comp.lang.haskell Google Group

Re: Transparent results cache

mark.carr...@aetion.com (Mark T. B. Carroll) — Fri, 20 Лис 2009 22:23:42 UT

Huh, yes, I seem good at reinventing wheels. (The lessons stick with me
better that way though!) Thank you. Some of that code looks rather familiar!
Mmm. I'm hoping that it doesn't become enough of a problem that I have
to try to put together a simple test case that evinces the bug.
Mark

Re: Transparent results cache

dan.d...@gmail.com (Dan Doel) — Fri, 20 Лис 2009 22:13:34 UT

You may be interested in this paper:
[link]
And, I do think you probably want NOINLINE on the call of cached (otherwise
the call may be inlined, and you may end up with multiple separately
memoized functions), but I'm not 100% sure. I'm not sure why that'd be

Re: Transparent results cache

mark.carr...@aetion.com (Mark T. B. Carroll) — Fri, 20 Лис 2009 16:14:36 UT

I did indeed grow doubtful about where I'd put it and have tried moving
it around and thinking about it more.
Still, now I'm getting the occasional segmentation fault from my code.
I'm not knowingly using threading or concurrency, unless
Control.Parallel.Strategies.rn f does it behind the scenes in a way that

Transparent results cache

mark.carr...@aetion.com (Mark T. B. Carroll) — Wed, 18 Лис 2009 18:29:07 UT

I wrote something that is possibly a bit horrifying. I seem to have got
away with it for now. I don't normally use things like unsafePerformIO
but it occurred to me that I could write a kind of transparent results
cache for functions. I'd certainly be interested in comments about how
I screwed it up or shouldn't even be thinking such awful things. At

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Re: happs coming alone?

mark.carr...@aetion.com (Mark T. B. Carroll) — Fri, 30 Жов 2009 17:09:12 UT

It's not something I've had to know about. I remember some talk of a
fork - see [link] - but I have no experience with either.
Also, for dynamic sites,
[link] may be useful.
Mark

Re: happs coming alone?

gavcom...@gmail.com (gavino) — Fri, 30 Жов 2009 05:21:50 UT

coming along I meant
nice youtube vid by the way
how about some demo sites?
something like a mock craigslist or digg would be cool

happs coming alone?

gavcom...@gmail.com (gavino) — Fri, 30 Жов 2009 04:51:35 UT

see this? [link] lisp has a nice webserver

Re: monads for lambda calculus

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Wed, 21 Жов 2009 07:57:24 UT

Exactly. Though in don't see what the latter has to do with the former :-)
If you haven't done already, I recommend reading up on F-Algebras.
Exactly. It's superficial, it's unnatural, it doesn't fit the intended
use. So why insist on it?
In general, they don't necessarily exist. If you look at it categorically,

Re: monads for lambda calculus

jon.gallagher...@gmail.com (jon.gallagher.04) — Wed, 21 Жов 2009 07:13:34 UT

Right, that's the point of data in the lambda calculus. Inductive
data types are there own folds. So that
nil = \nc.n
cons a l = \nc. c a (l n c) <=>
cons = \al.\nc.c a (l n c)
Then
fold v f l = l v f <=>
fold = \vfl.lvf
And
map f l = fold nil (\a m. cons (f a) m) l <=>
map = \f l . fold nil (\am.cons (f a) m) l

Re: monads for lambda calculus

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Tue, 20 Жов 2009 21:59:40 UT

BTW, if you define the representation this way, a nice test case is
(\x.x x)(\x.x x). If that doesn't work like it should, you need to improve
the alpha-conversion handling :-)
BTW, one can define fold and (f)map for every covariant ADT, so that's
in no way special to Lambda. Though I think it's a bit roundabout to

monads for lambda calculus

jon.gallagher...@gmail.com (jon.gallagher.04) — Tue, 20 Жов 2009 05:04:28 UT

Greetings Comp.Lang.Haskell Community,
I have a program that serves a lambda calculus reducer, but I want to
play with it and see what various class representations give, such as
functors and monads.
So consider
Then, of course fold,
So that we can give an instance of functor,
Next we can try to write an instance of monads. We have an obvious

* extended deadline: FLOPS 2010: Last Call for Papers *

matthias.bl...@gmail.com (Matthias) — Tue, 20 Жов 2009 02:42:40 UT

------------------------------ ------------------------------ ----------------
LAST CALL FOR PAPERS
Tenth International Symposium on Functional and Logic Programming
(FLOPS 2010)
April 19-21, 2010
Sendai, Japan
[link]
** EXTENDED SUBMISSION DEADLINES **

