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Today's Topics:
1. Re: A Quantity Type - Integer without the Negative #'s
(aditya siram)
2. Re: A Quantity Type - Integer without the Negative #'s
(Daniel Carrera)
3. Re: SQL Lexer (Keith Sheppard)
4. Re: A Quantity Type - Integer without the Negative #'s
(Magnus Therning)
5. Performance of function defined in a 'where' clause
(Kevin Haines)
6. Re: Performance of function defined in a 'where' clause
(Brent Yorgey)
7. Re: SQL Lexer (Andy Elvey)
8. Re: Performance of function defined in a 'where' clause
(Peter Verswyvelen)
----------------------------------------------------------------------
Message: 1
Date: Sat, 9 May 2009 02:07:10 -0500
From: aditya siram <[email protected]>
Subject: Re: [Haskell-beginners] A Quantity Type - Integer without the
Negative #'s
To: Magnus Therning <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-2022-jp"
Cool, that's really interesting! So is it accurate to say "predicated"
datatypes [1] such as Int and String are provided by Haskell but you cannot
create them or specialize on a subset of them? And there are really only two
types of datatypes, tags [2] and the "predicated" types. Compound datatypes
are just a combination of the two.
-deech
[1] By predicated I mean a datatype that would actually cause a compiler
error ( not a runtime error ) if a method returned an out-of-bounds value.
[2] By tags I mean the data constructors, but I find it easier to think of
them as tags because they can appear alone, eg. data Coins = Penny | Nickel
| Dime | Quarter
where nothing is being constructed.
On Fri, May 8, 2009 at 5:06 PM, Magnus Therning <[email protected]> wrote:
> aditya siram wrote:
>
>> Hi all,
>> Is there a datatype in Haskell that can be used to represent only
>> quantities >= 0? I got bitten by a bug because I forgot to reject an amount
>> that was below zero after applying a decrementing operator. A simple unit
>> test would have caught this, but I was wondering if there was some way of
>> getting the type system to ensure this.
>>
>
> Maybe Word32 (or one of it's siblings) would do? It's basically the same
> as 'unsigned int' in C, so it can under- and over-flow.
>
> /M
>
> --
> Magnus Therning (OpenPGP: 0xAB4DFBA4)
> magnus$B!w(Btherning$B!%(Borg Jabber:
> magnus$B!w(Btherning$B!%(Borg
> http://therning.org/magnus identi.ca|twitter: magthe
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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Message: 2
Date: Sat, 09 May 2009 09:37:53 +0200
From: Daniel Carrera <[email protected]>
Subject: Re: [Haskell-beginners] A Quantity Type - Integer without the
Negative #'s
To: beginners <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
Magnus Therning wrote:
> aditya siram wrote:
>> Hi all,
>> Is there a datatype in Haskell that can be used to represent only
>> quantities >= 0? I got bitten by a bug because I forgot to reject an
>> amount that was below zero after applying a decrementing operator. A
>> simple unit test would have caught this, but I was wondering if there
>> was some way of getting the type system to ensure this.
>
> Maybe Word32 (or one of it's siblings) would do? It's basically the
> same as 'unsigned int' in C, so it can under- and over-flow.
What's under-flow?
------------------------------
Message: 3
Date: Sat, 9 May 2009 08:56:56 -0400
From: Keith Sheppard <[email protected]>
Subject: Re: [Haskell-beginners] SQL Lexer
To: Patrick LeBoutillier <[email protected]>,
[email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
This may be a better approach then my code. I didn't create a separate
parser/lexer.
-Keith
On Fri, May 8, 2009 at 9:53 PM, Patrick LeBoutillier
<[email protected]> wrote:
> Hi all,
>
> In the process of writing an SQL parser I started by writing a lexer.
> The code can be found here:
> http://hpaste.org/fastcgi/hpaste.fcgi/view?id=4736#a4736
>
> You can run it like this in ghci:
>
> Prelude SQL.Lexer> runLexer "select * from TABLE order by FIELD"
> [Token Reserved "select",Token Space " ",Token Operator "*",Token
> Space " ",Token Reserved "from",Token Space " ",Token Identifier
> "TABLE",Token Space " ",Token Reserved "order",Token Space " ",Token
> Reserved "by",Token Space " ",Token Identifier "FIELD"]
>
> Since this is pretty much my first Haskell project over 10 lines long,
> I'm looking for some feedback of any kind.
> Ultimately I would like to use this lexer to build a functional SQL
> parser using Parsec.
>
>
> Thanks,
>
> Patrick
>
> --
> =====================
> Patrick LeBoutillier
> Rosemère, Québec, Canada
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
Message: 4
Date: Sat, 09 May 2009 17:30:02 +0100
From: Magnus Therning <[email protected]>
Subject: Re: [Haskell-beginners] A Quantity Type - Integer without the
Negative #'s
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="utf-8"
Daniel Carrera wrote:
> Magnus Therning wrote:
>> aditya siram wrote:
>>> Hi all,
>>> Is there a datatype in Haskell that can be used to represent only
>>> quantities >= 0? I got bitten by a bug because I forgot to reject an
>>> amount that was below zero after applying a decrementing operator. A
>>> simple unit test would have caught this, but I was wondering if there
>>> was some way of getting the type system to ensure this.
