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Today's Topics:
1. Re: state monad (Brandon Allbery)
2. Re: Fwd: Implementing a spellchecker - problem with
Data.HashTable performance (Rados?aw Szymczyszyn)
3. Cyclic structures (David Tchepak)
4. Re: Cyclic structures (Adrien Haxaire)
5. Re: Fwd: Implementing a spellchecker - problem with
Data.HashTable performance (Osager Prairie)
----------------------------------------------------------------------
Message: 1
Date: Sun, 22 Apr 2012 06:43:21 -0400
From: Brandon Allbery <allber...@gmail.com>
Subject: Re: [Haskell-beginners] state monad
To: Paul Higham <polyg...@mac.com>
Cc: Beginners@haskell.org
Message-ID:
<cakfcl4xwfchq0bhxq2uup-hwk5sx12q5ax1xpuek3tprmtp...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Sun, Apr 22, 2012 at 04:40, Paul Higham <polyg...@mac.com> wrote:
> stackPlay.hs:6:7: Not in scope: data constructor `State'
>
> Please excuse the cognitive deficit, but I cannot figure out why this
> should not work as advertised.
>
Not your fault; things were rearranged in the library, and `State` is no
longer a distinct type (it's `StateT Identity` now). `state` (lowercase)
is the replacement for the old `State` constructor.
--
brandon s allbery allber...@gmail.com
wandering unix systems administrator (available) (412) 475-9364 vm/sms
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Message: 2
Date: Sun, 22 Apr 2012 16:58:52 +0200
From: Rados?aw Szymczyszyn <lav...@gmail.com>
Subject: Re: [Haskell-beginners] Fwd: Implementing a spellchecker -
problem with Data.HashTable performance
Cc: beginners@haskell.org
Message-ID:
<CAG=dco3c6ujnx-qubyjwl05jpzow+bhn8q_egn-uad0zy4p...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Thank you all for thoughts and suggestions. I've been tracking them as
they appeared, but being busy with university assignments, couldn't
try them out yet.
In the meantime, however, Karol Samborski investigated the issue
further and found the cause of poor performance -- somehow using
HashTable.newHint doesn't play well with HashTable.update. Simply
changing newHint to hint gives me execution time of about 12s (on my
rather slowish AMD Fusion 1.6GHz laptop) with a dataset of ~1.35mln
words.
It's evidently a bug, as newHint would hardly be expected to slow
things down. I'm yet to discover how to properly report it.
Thanks again to all who responded and especially to Karol for solving
the problem.
Best regards,
Radek Szymczyszyn
------------------------------
Message: 3
Date: Mon, 23 Apr 2012 16:00:09 +1000
From: David Tchepak <tche...@gmail.com>
Subject: [Haskell-beginners] Cyclic structures
To: beginners@haskell.org
Message-ID:
<CAOeLS_8WCrDz_QVecbJ=bhfj66k22586y9x3+ceufd+ufre...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
I'm currently reading the first edition of "Introduction to Functional
Programming" by Richard Bird and Philip Wadler. Section 7.6 is on cyclic
structures, and has the following example:
ones = forever 1
forever x = x : forever x
Which, after 5 evaluations, produces a graph like:
1 : 1 : 1 : 1 : 1 : forever 1
The book then has a re-written version of `forever` that looks like this:
forever x = zs
where zs = x : zs
Which instead produces a cyclic structure:
* 1 :
^-----|
So it takes up a fixed amount of space, despite being an infinite list.
I was hoping someone could explain the difference between the first and
second `forever`s for me. Does the second version become a cyclic graph
because the `zs` intermediate expression has no additional arguments so
doesn't need to be reduced further? Or do both end up being optimised the
same by GHC? (my newbie attempts to profile show the second takes up a bit
less space, but I'm not sure if I'm measuring it right).
Appreciate any help.
Regards,
David
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Message: 4
Date: Mon, 23 Apr 2012 09:45:53 +0200
From: Adrien Haxaire <adr...@haxaire.org>
Subject: Re: [Haskell-beginners] Cyclic structures
To: <beginners@haskell.org>
Message-ID: <04475597a810a1dd7cf901692c6b2...@haxaire.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Hi,
I do not have the answer to your question, but you might be interested
in the video about streams by Graham Hutton:
http://channel9.msdn.com/Shows/Going+Deep/C9-Lectures-Graham-Hutton-How-To-Be-More-Productive
Adrien
On Mon, 23 Apr 2012 16:00:09 +1000, David Tchepak wrote:
> Im currently reading the first edition of "Introduction to Functional
> Programming" by Richard Bird and Philip Wadler. Section 7.6 is on
> cyclic structures, and has the following example:
>
> ? ones = forever 1
> ? forever x = x : forever x
>
> Which, after 5 evaluations, produces a graph like:
>
> ? 1 : 1 : 1 : 1 : 1 : forever 1
>
> The book then has a re-written version of `forever` that looks like
> this:
>
> ? forever x = zs
> ? ? where zs = x : zs
>
> Which instead produces a cyclic structure:
>
> ? * 1 :?
> ? ^-----|
>
> So it takes up a fixed amount of space, despite being an infinite
> list.
>
> I was hoping someone could explain the difference between the first
> and second `forever`s for me. Does the second version become a cyclic
> graph because the `zs` intermediate expression has no additional
> arguments so doesnt need to be reduced further? Or do both end up
> being optimised the same by GHC? (my newbie attempts to profile show
> the second takes up a bit less space, but Im not sure if Im measuring
> it right).
>
> Appreciate any help.
> Regards,
> David
--
Adrien Haxaire
www.adrienhaxaire.org | @adrienhaxaire
------------------------------
Message: 5
Date: Mon, 23 Apr 2012 11:01:00 +0200
From: Osager Prairie <osagerprai...@gmail.com>
Subject: Re: [Haskell-beginners] Fwd: Implementing a spellchecker -
problem with Data.HashTable performance
To: Rados?aw Szymczyszyn <lav...@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<ca+q7gyaehncsmfqwm73rxequen5kqd2ca9pesmn9tjg-ney...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi:
Your post is very interesting.
I'm also a beginner so can not offer you much suggestions.
Only that I saw this book the other day and think it might be helpful for
you.
Computational Semantics with Functional
Programming<http://www.amazon.com/Computational-Semantics-Functional-Programming-Eijck/dp/0521760305>
This book use haskell as the programming language
Best regards
On Sun, Apr 22, 2012 at 4:58 PM, Rados?aw Szymczyszyn <lav...@gmail.com>wrote:
> Thank you all for thoughts and suggestions. I've been tracking them as
> they appeared, but being busy with university assignments, couldn't
> try them out yet.
>
> In the meantime, however, Karol Samborski investigated the issue
> further and found the cause of poor performance -- somehow using
> HashTable.newHint doesn't play well with HashTable.update. Simply
> changing newHint to hint gives me execution time of about 12s (on my
> rather slowish AMD Fusion 1.6GHz laptop) with a dataset of ~1.35mln
> words.
>
> It's evidently a bug, as newHint would hardly be expected to slow
> things down. I'm yet to discover how to properly report it.
>
> Thanks again to all who responded and especially to Karol for solving
> the problem.
>
> Best regards,
> Radek Szymczyszyn
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
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