Re: Just beginning problem

mark.carr...@aetion.com (Mark T. B. Carroll) — Mon, 19 Жов 2009 20:22:30 UT

For instance, seeing intersectBy, etc., I was just wondering aloud where
differenceBy is, only for it to be pointed out to me that it's
deleteFirstsBy. (In my defense, Hayoo was down at the time. (-:)
Mark

Re: Just beginning problem

mark.carr...@aetion.com (Mark T. B. Carroll) — Sun, 18 Жов 2009 19:50:15 UT

Quite, if you're making a good effort to try, we'll still be able to
tell even if the questions are dumb. And for what it's worth, I've asked
my fair share of dumb questions too. (-:
Mark

Re: Just beginning problem

e...@mountaincable.net (Chris Saunders) — Sun, 18 Жов 2009 19:37:46 UT

Thanks for the tip. Perhaps the information on MSDN is not a brain damaged
as you think. What you spoke about is described and spoken about in the
lecture series I was watching. I was just trying to enter some of the
example code shown into GHCi. I am reading the manual for GHCi but have not

Re: Just beginning problem

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Sun, 18 Жов 2009 19:26:42 UT

Don't be ashamed, just ask. There are no dumb questions, just dumb answers.
I'm not using Windows, but AFAIK, "mirc" is a popular client for Windows.
- Dirk

Re: Just beginning problem

e...@mountaincable.net (Chris Saunders) — Sun, 18 Жов 2009 19:13:03 UT

I rather like this suggestion. I have never used IRC. Could you suggest a
program to use on Windows. Right now I am having a few difficulties that
I'm almost ashamed to ask about.
Regards
Chris Saunders

Re: Just beginning problem

e...@ertes.de (Ertugrul Söylemez) — Sun, 18 Жов 2009 05:04:06 UT

Your original question has been answered. I just like to add something
very important.
Simply put, this is not the way you would define a 'myAdd' function in
Haskell. Your function doesn't take two arguments, but only one
argument, a tuple of two numbers, notated by (x, y). Here is how to do
it properly:

Re: Just beginning problem

mark.carr...@aetion.com (Mark T. B. Carroll) — Sun, 18 Жов 2009 02:15:44 UT

Oh, an online Microsoft community thing, thank you! And I had been
wondering if it was some local public access station. (Ours happens to
be on channel 9 on cable.)
Mark

Re: Just beginning problem

(Paul Rubin) — Sat, 17 Жов 2009 23:32:34 UT

[link]

Re: Just beginning problem

mark.carr...@aetion.com (Mark T. B. Carroll) — Sat, 17 Жов 2009 23:23:44 UT

No problem, dumb questions are at least quickly answered. (-:
So what is this Channel 9 that teaches Haskell? Sounds intriguing.
Mark

Re: Just beginning problem

(Paul Rubin) — Sat, 17 Жов 2009 23:05:20 UT

IRC might be a better place than Usenet to seek this kind of help. If
you have an IRC client, hang out on #haskell. It is a friendly place
and you'll learn a lot.

Re: Just beginning problem

e...@mountaincable.net (Chris Saunders) — Sat, 17 Жов 2009 22:42:55 UT

I very much appreciate your help. I'm afraid I may be full of dumb
questions for awhile. For a little while, I don't think I'll be trying to
create any source files but I'll try to remember the tip.
Regards
Chris Saunders

Re: Just beginning problem

mark.carr...@aetion.com (Mark T. B. Carroll) — Sat, 17 Жов 2009 22:14:47 UT

When typing functions into GHCi, add a `let' in front:
Prelude> let myadd (x,y) = x + y
Prelude> :info myadd
myadd :: (Num t) => (t, t) -> t -- Defined at <interactive>:1:4-8
Prelude>
If you put it in a file instead and use :load to load it (or :reload to
reload it), you don't put the `let' in the definition in the file.

Just beginning problem

e...@mountaincable.net (Chris Saunders) — Sat, 17 Жов 2009 21:52:52 UT

I am just beginning to learn Haskell. Just for starters I'm watching a
video lecture from Channel 9. The lecturer defines a function like this
"myadd (x,y) = x + y". When I enter this into GHCi I get the error message
":1:12: parse error on input `='". Could I get a simple explanation of
this?

