John,
If I use zippers, do all my nodes need to be the same type?
No, zippers can also be defined for mutually recursive data types. In
a paper to be presented at ICFP, next September, Alexey Rodriguez,
Andres Löh, Johan Jeuring, and I show how zippers for mutually
recursive data types
On Wed, Jul 15, 2009 at 3:02 AM, Thomas Hartmantphya...@gmail.com wrote:
Please suggest more of these types of exercises if you have them and
maybe we can collect the folk wisdom into a wiki page and/or exercise
page for beginners.
My 'stream' library[1] also has some examples. Look at the
On Tue, Jul 14, 2009 at 11:27 PM, Lyle Kopnickyli...@qseep.net wrote:
If I am running GHC on 64-bit Windows, do I have a choice of building a
32-bit or 64-bit app? On a cursory glance through the command-line options,
I didn't find anything.
I don't think there are cross-compiling version of
Hi,
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
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山高哪阻野云飞
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2009/7/15 Magicloud Magiclouds magicloud.magiclo...@gmail.com:
Hi,
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
++ is a function; you can't pattern-match on that.
Cheers,
Thu
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2009/7/15 minh thu not...@gmail.com:
2009/7/15 Magicloud Magiclouds magicloud.magiclo...@gmail.com:
Hi,
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
++ is a function; you can't pattern-match on that.
But here you can match against
Technically, the reason is not that (++) is a function, but that it is
not a constructor of the [] type.
And, not only is it not a constructor, but it also *can't* be one,
because the main characteristic of pattern matching in Haskell is that
it is (contrary to Prolog's unification) unambiguous
On 15 Jul 2009, at 12:25, Eugene Kirpichov wrote:
If ++ could be pattern matched, what should have been the result of
let (x++y)=[1,2,3] in (x,y)?
It will branch. In terms of unification, you get a list of
substitutions.
Hans
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Hi again!
We have decided to delay the release cycle slightly for 2.3 and release another
beta. The primary reason for this is our Windows support -- I would like to
invite all Windows users to install darcs-beta and give it a ride. If you have
a working cabal-install, all you need to do is run:
On Wed, Jul 15, 2009 at 3:08 AM, Hans Aberg hab...@math.su.se wrote:
On 15 Jul 2009, at 12:25, Eugene Kirpichov wrote:
If ++ could be pattern matched, what should have been the result of
let (x++y)=[1,2,3] in (x,y)?
It will branch. In terms of unification, you get a list of substitutions.
Err, technically, aren't functions and constructors mutually exclusive? So
if something is a function, it's, by definition, not a constructor?
On Wed, Jul 15, 2009 at 6:25 AM, Eugene Kirpichov ekirpic...@gmail.comwrote:
Technically, the reason is not that (++) is a function, but that it is
not
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
On 15 Jul 2009, at 13:22, Luke Palmer wrote:
If ++ could be pattern matched, what should have been the result of
let (x++y)=[1,2,3] in (x,y)?
It will branch. In terms of unification, you get a list of
substitutions.
f :: [a] - ([a],[a])
f (x ++ y) = (x,y)
For an argument s, any pair (x,
On Wed, Jul 15, 2009 at 08:09:37AM -0400, Andrew Wagner wrote:
Err, technically, aren't functions and constructors mutually exclusive? So
if something is a function, it's, by definition, not a constructor?
I guess what Eugene Kirpichov meant was that not being a function
(and being a
Actually, you can make a joinInner for the State monad. However, it
does not allow the inner function (h) to change the state, because how
state is threaded through a monad N is different for each N.
i :: (Monad n) = (a - State s b) - (b - n c) - (c - State s d) -
(a - State s (n d))
i f
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
Maybe a small abstract can help, as I once also got
confused by that.
* First, syntax without operators
You can only match on constructors. So, if
you have
data Test = Test1
After my colleague explained me about zippers and how one could derive the
datatype using differential rules, I had to read about it.
So I started reading
http://en.wikibooks.org/wiki/Haskell/Zippers#Mechanical_Differentiation
This page contains the sentence: *For a systematic construction, we
On Tue, Jul 14, 2009 at 6:02 PM, Thomas Hartmantphya...@gmail.com wrote:
myiterate f x =
let nxt = f x
in nxt `seq` x : myiterate f nxt
iterate' f x = x `seq` x : iterate' f (f x)
seems better; it doesn't evaluate list elements you don't visit.
let test = 1 : 2 : 3 : undefined in last $
Hi,
as pointed out in this list, it seems that a tying the knot example
would be the one better explaining the power of Haskell's
lazy-by-default approach against Python+Iterator's approach to
laziness.
So, in these days I'm trying to grasp the meaning of this tying the
knot concept which seems
doesn't make much sense to me yet, although I suspect I can read the mu as a
lambda on types?
Not really. The mu has more to do with recursion.
Matthias.
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And the urls:
home - http://hackage.haskell.org/package/shelltestrunner
darcs repo - http://joyful.com/repos/shelltestrunner
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(and, the original which I didn't cc to -cafe.)
