On 2/26/07, Thomas Hartman [EMAIL PROTECTED] wrote:
Here's my, probably very obvious, contribution.
What I'd like feedback on is
1) code seem ok? (hope so!)
Hi Thomas,
tail [] raises an error, therefore your code will fail when n length xs (
e.g. mydrop 3 [1,2] will raise an exception,
On 2/26/07, Chris Eidhof [EMAIL PROTECTED] wrote:
Hey everyone,
we added some examples to this page. There are some topics that don't
have any examples, notably:
# 11 Network Programming
# 12 XML
* 12.1 Parsing XML
# 13 Databases
* 13.1 MySQL
* 13.2 PostgreSQL
* 13.3 SQLite
I'd heard of quick check, but haven't got my head around it. This
seems like a good place to start.
I understand you have to build an invariant and then you can automate
against it, eg reverse of reverse is your original string
prop_RevRev xs = reverse (reverse xs) == xs
where types = xs::[Int]
Hello Tim,
Monday, February 26, 2007, 2:26:44 AM, you wrote:
Rather than using existential types, a simple record of
functions can be often be useful. ie:
data Component = Component {
draw :: String
add :: Component - Component
}
Steve, you can look at the pages
Stefan O'Rear wrote:
How do I get my original function back which just turns a standard
list to one of the funky lists, or is that just impossible with
GADT's? Do I now have to wrap all the fuctions I use, i.e. pass
safeMap in CPS?
AFAIK you can't. Fortunately the CPS transform can be very
Just a quick note to say that the Haskell implementation shootout is
progressing, now supporting jhc, fixing a range of bugs, and providing
more benchmark programs. Nice average numbers are also reported for the
relative performance of each compiler or interpreter.
On x86:
ndmitchell:
Hi
And also I guess the compilers will do more optimisations, etc.
So this suggests an obvious extra feature for nobench which would be the
ability to view a graph of each compiler's performance over a period of
time, obviously this probably wouldn't be useful for at least a few
On Sat, Feb 24, 2007 at 12:47:19PM +0100, Henk-Jan van Tuyl wrote:
Is this something for the list at
http://haskell.org/mailman/listinfo
That's generated by mailman, and as far as I know can't be easily
altered.
(Maybe this page could be moved to haskellwiki?)
Perhaps adding a list of
On Sun, Feb 25, 2007 at 10:40:13PM +, Neil Mitchell wrote:
data ConsT a
data NilT
data List a t where
Cons :: a - List a b - List a (ConsT b)
Nil :: List a NilT
...
Defining safeMap was trivial, but one thing I couldn't figure out was
how to write something like fromList:
According to
http://www.cs.chalmers.se/~rjmh/QuickCheck/
Quickcheck is distributed with ghc.
I seem to recall this came with ghc 6.4. After upgrading to ghc 6.6,
however, I don't seem to have it anymore.
Do I need to install it from cabal? If so, I assume this would start
by wgetting
I am really curious about this style of programming, and find myself
playing with it from time to time.
The example so far is very nice, but the funniest part is missing.
That is, defining appendL.
appendL :: List a t1 - List a t2 - List a t3
This says that the append of a list of length
David Roundy droundy at darcs.net writes:
My latest attemp (which won't compile with the HEAD ghc that I just compiled,
probably because I haven't figured out the synatax for guards with indexed
types is:
class WitnessMonad m where
type W m :: * - * - *
(=) :: (WitnessMonad m',
On Sun, 25 Feb 2007, Peng Zhang wrote:
Hi folks,
My primary language is R, which is an imperative functional language. I
start to learn haskell and try to use it instead when a project is
time-consuming and it takes months in R. I like the language very much
so far, but I do miss some
On 26/02/07, Thomas Hartman [EMAIL PROTECTED] wrote:
According to
http://www.cs.chalmers.se/~rjmh/QuickCheck/
Quickcheck is distributed with ghc.
I seem to recall this came with ghc 6.4. After upgrading to ghc 6.6,
however, I don't seem to have it anymore.
Hmm, which release do you have? I
Thomas Hartman wrote:
According to
http://www.cs.chalmers.se/~rjmh/QuickCheck/
Quickcheck is distributed with ghc.
I seem to recall this came with ghc 6.4. After upgrading to ghc 6.6,
however, I don't seem to have it anymore.
Do I need to install it from cabal? If so, I assume this would
On Mon, Feb 26, 2007 at 04:35:06PM +0100, Pepe Iborra wrote:
First, via existentials:
appendL1 :: List a t1 - List a t2 - exists t3. List a t3
It seems like this problem is begging for the new indexed types (for which
I never remember the right syntax).
type AddListTs :: * - * - *
AddListTs
I'm brand new to haskell and I'm having trouble using classes. The basic idea
is I want two classes, Sine and MetaSine, that are both instances of ISine.