Re: Double -> Rational conversion?

haberg_20080...@math.su.se (Hans Aberg) — Fri, 09 Жов 2009 08:45:19 UT

If one wants to have a series of approximants, one can use continued
fraction convergents. There is a fast algorithm on the Wikipedia page.
I have found it useful in music. For example, in my program:
> crat(cf (logBase 2 (3/2)) 8)
[0 % 1,1 % 1,1 % 2,3 % 5,7 % 12,24 % 41,31 % 53,179 % 306]
Here, "cf x n" computes n continued fractions of the Double x, and

Re: Rational -> Double conversion?

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Thu, 08 Жов 2009 21:45:00 UT

The library code uses fromRat for fromRational in the instance for
Double, so in terms of efficiency, they should be the same.
BTW, one can also convert a Double to a fraction:
Prelude> toRational pi
884279719003555%28147497671065 6
- Dirk

Re: Rational -> Double conversion?

fu...@hawaii.edu (Ryo) — Fri, 09 Жов 2009 03:20:58 UT

On Oct 8, 3:07 am, use...@mkarcher.dialup.fu-berl in.de
Thank you for your response! I'll use Hoogle next time. Without
knowing fromRat[ional], I was using such a tedious function as
rat_to_frac r =
(fromIntegral (numerator r))
/ (fromIntegral (denominator r))

Re: whither operational semantics?

rao...@gmail.com (raould) — Fri, 09 Жов 2009 00:44:43 UT

as an aside: reading the Clojure list, i often see people tripped up
by laziness there, even w/out the added problem of ambiguous
evaluation order iiuc. i think laziness needs to be really
stupendously explicit in the ascii sources.
heap on top of that the issue of changing reduction order and oy veh.

Re: Rational -> Double conversion?

use...@mkarcher.dialup.fu-berlin.de (Michael Karcher) — Thu, 08 Жов 2009 13:07:33 UT

Just as an Hint how to find that: Use Hoogle.
[link]
Enter the type of the function you look for (Rational->Double).
First two hits are fromRat and fromRational. It might be that
fromRat is more efficient then fromRational, as fromRat requires
(RealFrac a) instead of just (Fractional a).

Re: Rational -> Double conversion?

use...@mkarcher.dialup.fu-berlin.de (Michael Karcher) — Thu, 08 Жов 2009 10:02:43 UT

It's
fromRational :: (Fractional a) => Rational -> a
Regards,
Michael Karcher

Rational -> Double conversion?

fu...@hawaii.edu (Ryo) — Thu, 08 Жов 2009 09:57:43 UT

Hello Haskellers,
I'm a novice Haskell user. I'm wondering how to get an approximate
value in Double of a Rational. I'm doing a little numerical
calculation using Rational to avoid truncation error, but want the
final results printed as Doubles that approximate original Rationals.
(I need this to read the results in Fortran.)

Re: Logger monad

mark.carr...@aetion.com (Mark T. B. Carroll) — Wed, 07 Жов 2009 02:24:26 UT

(snip)
Sounds good.
You can get partway there with some without too much wiggling. For
instance, in Modula-3, in an interface you can declare multiple "partial
revelations" and indeed a full revelation of objects inside the module;
you could reveal the same ones to different extents.
Mark

Re: Logger monad

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Tue, 06 Жов 2009 14:24:55 UT

If he has the sources in the first place. And sometimes it's still
impractical to change the source, for example if the library is already
installed in compiled form on the end-user's machines.
No, because there's no need to treat users of your code like they are
stupid people. Or if you do, they'll hate you :-)

Re: Logger monad

rose.howard-5o6lt...@yopmail.com (Rose Howard) — Tue, 06 Жов 2009 13:50:43 UT

But if the client want to bypass the public interface (it knows what it
does) it could change the interface of the library by modifying the
sources ? usually I hide everything, and if one want to use internal
state he looks at the code and changes what he wants. Isn't it better to
force the user to really know what he is doing ?

