM, you wrote:
* I'm sure there are other new features, but this is all that
comes to
mind at the moment.
there was some issues with efficiency of darcs 1.x. am i correctly
understood that th
On Apr 7, 2008, at 12:12 , PR Stanley wrote:
Hi
data Bool = False | True
deriving (Eq, Or, Show, Read)
Bool is an instance of Eq, Ord, Show and Read. It is derived form
these classes. If that is the meaning of the keyword deriving then
wouldn't a different keyword such as from or derivati
Hello David,
Monday, April 7, 2008, 9:22:25 PM, you wrote:
> * I'm sure there are other new features, but this is all that comes to
>mind at the moment.
there was some issues with efficiency of darcs 1.x. am i correctly
understood that these issues was not addressed by new release?
its har
> Hi
> data Bool = False | True
> deriving (Eq, Or, Show, Read)
>
> Bool is an instance of Eq, Ord, Show and Read. It is derived form
> these classes.
No. "deriving ..." here does not mean that Bool is derived from those
classes; it's not a statement about inheritance or anything similar.
"
Hi,
I would like to try HXT, but I can't manage to build it. I resolved all
the dependencies, but I get the following error:
> > [EMAIL PROTECTED]:~/Desktop/hxt$ make all
> > make -C src all VERSION=7.5
> > make[1]: Entering directory `/home/ln/Desktop/hxt/src'
> > make install_local_hxt
>
Hello darcs users,
I am pleased to announce the release of darcs 2.0.0! It's been a long time
coming, and hopefully you will be pleased with the result. Notable new
features include (in no particular order):
* New ssh-connnection mode that dramatically improves connection times
when darcs 2.
Paul,
> Hi
> data Bool = False | True
> deriving (Eq, Or, Show, Read)
>
> Bool is an instance of Eq, Ord, Show and Read. It is derived form
> these classes.
No. "deriving ..." here does not mean that Bool is derived from those
classes; it's not a statement about inheritance or anything simil
Hi
data Bool = False | True
deriving (Eq, Or, Show, Read)
Bool is an instance of Eq, Ord, Show and Read. It is derived form
these classes. If that is the meaning of the keyword deriving then
wouldn't a different keyword such as from or derivative or even
derivation be closer to the semantics
On Mon, 7 Apr 2008, Mark P Jones wrote:
The surprising thing about this example is the fact that
the definition of foo is accepted, and not the fact that
the definition of foo' is rejected. At least in Manuel's
"equivalent" program using functional dependencies, both
functions have ambiguous ty
Hi,
2008/4/7 Paul Keir <[EMAIL PROTECTED]>:
> I'm using buildExpressionParser, and I'd like to use alphanumeric operator
> characters. I get an (unexpected "a") error though. With a test string like
> "-a" if "a" is used in any of the "reservedOpNames". I'm aiming for the
> Fortran operators like
I'm not getting it. Are you thinking that Bool itself "is derived form
these classes", rather than those four instances for Bool? - Conal
On Mon, Apr 7, 2008 at 9:12 AM, PR Stanley <[EMAIL PROTECTED]> wrote:
> Hi
> data Bool = False | True
> deriving (Eq, Or, Show, Read)
>
> Bool is an instanc
Hi
data Bool = False | True
deriving (Eq, Or, Show, Read)
Bool is an instance of Eq, Ord, Show and Read. It is derived form
these classes. If that is the meaning of the keyword deriving then
wouldn't a different keyword such as from or derivative or even
derivation be closer to the semantics
Hi,
I'm using buildExpressionParser, and I'd like to use alphanumeric
operator characters. I get an (unexpected "a") error though. With a test
string like "-a" if "a" is used in any of the "reservedOpNames". I'm
aiming for the Fortran operators like ".and.".
The listing below may be helpful
Ian Lynagh wrote:
Fellow Haskellers,
We (Björn Bringert, Duncan Coutts and Ian Lynagh) are pleased to
announce that we have recently set up a Haskell consultancy company,
Well-Typed LLP (http://www.well-typed.com/).
