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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 <[email protected]>
Subject: [Haskell-beginners] How to fold a map
To: [email protected]
Message-ID:
<[email protected]>
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 <[email protected]>
Subject: [Haskell-beginners] question about comprehension or array
creation
To: [email protected]
Message-ID: <[email protected]>
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 <[email protected]>
Subject: Re: [Haskell-beginners] How to fold a map
To: Tim Baumgartner <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=UTF-8
Oh you~
On Sat, Jan 15, 2011 at 8:57 PM, Tim Baumgartner
<[email protected]> 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
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
------------------------------
Message: 4
Date: Sat, 15 Jan 2011 15:45:16 +0100
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-beginners] question about comprehension or array
creation
To: [email protected]
Cc: cchang <[email protected]>
Message-ID: <[email protected]>
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 <[email protected]>
Subject: [Haskell-beginners] Cleaning up after the Close button is
pressed
To: <[email protected]>
Message-ID: <[email protected]>
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 <[email protected]>
Subject: Re: [Haskell-beginners] question about comprehension or array
creation
To: cchang <[email protected]>, [email protected]
Message-ID: <[email protected]>
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 <[email protected]>
To: [email protected]
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,
_______________________________________________
Beginners mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 7
Date: Sat, 15 Jan 2011 22:44:22 -0800 (PST)
From: David Blubaugh <[email protected]>
Subject: [Haskell-beginners] haskell for FPGAS
To: [email protected]
Message-ID: <[email protected]>
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 <[email protected]>
Subject: Re: [Haskell-beginners] Cleaning up after the Close button is
pressed
To: Colin Hume <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
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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End of Beginners Digest, Vol 31, Issue 15
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