This way I can use the act method and recurse through the metasines and sines.
Here's my code:
module Main
where
class ISine a where
L.S.,
Links in the Haskell code in the wiki pages point to wrong labels; for
example, if 'print' is used, it is linked to:
http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:print
the colon should be %3A:
[redirecting to haskell-cafe, since this is getting to be a long discussion]
On 2/26/07, Andrzej Jaworski [EMAIL PROTECTED] wrote:
The examples I pointed to seem to share strong and relatively consistent
logic of a program. In case of large GA (e.g. Royal Road Problem) and IFP
(e.g. ADATE) SML
... and now I have more questions. Maybe it would be better if I just
asked them on the mailing list, and then incorporated the answers into
the wiki myself.
Question #1 is compiling FFI using modules. I'd like to use ghc
--make for the speed and convenience, but obviously it doesn't know
how
All record fields are in the same namespace, and furthermore this is
also the same namespace of functions and class methods. In other words
you cannot have two record types containing the same field name, and you
cannot have a record field and a function using the same name, and you
cannot
On 2/26/07, Thomas Nelson [EMAIL PROTECTED] wrote:
I'm brand new to haskell and I'm having trouble using classes. The basic idea
is I want two classes, Sine and MetaSine, that are both instances of ISine.
'class' in Haskell doesn't mean the same as 'class' in C++ or Java. I
found it easier at
Hello,
I know StateT is exactly aimed at dealing with a state and an inner
monad but I have an example in which I have to mix State and IO and in
which I didn't get to an elegant solution using StateT.
I have a higher order function which gets some State processing
functions as input, makes
On Mon, Feb 26, 2007 at 04:35:06PM +0100, Pepe Iborra wrote:
I am really curious about this style of programming, and find myself
playing with it from time to time.
The example so far is very nice, but the funniest part is missing.
That is, defining appendL.
appendL :: List a t1 - List
On 2/26/07, Alfonso Acosta [EMAIL PROTECTED] wrote:
The returned type is a StateT and the only way in which I succesfully
managed to internally work with both State and StateT is converting
from the former to the later one using this function (not elegant at
all)
I may be missing something,
On 2/27/07, Kirsten Chevalier [EMAIL PROTECTED] wrote:
I may be missing something, but why are you using both State and
StateT? Maybe I don't understand your code, but it seems like you
could be using StateT everywhere you're currently using State.
Well, as far as I know using StateT s IO a
On Mon, Feb 26, 2007 at 01:02:57PM -0800, Evan Laforge wrote:
Question #1 is compiling FFI using modules. I'd like to use ghc
--make for the speed and convenience, but obviously it doesn't know
how to compile the C. So my hybrid approach has been to write a
makefile for the C, and then make
On 2/26/07, Alfonso Acosta [EMAIL PROTECTED] wrote:
On 2/27/07, Kirsten Chevalier [EMAIL PROTECTED] wrote:
I may be missing something, but why are you using both State and
StateT? Maybe I don't understand your code, but it seems like you
could be using StateT everywhere you're currently
On 2/27/07, Kirsten Chevalier [EMAIL PROTECTED] wrote:
So what if you changed your netlist function so that the type
sig would be:
netlist :: DT.Traversable f =
(State s (S HDPrimSignal) - State s v ) - -- new
(State s (Type,v) - S v - State s ()) - -- define
interesting. it leads to something that feels much more like an object
based, as opposed to a class based, system.
as far as haskell is concerned, everything has the same type, even
though different instances have very different behavior.
instance variables are captured by the closures that
in addition, a good example of how to apply quickcheck would be really awesome.
without using the standard drop g
On 2/26/07, Thomas Hartman [EMAIL PROTECTED] wrote:
Here's my, probably very obvious, contribution.
What I'd like feedback on is
1) code seem ok? (hope so!)
2) What do you think
ok maybe i should have read ahead. but still, i can see how to apply
hunit, but not quickcheck. but quickcheck seems more powerful.
On 2/26/07, Steve Downey [EMAIL PROTECTED] wrote:
in addition, a good example of how to apply quickcheck would be really
awesome.
without using the standard drop g
I want to write a class introducing a function which should append a b
resulting in a HList containing a and b (order doesn't matter)
So I came up with:
= code ===
class (HList c) = HListAppendArbitrary a b c | a b - c where
Marc Weber wrote:
class (HList c) = HListAppendArbitrary a b c | a b - c where
hAppendArbitrary :: a - b - c
-- instance HList + HList (1)
instance (HList a, HList b, HAppend a b c, HList c)
= HListAppendArbitrary a b c where
hAppendArbitrary a b = hAppend a b
--
Lennart wrote:
OOHaskell is ingenious, but it's a terrible way to use Haskell.