Congratulations!
Do you have a plan to market your services to people who mig
On Mon, Apr 7, 2008 at 4:11 PM, Thomas Schilling
<[EMAIL PROTECTED]> wrote:
> It doesn't have to be perfect. Make sure you know how to use monad
> transformers. Also take a look at tag soup and the various HTML/XML
> parsers. I'm sure there's plenty to work on.
>
> My guess would be, tha
Thanks. reservedOp is a better fit; ":+" should only be ":+".
I also overcame my type issues in an ad-hoc manner, adding
>> return ()
whenever I needed to.
-Original Message-
From: Tillmann Rendel [mailto:[EMAIL PROTECTED]
Sent: 30 March 2008 12:30
To: Paul Keir; haskell-cafe@haskell.o
On Mon, Apr 07, 2008 at 04:52:51AM -0700, John Meacham wrote:
> On Mon, Apr 07, 2008 at 04:45:31AM -0700, David Roundy wrote:
> > I wonder about the efficiency of this implementation. It seems that for
> > most uses the result is that the size of a Nat n is O(n), which means that
> > in practice y
Hi,
Am Freitag, den 04.04.2008, 22:44 +0100 schrieb Neil Mitchell:
> Hi
>
> > We can however write function like this:
> >
> > eqLengths [] [] = True
> > eqLengths (x:xs) (y:ys) = eqLengths ys xs
> > eqLengths _ _ = False
> >
> > which looks just fine for me.
>
> I have this defined functio
The surprising thing about this example is the fact that
the definition of foo is accepted, and not the fact that
the definition of foo' is rejected. At least in Manuel's
"equivalent" program using functional dependencies, both
functions have ambiguous types, and hence both would be
rejected. It
On 7 apr 2008, at 15.36, Yitzchak Gale wrote:
Max Desyatov wrote:
I'm interested in working on a library for a stateful web
browsing in
Haskell during Google Summer of Code.
Thomas Schilling wrote:
Also, for a GSoC proposal you should try to convince the mentors,
why your
project is use
On Mon, Apr 7, 2008 at 4:16 PM, Yitzchak Gale <[EMAIL PROTECTED]> wrote:
> You didn't show us the code for countForPoints. I'll bet you wrote
> something like
>
> countForPoints area ls count points =
> sum $ map (countPathsFrom area (count + 1) ls) points
>
> Unfortunately, the standard sum
Max Desyatov wrote:
>> I'm interested in working on a library for a stateful web browsing in
>> Haskell during Google Summer of Code.
Thomas Schilling wrote:
> Also, for a GSoC proposal you should try to convince the mentors, why your
> project is useful for Haskell in general. So maybe you have
class Enum a where
...
-- | Used in Haskell's translation of [n,n'..m].
enumFromThenTo :: a -> a -> a -> [a]
So [x, y .. z] becomes "enumFromThenTo x y z".
Each instance of Enum is free to implement enumFromThenTo and friends
in any way it likes.
So with Ints you have [1, 3 .. 10] :: [Int]
Alexander Kireyev wrote:
> While trying to write a program for the countPaths Code Jam problem I
> ran into what seems to me as a weird behaviour in terms of memory
> allocation...
> The profiling log (./paths +RTS -P) shows the following time/space
> behaviour for them...
Hi Alexander,
I'm
On 7 apr 2008, at 14.46, Max Desyatov wrote:
Hi,
I'm interested in working on a library for a stateful web browsing in
Haskell during Google Summer of Code. The basic idea is described at
http://hackage.haskell.org/trac/summer-of-code/ticket/1107.
WWW::Mechanize is a ready to use library wri
Hi,
I'm interested in working on a library for a stateful web browsing in
Haskell during Google Summer of Code. The basic idea is described at
http://hackage.haskell.org/trac/summer-of-code/ticket/1107.
