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Today's Topics:
1. Re: Architecture and monads (Amy de Buitl?ir)
2. A newbie question (Mianlai Zhou)
3. Re: A newbie question (Brandon S Allbery KF8NH)
4. Re: A newbie question (Mianlai Zhou)
----------------------------------------------------------------------
Message: 1
Date: Wed, 8 Dec 2010 14:27:05 +0000
From: Amy de Buitl?ir <a...@nualeargais.ie>
Subject: Re: [Haskell-beginners] Architecture and monads
To: Heinrich Apfelmus <apfel...@quantentunnel.de>
Cc: beginners@haskell.org
Message-ID:
<aanlktindonkqy6jjt5nkjz52chvjogtzqxvpr4dnn...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
> My advice is this: instead of using a state monad, use a monad that has
> an independent interpretation. (You may *implement* it in terms of the
> state monad, but you may not *think* of it as a state monad).
Thank you so much. The advice and links you gave me are very helpful.
------------------------------
Message: 2
Date: Thu, 9 Dec 2010 00:18:45 +0800
From: Mianlai Zhou <mian...@gmail.com>
Subject: [Haskell-beginners] A newbie question
To: beginners@haskell.org
Message-ID:
<aanlktinmnf06+dytuof=+vseboh5vbv6rexgvd+mk...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Hello All,
Today I wrote my first Haskell program, which is
module Main
where
f 1 = 1
f n = n*f(n-1)
main = putStrLn (show (f 5))
After compilation, this program runs with no problem and gives 120 (which is
correct).
I have two questions though:
1. What does "where" in line 2 mean? Why I should put it here in this place?
If there is no "where"
here, the program cannot run. But what is the syntactical meaning of
"where"?
2. Why this module can end without an "end" sentence? And what are the blank
lines treated as?
Thank you for your answer, well, in advance. These are newbie questions
indeed.
Best wishes,
Mr. Zhou
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Message: 3
Date: Wed, 08 Dec 2010 11:48:57 -0500
From: Brandon S Allbery KF8NH <allb...@ece.cmu.edu>
Subject: Re: [Haskell-beginners] A newbie question
To: beginners@haskell.org
Message-ID: <4cffb6f9.9090...@ece.cmu.edu>
Content-Type: text/plain; charset=UTF-8
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On 12/8/10 11:18 , Mianlai Zhou wrote:
> 1. What does "where" in line 2 mean? Why I should put it here in this place?
> If there is no "where"
> here, the program cannot run. But what is the syntactical meaning of "where"?
It's just Haskell's syntax convention. Most Haskell declarations have the
format "<whatever> <name> where ..." (module, class, instance; data if GADTs
are enabled; functions also can have "where" clauses introducing local
definitions).
> 2. Why this module can end without an "end" sentence? And what are the blank
> lines treated as?
Haskell doesn't use keywords for delimiters; it mostly uses layout (like
Python but IMO a bit saner) although you can use explicit braces and
semicolons if you really want to. The module declaration is somewhat
special in that you don't have to indent the declarations in its "where"
clause; but the price of this is you can only have one module per file.
(Otherwise you'd have to either use braces or obey the layout rule and
indent everything.)
The blank lines do nothing special.
- --
brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com
system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
electrical and computer engineering, carnegie mellon university KF8NH
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Message: 4
Date: Thu, 9 Dec 2010 01:18:26 +0800
From: Mianlai Zhou <mian...@gmail.com>
Subject: Re: [Haskell-beginners] A newbie question
To: beginners@haskell.org
Message-ID:
<aanlktine5gpn4bcgag4rljofvksr8vxb86dx_zboj...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Brandon,
Thanks a lot for your explanation!
M. Zhou
On Thu, Dec 9, 2010 at 12:48 AM, Brandon S Allbery KF8NH <
allb...@ece.cmu.edu> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 12/8/10 11:18 , Mianlai Zhou wrote:
> > 1. What does "where" in line 2 mean? Why I should put it here in this
> place?
> > If there is no "where"
> > here, the program cannot run. But what is the syntactical meaning of
> "where"?
>
> It's just Haskell's syntax convention. Most Haskell declarations have the
> format "<whatever> <name> where ..." (module, class, instance; data if
> GADTs
> are enabled; functions also can have "where" clauses introducing local
> definitions).
>
> > 2. Why this module can end without an "end" sentence? And what are the
> blank
> > lines treated as?
>
> Haskell doesn't use keywords for delimiters; it mostly uses layout (like
> Python but IMO a bit saner) although you can use explicit braces and
> semicolons if you really want to. The module declaration is somewhat
> special in that you don't have to indent the declarations in its "where"
> clause; but the price of this is you can only have one module per file.
> (Otherwise you'd have to either use braces or obey the layout rule and
> indent everything.)
>
> The blank lines do nothing special.
>
> - --
> brandon s. allbery [linux,solaris,freebsd,perl] allb...@kf8nh.com
> system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu
> electrical and computer engineering, carnegie mellon university KF8NH
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> =ktj3
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>
> _______________________________________________
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