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Today's Topics:

   1.   How to fold a map (Tim Baumgartner)
   2.  question about comprehension or array creation (cchang)
   3. Re:  How to fold a map (Lyndon Maydwell)
   4. Re:  question about comprehension or array        creation
      (Daniel Fischer)
   5.  Cleaning up after the Close button is pressed (Colin Hume)
   6. Re:  question about comprehension or array        creation (Tim Perry)
   7.  haskell for FPGAS (David Blubaugh)
   8. Re:  Cleaning up after the Close button is        pressed
      (Stephen Tetley)


----------------------------------------------------------------------

Message: 1
Date: Sat, 15 Jan 2011 13:57:16 +0100
From: Tim Baumgartner <baumgartner....@googlemail.com>
Subject: [Haskell-beginners]  How to fold a map
To: beginners@haskell.org
Message-ID:
        <aanlktiky4ohowvhrtrok4ffrcyg_kcen6ocrurpll...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

For all those still having problems with their folds (like myself), the
following might be enlightning:
http://www.youtube.com/watch?v=3063VGrrAdg

Tim
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Message: 2
Date: Sat, 15 Jan 2011 14:19:05 +0000 (UTC)
From: cchang <djvsr...@gmail.com>
Subject: [Haskell-beginners] question about comprehension or array
        creation
To: beginners@haskell.org
Message-ID: <loom.20110115t145734-...@post.gmane.org>
Content-Type: text/plain; charset=us-ascii

Hi,

I tried to create an array like the following.

"array (1,3) [(1,1), (2,2), (3,3)]"

through code in .hs
e = [1,2,3]
array (1,3) [(i,v) | i<-[1..3], v<-e]

but I got
"array (1,3) [(1,3), (2,3), (3,3)]"

why v is always 3 in this case? Can anyone shed some light on this?

Thanks,





------------------------------

Message: 3
Date: Sat, 15 Jan 2011 22:37:44 +0800
From: Lyndon Maydwell <maydw...@gmail.com>
Subject: Re: [Haskell-beginners] How to fold a map
To: Tim Baumgartner <baumgartner....@googlemail.com>
Cc: beginners@haskell.org
Message-ID:
        <AANLkTi=ogzbcz6qa-ee3huw3rghzrbzsvcenhsxqx...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8

Oh you~

On Sat, Jan 15, 2011 at 8:57 PM, Tim Baumgartner
<baumgartner....@googlemail.com> wrote:
> For all those still having problems with their folds (like myself), the
> following might be enlightning:
> http://www.youtube.com/watch?v=3063VGrrAdg
>
> Tim
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>



------------------------------

Message: 4
Date: Sat, 15 Jan 2011 15:45:16 +0100
From: Daniel Fischer <daniel.is.fisc...@googlemail.com>
Subject: Re: [Haskell-beginners] question about comprehension or array
        creation
To: beginners@haskell.org
Cc: cchang <djvsr...@gmail.com>
Message-ID: <201101151545.17159.daniel.is.fisc...@googlemail.com>
Content-Type: text/plain;  charset="iso-8859-1"

On Saturday 15 January 2011 15:19:05, cchang wrote:
> Hi,
>
> I tried to create an array like the following.
>
> "array (1,3) [(1,1), (2,2), (3,3)]"
>
> through code in .hs
> e = [1,2,3]
> array (1,3) [(i,v) | i<-[1..3], v<-e]
>
> but I got
> "array (1,3) [(1,3), (2,3), (3,3)]"
>
> why v is always 3 in this case? Can anyone shed some light on this?
>

Because [(x,y) | x <- list1, y <- list2] gives you the cartesian product of 
the two lists [each element of the first paired with each of the second], 
thus

[(i,v) | i <- [1 .. 3], v <- e]
  = [(1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)]

and (as a known deviation from the Haskell Report), GHC overwrites array 
elements with multiple definitions on creation (according to the report, it 
should throw an error, but checking for duplicates would be too 
inefficient). Thus, with the list above, in each slot the three values 1, 2 
and 3 are written (in that order), the last is the one you see afterwards.

What you want is one of

array (1,3) $ zip [1 .. 3] e

{-# LANGUAGE ParallelListComp #-}
-- Note the two `|'
array (1,3) [(i,v) | i <- [1 .. 3] | v <- e]

or equivalent.