>>
>> Maybe Word32 (or one of it's siblings) would do? It's basically the
>> same as 'unsigned int' in C, so it can under- and over-flow.
>
> What's under-flow?
Negative overflow:
> let one = 1 :: Word8
> one - 2
255
/M
--
Magnus Therning (OpenPGP: 0xAB4DFBA4)
magnusï¼ therningï¼org Jabber: magnusï¼ therningï¼org
http://therning.org/magnus identi.ca|twitter: magthe
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------------------------------
Message: 5
Date: Sat, 09 May 2009 17:50:33 +0100
From: Kevin Haines <[email protected]>
Subject: [Haskell-beginners] Performance of function defined in a
'where' clause
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi All,
I'm trying to write a bit of code that maps each byte in a block of
Word8's to 3xWord8 using an array; i.e. mapping from 8 bit to 24 bit
colour (this is an OpenGL application, and I'm using textures).
I should point out that this is experimental code, and I'm still
learning Haskell (and *loving* it, by the way!), so it probably looks a
little unpolished.
First, some data:
data Palette = Palette { palRed :: Word8, palGrn :: Word8, palBlu :: Word8 }
palette = listArray (0,49) paletteList
paletteList = [
Palette 0 0 0,
Palette 0 0 0,
Palette 0 0 0,
.....
Then, my first implementation, which took 57% time under profiling, was:
loadTile :: Int -> Int -> IO (Ptr Word8)
loadTile lat lon = do
terrainBytes <- readTile lat lon
-- implementation #1
mapM_ (paletteMapper terrainBytes rgbBytes) [0..tileSize^2-1]
free terrainBytes
return rgbBytes
where tileSize = 128
paletteMapper :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
paletteMapper tb rgb idx = do
v <- peekElemOff tb idx
pokeByteOff rgb (idx*3) (palRed (palette!v))
pokeByteOff rgb (idx*3+1) (palGrn (palette!v))
pokeByteOff rgb (idx*3+2) (palBlu (palette!v))
I tried moving paletterMapper out of the 'where' clause and into the
top level, which then took only 26% of time - i.e. half the time:
paletteMapper :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
paletteMapper tb rgb idx = do
v <- peekElemOff tb idx
pokeByteOff rgb (idx*3) (palRed (palette!v))
pokeByteOff rgb (idx*3+1) (palGrn (palette!v))
pokeByteOff rgb (idx*3+2) (palBlu (palette!v))
loadTile :: Int -> Int -> IO (Ptr Word8)
loadTile lat lon = do
terrainBytes <- readTile lat lon
-- implementation #1
mapM_ (paletteMapper terrainBytes rgbBytes) [0..tileSize^2-1]
free terrainBytes
return rgbBytes
where tileSize = 128
I don't understand why - the functions are the same, except for the
scope they're in. Can anyone elaborate on what's happening?
Incidentally, I now realise a faster way (14%) is:
loadTile :: Int -> Int -> IO (Ptr Word8)
loadTile lat lon = do
terrainBytes <- readTile lat lon
rgbBytes <- mallocBytes (3*(tileSize^2))
mapM_ (\x -> do
v <- peekElemOff terrainBytes x
pokeByteOff rgbBytes (x*3) (palRed (palette!v))
pokeByteOff rgbBytes (x*3+1) (palGrn (palette!v))
pokeByteOff rgbBytes (x*3+2) (palBlu (palette!v))
) [0..tileSize^2-1]
free terrainBytes
return rgbBytes
where tileSize = 128
(There may be faster/better ways still, I'm all ears :-)
Cheers
Kevin
------------------------------
Message: 6
Date: Sat, 9 May 2009 21:11:11 -0400
From: Brent Yorgey <[email protected]>
Subject: Re: [Haskell-beginners] Performance of function defined in a
'where' clause
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Sat, May 09, 2009 at 05:50:33PM +0100, Kevin Haines wrote:
>
> palette = listArray (0,49) paletteList
> paletteList = [
> Palette 0 0 0,
> Palette 0 0 0,
> Palette 0 0 0,
> .....
By the way, this should probably be something like
palette = listArray (0,49) (replicate 50 $ Palette 0 0 0)
Unless, of course, there are things other than Palette 0 0 0 in the
remainder of the list. If you ever have to copy and paste *anything*
in a Haskell program, warning bells should start going off in your
head. =)
Unfortunately, performance tuning is a black art of which I know
precious little. Perhaps others will have some good suggestions.