Re: Logger monad

mark.carr...@aetion.com (Mark T. B. Carroll) — Sat, 03 Жов 2009 21:56:43 UT

Huh, thank you, yes - I hadn't known about that. When I notice something
would be worth writing, often someone has more than adequately beaten me
to it!
Mark

Re: Logger monad

(Paul Rubin) — Sat, 03 Жов 2009 21:02:00 UT

Yeah, I think this is what Iteratee aims to do in a more general way.
I haven't been able to understand it well enough to use it, so far.
[link]

Re: Logger monad

f...@deneb.enyo.de (Florian Weimer) — Sat, 03 Жов 2009 16:38:32 UT

* Mark T. B. Carroll:
Exactly.
It still potentially performs imperative reads on pattern matches. It
deals with two practical problems of lazy I/O: closing the input
stream to free resources at the right time, and improved error
handling. It does not deal with the fundamental safety issue.
If it's safe, you can't use pattern matching on lists as a replacement

Re: Logger monad

mark.carr...@aetion.com (Mark T. B. Carroll) — Sat, 03 Жов 2009 15:44:05 UT

hGetContents is certainly a horror, especially as it's not clear from
the signature that there be dragons. At least unsafePerformIO has a hint
in its name. I recently found myself writing a readFile' that seq's the
length of the contents before returning them.
I noticed a "safe lazy IO" thing in Hackage but I haven't yet got around

Re: Logger monad

(Paul Rubin) — Sat, 03 Жов 2009 11:31:38 UT

Do you mean because of lazy i/o? That really seems like a wart in the
language.

Re: Logger monad

f...@deneb.enyo.de (Florian Weimer) — Sat, 03 Жов 2009 11:09:36 UT

* Mark T. B. Carroll:
But this is not true. Any pattern match can cause IO (well, "I") in
Haskell.

Re: Logger monad

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Sat, 03 Жов 2009 07:24:18 UT

Exactly. So what I'm complaining about is library developers who don't
can imagine that a route-around is desired (to extend the functionality),
and hence don't include it in the interface. Which is quite excuseable,
of course one cannot imagine all the ways this code could possibly be
used in the future. And that's the reason why it's a bad idea to

Re: Logger monad

dthierb...@usenet.arcornews.de (Dirk Thierbach) — Sat, 03 Жов 2009 07:33:49 UT

Yes, exactly. My idea of implementing this would be some kind of "module
views": Each module can provide a number of different "export lists".
For sake of an example, say the module M has three export lists called
"public", "protected", and "private", then one could do something like
import M#public

Re: Logger monad

mark.carr...@aetion.com (Mark T. B. Carroll) — Sat, 03 Жов 2009 04:31:04 UT

I thus audaciously put thoughts into Dirk's head: Paradoxically, perhaps
what is wanted is lack of straitjacket _and_ lack of restriction. That
is, let the user of the module/object/whatever grobble in its internals
as much as they like, but only insofar as they somehow reflect that
particular taint in the types of their functions that do so. I don't

* FLOPS 2010: Last Call for Papers *

matthias.bl...@gmail.com (Matthias) — Sat, 03 Жов 2009 02:42:10 UT

Re: Logger monad

mark.carr...@aetion.com (Mark T. B. Carroll) — Fri, 02 Жов 2009 21:06:01 UT

Ah, yes. I guess here we have a question of discouraging versus being
sure they don't; on this occasion, I needed much assurance, enough that
I didn't trust myself, but that's admittedly not the usual situation.
(snip)
Certainly there are times when the obvious generalization to me is not
the obvious one to someone else. This especially happens when I thread

Re: Logger monad

(Paul Rubin) — Fri, 02 Жов 2009 20:54:29 UT

Isn't that enforcement the precise point of a type system? "A
tractable syntactic method for proving the absence of certain program
behaviors by classifying phrases according to the kinds of values they
compute" (Pierce, TaPL). If some type of route-around is desired
then it should be included in the interface.

comp.lang.haskell Google Group

Re: Transparent results cache

Re: Transparent results cache

Re: Transparent results cache

Transparent results cache

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Re: happs coming alone?

Re: happs coming alone?

happs coming alone?

Re: monads for lambda calculus

Re: monads for lambda calculus

Re: monads for lambda calculus

monads for lambda calculus

*** extended deadline: FLOPS 2010: Last Call for Papers ***

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Re: Just beginning problem

Just beginning problem

Re: Double -> Rational conversion?

Re: Rational -> Double conversion?

Re: Rational -> Double conversion?

Re: whither operational semantics?

Re: Rational -> Double conversion?

Re: Rational -> Double conversion?

Rational -> Double conversion?

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

Re: Logger monad

*** FLOPS 2010: Last Call for Papers ***

Re: Logger monad

Re: Logger monad

* extended deadline: FLOPS 2010: Last Call for Papers *

* FLOPS 2010: Last Call for Papers *