It's very unidiomatic Haskell, and it makes you do things in the
same old OO way.
It's probably obvious but let me say that ...
OOHaskell is more of a proof of concept and a sandbox for OO language design.
It is
Stefan O'Rear wrote:
Personally I like the GADT approach best since it is very flexible and
convienient. I have never used a purpose-build computer proof system,
but (modulo _|_) it took me less than 10 minutes to answer
LoganCapaldo (on #haskell)'s challenge to proof that + was commutative
Wow.
That said, it is quite possible in Haskell to achieve genuine
class-based dispatch, with backtracking if necessary:
http://pobox.com/~oleg/ftp/Haskell/poly2.txt
Thanks for digging this up.
I'll have to reread it tomorrow.
I wasn't able to find the definition of AllOf(But):
quote
Steve Downey wrote:
In the last OO design in Haskell thread (and probably in every one
preceeding it), it was suggested that having some examples might be a good
idea.
Since most people with existing designs will have some familiarity with
Design Patterns, and those are typical building
G'day all.
Quoting Aaron McDaid [EMAIL PROTECTED]:
'class' in Haskell doesn't mean the same as 'class' in C++ or Java. I
found it easier at first to thing of them as:
A Haskell 'class' is more like a Java interface.
Haskell types are more like what you might think of as 'class'es.
Hi folks
in C and C++ world the humble comma is an operator. Is this also the
case in Haskell or, is it classed as a function?
In the wikibook they talk about consing new elements onto a list.
Does this cons stand for anything meaningful in the English language?
For example, is it short for
G'day all.
Oh, one more thing.
Quoting Aaron McDaid [EMAIL PROTECTED]:
Somebody more knowledgeable can describe the etymology of the terms,
[...]
You can think of a type as a set of values. For example, Bool is the
set { False, True }. A class, then, is a set of types.
The distinction
I just started reading Haskell's overlooked object system.
http://www.cwi.nl/%7Eralf/OOHaskell/
The survey of existing object encodings looks like a good place to start,
although for several, where Either is used as a union type there are some
rather obvious scaling problems. g
If I've
On Mon, 26 Feb 2007 17:28:59 -0800 (PST)
[EMAIL PROTECTED] wrote:
The problem with GADTs and other run-time based evidence is just
that: _run-time_ based evidence and pattern-matching. In a non-strict
system, checking that the evidence is really present is the problem on
and of itself.
P. R. Stanley wrote:
You know, as soon as I posted the message I remembered the destructive
assignment thingummy. the following is what I was talking about:
Prelude 13:[1, 2]
[13, 1, 2]
which I don't believe has an address in the memory, correct?
No. It does have a well-defined address in
On 2/26/07, Dan Weston [EMAIL PROTECTED] wrote:
P. R. Stanley wrote:
In C, for example, iteration could be implemented using the if construct
with the dreaded goto command. So, strictly speaking, the while loop
could be classed as syntax sugar. Yet, the while loop is a
well-recognized
On Feb 26, 2007, at 22:17 , P. R. Stanley wrote:
Prelude 13:[1, 2]
[13, 1, 2]
which I don't believe has an address in the memory, correct?
If I understand what you're getting at: internally it just allocates
a new cons cell, stuffs 13 in the left side and a pointer to the
existing list
On 2/26/07, P. R. Stanley [EMAIL PROTECTED] wrote:
Back to the comma, surely, syntax sugar fulfills the role of an
operator, a function, or a sequence of low-level procedures, either
in part or comprehensively.
In C, for example, iteration could be implemented using the if
construct with the
Hi.
I've got stuck with the following compilation error I probably can't fully
understand:
--
Building library...
...
Using package config file: /usr/local/lib/ghc-6.6/package.conf
wired-in package base mapped to base-2.0
Steve Downey wrote:
interesting. it leads to something that feels much more like an object
based, as opposed to a class based, system.
as far as haskell is concerned, everything has the same type, even
though different instances have very different behavior.
the question is, which plays
Thank you all for your advice so far. I went back and tried to simplify
my code, but I'm still stuck. The basic idea I want is something like an
arbitrary tree structure, where MetaSines are the branches containing
Sines, and Sines are the leaves containing strings. I want to recurse
Pepe Iborra:
David Roundy droundy at darcs.net writes:
My latest attemp (which won't compile with the HEAD ghc that I just
compiled,
probably because I haven't figured out the synatax for guards with indexed
types is:
class WitnessMonad m where
type W m :: * - * - *
(=)
On Mon, 26 Feb 2007 23:41:14 -0600 (CST), you wrote:
Here's my second attempt at the code:
...
You've left out a bunch of constructors, and there are various other
errors here and there. I think this will do what you want:
data ISine =
Sine Integer Integer Integer [Char] |
MetaSine
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