------------------------------

Message: 5
Date: Sat, 15 Jan 2011 11:16:11 -0800
From: Colin Hume <lightwin...@hotmail.com>
Subject: [Haskell-beginners] Cleaning up after the Close button is
        pressed
To: <beginners@haskell.org>
Message-ID: <snt140-w5693c7a0d077d05aea3efea2...@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"


Hi everyone,

I have to perform cleanup when my application terminates. GHC.ConsoleHandler 
handles cleanup from Ctrl-C and Ctrl-Break very nicely under Windows. 
Unfortunately, the RTS does not support delivery of the Close button event. The 
reason given in rts/win32/ConsoleHandler.c is that an improperly-written 
Haskell handler will prevent the user from being able to kill the application.

I have a few questions about this.

1) Is there a different way of cleaning up on Windows after the Close button is 
pressed?

2) It seems strange that GHC intentionally prevents the application from
 cleaning up in order to guarantee that it will terminate as the user 
expects. Why is it not the application developer's responsibility to 
ensure that it can be killed?


Thanks,
Colin
                                          
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Message: 6
Date: Sat, 15 Jan 2011 21:52:04 -0800 (PST)
From: Tim Perry <perry2...@yahoo.com>
Subject: Re: [Haskell-beginners] question about comprehension or array
        creation
To: cchang <djvsr...@gmail.com>, beginners@haskell.org
Message-ID: <50058.51238...@web161407.mail.bf1.yahoo.com>
Content-Type: text/plain; charset=us-ascii

The docs say:

 [(i, e)] a list of associations of the form (index, value). Typically, this 
list will be expressed as a comprehension. An association '(i, x)' defines the 
value of the array at index i to be x. 


I think the important part is that the array is used as a lookup for the values 
to associate with the array. The lookup returns a ?random? one of the three 
values in the list of tuples that have 1 as the first index. In this case it 
happens to be 3. And so on.

This may help:
  Prelude Array> let e = [1,2,3]
Prelude Array> array (1,3) [(i,v) | i<-[1..3], v<-e]
array (1,3) [(1,3),(2,3),(3,3)]
Prelude Array> array (1,9) [(i,v) | i<-[1..3], v<-e]
array (1,9) [(1,3),(2,3),(3,3),(4,*** Exception: (Array.!): undefined array 
element
Prelude Array> 

It couldn't look up a value for 4 so it failed...

Does that help?

--Tim



----- Original Message ----
From: cchang <djvsr...@gmail.com>
To: beginners@haskell.org
Sent: Sat, January 15, 2011 6:19:05 AM
Subject: [Haskell-beginners] question about comprehension or array creation

Hi,

I tried to create an array like the following.

"array (1,3) [(1,1), (2,2), (3,3)]"

through code in .hs
e = [1,2,3]
array (1,3) [(i,v) | i<-[1..3], v<-e]

but I got
"array (1,3) [(1,3), (2,3), (3,3)]"

why v is always 3 in this case? Can anyone shed some light on this?

Thanks,



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Beginners mailing list
Beginners@haskell.org
http://www.haskell.org/mailman/listinfo/beginners




------------------------------

Message: 7
Date: Sat, 15 Jan 2011 22:44:22 -0800 (PST)
From: David Blubaugh <davidblubaugh2...@yahoo.com>
Subject: [Haskell-beginners] haskell for FPGAS
To: beginners@haskell.org
Message-ID: <73108.58798...@web113308.mail.gq1.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"

To All,
?
?
Has anyone developed HASKELL FOR FPGA development ??
?
Thank You,
?
Daid Blubaugh
?
?


      
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Message: 8
Date: Sun, 16 Jan 2011 08:10:38 +0000
From: Stephen Tetley <stephen.tet...@gmail.com>
Subject: Re: [Haskell-beginners] Cleaning up after the Close button is
        pressed
To: Colin Hume <lightwin...@hotmail.com>
Cc: beginners@haskell.org
Message-ID:
        <aanlktiklrv4p7wmqk3saunwibramd961bhemokp2g...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Hi Colin

If no-one has answered your query off-list you might want to punt it
to the GHC users list or Haskell-cafe.

Questions about a specific technology generally seem to get answered
quicker on Haskell-cafe than Beginners, if they are specifically about
GHC they seem to get the best answers on the GHC list.

The Beginners list seems the best place for "general" elementary
Haskell questions (answers are usually more explanatory than they
would be on Haskell-cafe), but not questions about specific libraries
or GHC specifics as such questions can be missed by people with the
specific knowledge.

Best wishes

Stephen



------------------------------

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