I'm pleased to announce the first release of shelltestrunner: a small
tool for testing any command-line program by running it through
shell tests defined with a simple file format. Each test can specify
the command-line arguments, input,
Matthias Görgens matthias.goerg...@googlemail.com writes:
doesn't make much sense to me yet, although I suspect I can read the mu as a
lambda on types?
Not really. The mu has more to do with recursion.
I'd say it's entirely to do with recursion. It's like the Y combinator
(or fix) for
On Wed, Jul 15, 2009 at 7:33 PM, Cristiano
Pariscristiano.pa...@gmail.com wrote:
fib = 1:1:fib `plus` (tail fib) where plus = zipWith (+)
Of course, this was something I already encountered when exploring the
Y-combinator. Anyhow, I tried to translate this implementation to
Python using
Hello,
I have just a very vague understanding of what homomorphic encryption is,
but I was wondering if homomorphic encryption behaves as a one-way monad
(like IO).
So for example, suppose you wrote a function that worked on encrypted email
to determine if it spam, maybe it looks like this:
Hi all
I recently used 2 hours of work looking for a bug that was causing
Program error: Prelude.!!: index too large
This is not very informative. It did not give me a hint which function
was causing this. In C adding a few printf would have helped me, but
in haskell I was not sure how to do
fernanbolando:
Hi all
I recently used 2 hours of work looking for a bug that was causing
Program error: Prelude.!!: index too large
This is not very informative. It did not give me a hint which function
was causing this. In C adding a few printf would have helped me, but
in haskell I
On Wed, Jul 15, 2009 at 11:54 PM, Jason Dagitda...@codersbase.com wrote:
Hello,
I have just a very vague understanding of what homomorphic encryption is,
but I was wondering if homomorphic encryption behaves as a one-way monad
(like IO).
An interesting idea. Let's see where this leads.
I
A new generator package has been uploaded to Hackage.
It implements an alternative list monad transformer, a list class, and
related functions.
The difference from mtl/transformers's ListT is that
mtl is a monadic action that returns a list:
newtype ListT m a = ListT { runListT :: m [a] }
Of course !! is only one cause for this kind of errror. Another is
ghci head []
*** Exception: Prelude.head: empty list
Unfortunately this kind of bug is very hard to debug due to the lazy
nature of haskell. You don't have a stack trace as in Java, PHP, ..
Example:
data D = D String
a,b ::
I think there may be a problem here.
Homomorphic encryption is a form of encryption where one can perform a
specific algebraic operation on the plaintext by performing a (possibly
different) algebraic operation on the ciphertext.
The word specific means that the functor is discrete, not
Fernan Bolando wrote:
Program error: Prelude.!!: index too large
This is not very informative. It did not give me a hint which function
was causing this.
In addition to the debugging methods that have been mentioned, the
Safe library provides a way to write the code more robustly and/or
If M is a monad transformer (e.g. StateT) and able to be parameterised
over an arbitrary monad, you can do something related, which may
actually be more useful to you.
Given the definition of StateT from mtl:
newtype StateT s m a = StateT {
runStateT :: s - m (a, s)
}
you could define this
#def inline int signof(int x) {return x0?-1:x0?1:0;}
foreign import ccall safe
signof :: CInt - CInt
Is it possible to get that #def as a result of
a macro? Say, something like this:
---
(WARNING: invalid code)
#define ret(name,value,type) \
#def inline type name (void) {return value;}
On Jul 15, 2009, at 5:25 PM, Benjamin L.Russell wrote:
it interesting that you should use the biological term disease;
according to a post [1] entitled Re: Re: Smalltalk Data Structures
and Algorithms, by K. K. Subramaniam, dated Mon, 29 Jun 2009
11:25:34 +0530, on the squeak-beginners mailing
On Jul 15, 2009, at 9:59 PM, minh thu wrote:
2009/7/15 Magicloud Magiclouds magicloud.magiclo...@gmail.com:
Hi,
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
++ is a function; you can't pattern-match on that.
Doesn't matter, it's not
On Jul 15, 2009, at 9:57 PM, Magicloud Magiclouds wrote:
Hi,
I do not notice this before. fun ([0, 1] ++ xs) = .. in my code
could not be compiled, parse error.
I apologise to everyone for my previous message in this
thread. There was a Haskell message in amongst some Erlang
messages, and
On Wed, Jul 15, 2009 at 2:18 PM, Max Rabkinmax.rab...@gmail.com wrote:
On Wed, Jul 15, 2009 at 7:33 PM, Cristiano
Pariscristiano.pa...@gmail.com wrote:
fib = 1:1:fib `plus` (tail fib) where plus = zipWith (+)
...
...
This indicates that you think tying the knot should be impossible in
Robert Greayer wrote:
Isn't tying the knot (in the way 'fib' does) straightforward with closures
a la Python/Ruby/Smalltalk (without mutation)?
Even in a syntactically clumsy language like Java, a
tying-the-knot implementation equivalent to the canonical Haskell one is
not difficult, e.g.
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