YANETUT.

Definition of bind operator for State monad?

noreply@blogger.com (kazuya) — Sat, 20 Sep 2008 02:54:00 +0000

instance Monad (State s) where 
    return a        = State $ \s -> (a,s)
    (State x) >>= f = State $ \s -> let (v,s') = x s in runState (f v) s'

From Control.Monad.State.Lazy:


instance Monad (State s) where
    return a = State $ \s -> (a, s)
    m >>= k  = State $ \s -> let
        (a, s') = runState m s
        in runState (k a) s

Hmm, how and why are they different? The latter one makes sense to me, but I cannot get the part to apply x to s in the former one.

Update:

I got it. I just did not notice that the former used pattern matching against to deconstruct the first argument (State x), where as the latter used field selector (runState). Note that the State monad is declared as follows:

newtype State s a = State { runState :: s -> (a, s) }

test from n810

noreply@blogger.com (kazuya) — Mon, 11 Feb 2008 18:36:00 +0000

here here

Book Cataloging

noreply@blogger.com (kazuya) — Sun, 06 Jan 2008 04:40:00 +0000

It's been a while since my last post... actually I started writing this article one month ago and still I am writing this. In fact I sometimes make a reply for an email almost one year after receiving it. That was how we did in pen and paper era.

Technologies have made it easier to retrieve information, but have not much helped creating or generating something really new.

Now, I am talking about book cataloging, inspired by a Slashdot article: Slashdot | The Home Library Problem Solved. Although I do not have much interest in physical home libraries (it is not practical to build a decent home library in this small condo, after all), cataloging books has been one of my sources of headache.

My requirements are not ambitious:

Accessible through Web
Can handle multilingual titles
Easy entry

The first requirement is crucial and stand-alone applications such as Delicious Library and Booxter are excluded, though they are cool and comfortable to use. You can find information on open source cataloging software such as tellico here.

As the little widget in the sidebar of this blog shows, I have used LibraryThing for some time, but it has several problems including this. Actually I have tried Hondana.org, which is targeted at Japanese readers, but it is not about cataloging. Hondana.org focuses on social networking through books, and features not relevant to such a goal are not great.

From the Slashdot article I found goodreads, yet another LibraryThing. But it does not have collision issue like LT and seems to work flawlessly for now. Worth a try.

Just an additional requirement is lending management, and all of above have little support or nothing for that. There are such systems as Webrary and Koha, but they are both overkill for me.

And just for your information, you can find a detailed list of cataloging software here.

Using CueCat USB barcode reader with Mac OS X

noreply@blogger.com (kazuya) — Sat, 15 Dec 2007 03:19:00 +0000

I got it from LibraryThing (also available from Amazon), to ease the task of entering books from my library into the database (presumably LT, but will consider using Delicious Library when it's 2.0 is available).

Unfortunately CueCat spits out encrypted data and needs a simple modification before it sends out any meaningful digits. I followed instruction at this site and it worked fine.

Note that you do not need this modification if you use it only on LibraryThing... it automatically decrypts the code for you.

Web Hosting

noreply@blogger.com (kazuya) — Sat, 08 Dec 2007 12:45:00 +0000

I have been planning to migrate this site to a virtual private server (FYI it's now hosted at swishmail.com). Swishmail is not the greatest web hosting service, and I do need full control of my server in order to do some experiments.

Googling around with search phrase like "darcs hosting dreamhost", because I want to use darcs, and someone recommended dreamhost for its price, gave me a link to a blog article. I have no idea whether his case really stands, but anyhow it led me to several VPS services, like unixshell, VPSlink, MEMSET, JohnCompany.

Among them unixshell seems to be good, but as unixshell currently offers no new account, I would take their alternative, TekTonic. One of the features I like about it is their unmetered plan, which does not limit monthly transfer amount, but just limits the bandwidth per second, for example 1 Mbps.

Book collision on LibraryThing

noreply@blogger.com (kazuya) — Fri, 07 Dec 2007 16:28:00 +0000

I resumed using LibraryThing recently and added several books more (you might notice books selected from my online library in the sidebar). Among them, the entry for Iwanami Mathematics Dictionary (yes, it's in Japanese) on LT got weird.

The entry got mixed (or combined, as a post in LT group forum told) with some strange manga book which I am never aware of. The post said it was caused by hash collision... what a poor implementation!

Joe Armstrong's Erlang Book

noreply@blogger.com (kazuya) — Fri, 07 Dec 2007 16:07:00 +0000

As some of you may know, I am responsible for translating Joe Armstrong's new book about Erlang into Japanese.

Translation is close to finish now, though still I have to do with inputs from reviewers and catch up to the latest version of the original English version. And it's nice if I can include updates from R12B-0 release if any, but that release seems not stable now.

So I am supposed not to make a fuss with Haskell. I know.

Installing GHC 6.8.1 on Mac OS X Leopard (x86)

noreply@blogger.com (kazuya) — Fri, 07 Dec 2007 15:06:00 +0000

As reported in glasgow-haskell-users, you need to be a bit careful to use this configuration.

Although I took care of those libgmp and readline dependency thingies, following error was persistent when I tried to build it:

... snipped
installPackage: Multiple files with extension buildinfo
make[1]: *** [install.library.Cabal] Error 1
make: *** [install] Error 2

Under libraries/Cabal directory there was a file named buildinfo2.buildinfo, but no other file with .buildinfo extension... yes, actually there was, it was ._buildinfo2.buildinfo. After removing this file the build was successful.