WWW::Mechanize is a ready to use library written in Perl, though I
used python's mechanize wh
Uwe Schmidt wrote:
> Lieber Herr Hübel,
> lieber Herr Schlatt,
sorry for spamming haskell-cafe
Uwe
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On 2008-04-04, Neil Mitchell <[EMAIL PROTECTED]> wrote:
>> What do you mean by "proper Lazy naturals"? Peano ones?
>
> Yes
Not _strictly_ necessary. And I'd definitely like some suitable
typeclass put in place. This represents positive arithmetic with
a list homomorphism that forgets the elemen
On Sun, 06 Apr 2008 14:07:22 +0200, wrote:
> Hello,
>
> we are pleased to announce the first beta release of Hayoo!, a Haskell
> API
> search engine providing advanced features like suggestions,
> find-as-you-type,
> fuzzy queries and much more.
>
> Visit Hayoo! here: http://holumbus.fh-wedel.de
At 12:28 07/04/2008, you wrote:
On Fri, Apr 4, 2008 at 10:49 PM, Andrew Coppin
<[EMAIL PROTECTED]> wrote:
> More to the point, the range y..z goes in steps of y-z. ;-)
[x,y..z] goes in steps of y-x ;-), [y..z] goes in steps of 1
(depending on the type).
Could you elaborate please?
On Mon, Apr 07, 2008 at 04:45:31AM -0700, David Roundy wrote:
> I wonder about the efficiency of this implementation. It seems that for
> most uses the result is that the size of a Nat n is O(n), which means that
> in practice you probably can't use it for large numbers.
>
> e.g. it seems like
>
Lieber Herr Hübel,
lieber Herr Schlatt,
ich habe gerade das Announcement von Holumbus
in haskell.org gelesen und natürlich auch Holumbus ausprobiert.
RICHTIG GUT!
Viele Gruesse
Uwe Schmidt
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On Sun, Apr 06, 2008 at 07:12:24AM -0700, John Meacham wrote:
> On Fri, Apr 04, 2008 at 04:46:22PM +0100, Neil Mitchell wrote:
> > Where length xs = 1 and ys = 1000. This takes 1000 steps to tell the
> > Int's aren't equal, since we don't have proper lazy naturals. If we
> > did, it would take 2 st
On 2008-04-03, Chris Smith <[EMAIL PROTECTED]> wrote:
> Hans Aberg wrote:
>> This problem is not caused by defining f+g, but by defining numerals as
>> constants.
>
> Yup. So the current (Num thing) is basically:
>
> 1. The type thing is a ring
> 2. ... with signs and absolute values
> 3. ... alon
On Fri, Apr 4, 2008 at 10:49 PM, Andrew Coppin
<[EMAIL PROTECTED]> wrote:
> More to the point, the range y..z goes in steps of y-z. ;-)
[x,y..z] goes in steps of y-x ;-), [y..z] goes in steps of 1
(depending on the type).
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Ha
Hello,
While trying to write a program for the countPaths Code Jam problem I
ran into what seems to me as a weird behaviour in terms of memory
allocation.
The task is to count the number of way you can spell a certain "word"
by walking some path on a board of letters.
Being a newbie I started wi
type instance Id Int = Int
foo :: Id a -> Id a
foo = id
foo' :: Id a -> Id a
foo' = foo
Is this expected?
Yes, unfortunately, this is expected, although it is very unintuitive.
This is for the following reason.
Huh? This sounds very wrong to me, simply because foo and foo' have the
ve
Manuel M T Chakravarty wrote:
Ganesh Sittampalam:
The following program doesn't compile in latest GHC HEAD, although it
does if I remove the signature on foo'.
{-# LANGUAGE TypeFamilies #-}
module Test7 where
type family Id a
type instance Id Int = Int
foo :: Id a -> Id a
foo = id
foo' ::
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