-Brent
------------------------------
Message: 7
Date: Sun, 10 May 2009 14:37:07 +1200
From: Andy Elvey <[email protected]>
Subject: Re: [Haskell-beginners] SQL Lexer
To: Patrick LeBoutillier <[email protected]>
Cc: beginners <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Patrick LeBoutillier wrote:
> Hi all,
>
> In the process of writing an SQL parser I started by writing a lexer.
> The code can be found here:
> http://hpaste.org/fastcgi/hpaste.fcgi/view?id=4736#a4736
>
> You can run it like this in ghci:
>
> Prelude SQL.Lexer> runLexer "select * from TABLE order by FIELD"
> [Token Reserved "select",Token Space " ",Token Operator "*",Token
> Space " ",Token Reserved "from",Token Space " ",Token Identifier
> "TABLE",Token Space " ",Token Reserved "order",Token Space " ",Token
> Reserved "by",Token Space " ",Token Identifier "FIELD"]
>
> Since this is pretty much my first Haskell project over 10 lines long,
> I'm looking for some feedback of any kind.
> Ultimately I would like to use this lexer to build a functional SQL
> parser using Parsec.
>
>
> Thanks,
>
> Patrick
>
>
Hi Patrick -
I like it! I'm still a Haskell beginner, but even to me, your code
seems very clear and easy to understand.
I've been thinking of doing some simple parsers too, so I was wondering
- may I use this code of yours as a base for them?
Well done, and thanks for doing this!
- Andy
------------------------------
Message: 8
Date: Sun, 10 May 2009 13:41:14 +0200
From: Peter Verswyvelen <[email protected]>
Subject: Re: [Haskell-beginners] Performance of function defined in a
'where' clause
To: Kevin Haines <[email protected]>
Cc: [email protected]
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Did you compile with -O or -O2?
On Sat, May 9, 2009 at 6:50 PM, Kevin Haines <[email protected]>wrote:
> Hi All,
>
> I'm trying to write a bit of code that maps each byte in a block of Word8's
> to 3xWord8 using an array; i.e. mapping from 8 bit to 24 bit colour (this is
> an OpenGL application, and I'm using textures).
>
> I should point out that this is experimental code, and I'm still learning
> Haskell (and *loving* it, by the way!), so it probably looks a little
> unpolished.
>
> First, some data:
>
> data Palette = Palette { palRed :: Word8, palGrn :: Word8, palBlu :: Word8
> }
>
> palette = listArray (0,49) paletteList
> paletteList = [
> Palette 0 0 0,
> Palette 0 0 0,
> Palette 0 0 0,
> .....
>
>
>
> Then, my first implementation, which took 57% time under profiling, was:
>
> loadTile :: Int -> Int -> IO (Ptr Word8)
> loadTile lat lon = do
> terrainBytes <- readTile lat lon
>
> -- implementation #1
> mapM_ (paletteMapper terrainBytes rgbBytes) [0..tileSize^2-1]
>
> free terrainBytes
> return rgbBytes
>
> where tileSize = 128
> paletteMapper :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
> paletteMapper tb rgb idx = do
> v <- peekElemOff tb idx
> pokeByteOff rgb (idx*3) (palRed (palette!v))
> pokeByteOff rgb (idx*3+1) (palGrn (palette!v))
> pokeByteOff rgb (idx*3+2) (palBlu (palette!v))
>
>
> I tried moving paletterMapper out of the 'where' clause and into the top
> level, which then took only 26% of time - i.e. half the time:
>
>
> paletteMapper :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
> paletteMapper tb rgb idx = do
> v <- peekElemOff tb idx
> pokeByteOff rgb (idx*3) (palRed (palette!v))
> pokeByteOff rgb (idx*3+1) (palGrn (palette!v))
> pokeByteOff rgb (idx*3+2) (palBlu (palette!v))
>
> loadTile :: Int -> Int -> IO (Ptr Word8)
> loadTile lat lon = do
> terrainBytes <- readTile lat lon
>
> -- implementation #1
> mapM_ (paletteMapper terrainBytes rgbBytes) [0..tileSize^2-1]
>
> free terrainBytes
> return rgbBytes
>
> where tileSize = 128
>
>
> I don't understand why - the functions are the same, except for the scope
> they're in. Can anyone elaborate on what's happening?
>
>
> Incidentally, I now realise a faster way (14%) is:
>
> loadTile :: Int -> Int -> IO (Ptr Word8)
> loadTile lat lon = do
>
> terrainBytes <- readTile lat lon
>
> rgbBytes <- mallocBytes (3*(tileSize^2))
> mapM_ (\x -> do
> v <- peekElemOff terrainBytes x
> pokeByteOff rgbBytes (x*3) (palRed (palette!v))
> pokeByteOff rgbBytes (x*3+1) (palGrn (palette!v))
> pokeByteOff rgbBytes (x*3+2) (palBlu (palette!v))
> ) [0..tileSize^2-1]
>
>
> free terrainBytes
> return rgbBytes
>
> where tileSize = 128
>
>
> (There may be faster/better ways still, I'm all ears :-)
>
> Cheers
>
> Kevin
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
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