It was likely that this offensive file snuck into there during preparing the archive. I expanded the archive using tar command on the command line, but I should have used the Archive Utility, which handles those dot-files correctly.

Anyhow, that's how I wasted my precious four nights :-(

The Mysterious ⊥

noreply@blogger.com (kazuya) — Mon, 03 Dec 2007 14:07:00 +0000

Searching the symbol ⊥, which is used to represent 'bottom' in Haskell, with Google gave me no answer. I mean, no alternative suggestions, nothing.

Weird.

Problems with Skyeye the ARM simulator on Mac OS X

noreply@blogger.com (kazuya) — Mon, 26 Nov 2007 16:52:00 +0000

These days I have tried to make skyeye ARM simulator work on Mac OS X with full options enabled, but still to no avail.

I know it should work without DBCT (direct byte code translation) and BFD as README says, but DBCT is beneficial for my intended workloads.

As of 1.2.4, it does not pass even the configuration check if you enable DBCT and BFD. Though a little hack in the check script for DBCT made it go through the check (with BFD disabled), build fails with:

ld: in binary/libarm.a(arm2x86.o), in section __TEXT,__text reloc 40: R_ABS reloc but no absolute symbol at target address

collect2: ld returned 1 exit status

Probably I need to use gnu ld instead.

Parser in Haskell

noreply@blogger.com (kazuya) — Fri, 23 Nov 2007 07:24:00 +0000

The first chapter of the book is mostly about writing a parser in Miranda (the code is in Haskell, though).

It does not use monads. You can see how the implementation can be refined with monads if you compare it with a monadic parser of today.

Carbon Emacs

noreply@blogger.com (kazuya) — Tue, 20 Nov 2007 14:52:00 +0000

So I abandoned Aqua Emacs and am now using Carbon Emacs. Emacs variants such as XEmacs, Meadow, Aqua Emacs all failed with me... I just didn't feel like Emacs. GNU Emacs, I mean.

A little Haskeller

noreply@blogger.com (kazuya) — Tue, 20 Nov 2007 14:37:00 +0000

Started reading Implementing functional languages: a tutorial.

I'm not much interested in writing a compiler (I wish I could, though), but this tutorial is useful for me. After all, a compiler implementation needs almost every kind of topics. And Simon Peyton Jones is a great author - you can see that from his other papers.

This book was written for Miranda, an ancestor of Haskell. That's okay, but the code in text is in Miranda while sample code seems to be in Haskell. They have many in common and I can easily guess how the description in text part should be fixed, still it's annoying.

I read this book (the dead tree version available from CafePress) while commuting on the train and unable to do exercises. Good excuse to get Nokia N810 or iRex iLiad?

Does it burn up to Fahrenheit 451?

noreply@blogger.com (kazuya) — Tue, 20 Nov 2007 13:28:00 +0000

As an Amazon-dependent bookworm, I have to throw some words about Amazon Kindle, though I cannot get a touch on it here in Tokyo.

I had used 1st generation Sony Reader for a month or so before, and from that experience, I find several points remarkable:

Distibution model - Distribution is done through EVDO wireless network without no 'visible' fee. Of course the cost is included in the price - you can think of it as 'printing' through wireless network to the Kindle device instead of printing on paper. You don't pay for paper and ink, but pay for network.
User interface - The vertical LCD in the right and the scroll wheel seems to work as a workaround to the slow redraw problem of E-ink. It is a huge improvement from existing E-ink based devices. UI of Sony Reader was, well, just not adequate. It presented all visual feedbacks on sluggish E-ink display, which made the user interface uncomfortable.
Faster screen redraw - From the video on the product page, you can see the screen is redrawn in a flash, as the one of latest Sony Reader 505 is heralded. I don't think former generation is not usable at all, but the faster the better.
Annotations - You can add annotations using the keyboard. That's another advantage over Sony Reader.

One of the problems for me is, as others pointed out, it does not support PDF natively. Amazon says it can convert user made PDFs to Kindle format, but from bitter experience of PDF on Sony Reader, I don't expect much. Probably I opt for iRex iLiad just for that.

As for its 'bookness' (Jeff Bezos touted it has all features that dead tree books have), it achieved quite well. Though some complain just because it is not made of paper and ink ("It does not smell ink!"), I have no attachment to dead tree books. Of course it cannot be used without electricity, but dead tree books have their own weakness.

Anyway I will wait and see how it goes, until it is available in Japan.

入力ミス

noreply@blogger.com (kazuya) — Fri, 22 Jun 2007 14:58:00 +0000

「コマンド」と入力しようとして何度も「コメント」と入力してしまう。
それにしてもMacBookのキーボードはよくない。ずっとThinkPad T21を使っていたのでなおさらそう思う。せめてMacBook Proにしておけばまだましだったかも。ThinkPadでMac OS Xが動けば最高なんだが。

Aquamacs

noreply@blogger.com (kazuya) — Wed, 20 Jun 2007 22:00:00 +0000

LC_ALLをja_JP以外にしないとsite-start.el (から呼び出されてるどこか)でエラーになる。多分文字コード変換関係?

Test

noreply@blogger.com (kazuya) — Tue, 19 Jun 2007 15:44:00 +0000

ちょっとテスト。