[Haskell-cafe] Re: Matching constructors
Mark T.B. Carroll wrote: Creighton Hogg [EMAIL PROTECTED] writes: data Patootie = Pa Int | Tootie Int and I want to pull out the indices of all elements of a list that have type constructor Tootie, how would I do that? x = [Pa 3, Tootie 5, Pa 7, Tootie 9, Pa 11] y = [ i |Tootie i - x ] z = [ i | i@(Tootie _) - x ] I think this is what the OP wanted: [ i | (i,Tootie _) - zip [0..] x ] -- Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Digrams
I've quickly put this together to measure frequencies of pairs of letters
(e.g. 1st and 2nd) in words. It works fine on a small test data sets but I
have a feeling that it will perform poorly as it spends a lot of time
updating a 26*26 array. Before I throw a dictionary at it, does anyone have
any suggestions?
Thanks, Dominic.
import System.IO
import Data.Char
import Data.Array
import Data.List
main =
do h - openFile girls2005.txt ReadMode
c - hGetContents h
let freqs1 = g 1 2 (lines c) digramArr
xs = map putStrLn .
map show .
reverse .
sort .
map Cell .
assocs $ freqs1
sequence_ xs
putStrLn Finished
newtype Cell = Cell ((Char,Char),Int)
deriving Eq
instance Ord Cell where
Cell (_,i) = Cell (_,j) = i = j
instance Show Cell where
show (Cell ((i,j),f)) = i : ',' : j : ',' : show f
letters = ['A'..'Z']
digramElems = [((i,j),0) | i - letters, j - letters]
digramArr = array (('A','A'),('Z','Z')) digramElems
f n m s a =
a // [((i,j),x+1)]
where i = toUpper (s!!(n-1))
j = toUpper (s!!(m-1))
x = a!(i,j)
g n m [] a = a
g n m (s:ss) a = g n m ss (f n m s a)
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Re: [Haskell-cafe] Digrams
On Saturday 11 Feb 2006 1:09 pm, Jon Fairbairn wrote:
On 2006-02-11 at 12:25GMT Dominic Steinitz wrote:
I've quickly put this together to measure frequencies of pairs of letters
(e.g. 1st and 2nd) in words. It works fine on a small test data sets but
I have a feeling that it will perform poorly as it spends a lot of time
updating a 26*26 array. Before I throw a dictionary at it, does anyone
have any suggestions?
I think this is the sort of thing for which accumArray was
invented.
Jon, Much better. Thanks, Dominic.
import System.IO
import Data.Char
import Data.Array
import Data.List
main =
do h - openFile girls2005.txt ReadMode
c - hGetContents h
let xs = map putStrLn .
map show .
reverse .
sort .
map Cell .
assocs $ f 1 2 (lines c)
sequence_ xs
putStrLn Finished
newtype Cell = Cell ((Char,Char),Int)
deriving Eq
instance Ord Cell where
Cell (_,i) = Cell (_,j) = i = j
instance Show Cell where
show (Cell ((i,j),f)) = i : ',' : j : ',' : show f
hit m n l =
(toUpper (l!!(m-1)), toUpper (l!!(n-1)))
f m n c =
accumArray (+) 0 (('A','A'),('Z','Z')) [(hit m n l,1) | l - c]___
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Re: [Haskell-cafe] Re[2]: strict Haskell dialect
Bulat Ziganshin wrote:
Hello Wolfgang,
Saturday, February 11, 2006, 3:17:12 PM, you wrote:
each and every monadic operation is a function!
WJ What do you mean with monadic operatation? (=), () and return are, of
WJ course, functions but an I/O action like getChar is *not* a function. Also a
WJ list is not a function but a value of the list monad.
type IO a is really RealWorld - (RealWorld,a)
WJ This representation is just there to help people understand what I/O is but
WJ actually, IO a is a type which is not implementable in ordinary Haskell and
WJ therefore cannot be a function. In addition, RealWorld - (RealWorld,a) as
WJ an explanation of what IO a is has its limitations. If we run an I/O action,
WJ we aren't just interested in the final state but also in intermediate states.
{putStr a} is a function, which receives previous world state and
returns updated world state where a is written to the terminal. it's
an _essential_ part of monadic way to I/O
There is nothing in the Haskell specification that tells you how the
IO type is implemented, so you can't say that putStr takes an old
world state and returns a new one. I've personally done an
implementation that was totally different, so making assumptions
about how IO is implemented is just wrong.
-- Lennart
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[Haskell-cafe] Haskell XSLT interpreter?
Has anyone written a pure haskell xslt interpreter? If not, how difficult would it be to do so? -Alex- __ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell XSLT interpreter?
Hi, I don't know of any, but there may well be, I've never looked. It probably wouldn't be that difficult to do, since XSLT is a functional language. There is probably lots of code in HaXml you could reuse (since the syntax for XSLT is XML). The only slightly taxing thing would be that XSLT is not pure (see the document function), so you may have to put most of it in the IO Monad. This would be very handy since Yhc uses XSLT to do some stuff (for example, http://www-users.cs.york.ac.uk/~ndm/yhc/bytecodes.html) and currently the choices seem to be MSXSL (which is great for me on Windows, but sucks a bit for others), or Xalan which is very slow. Having a Haskell XSLT is something I considered doing before, but never got round to... Thanks Neil On 11/02/06, S. Alexander Jacobson [EMAIL PROTECTED] wrote: Has anyone written a pure haskell xslt interpreter? If not, how difficult would it be to do so? -Alex- __ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell XSLT interpreter?
Neil == Neil Mitchell [EMAIL PROTECTED] writes: Neil Hi, I don't know of any, but there may well be, I've never Neil looked. Neil It probably wouldn't be that difficult to do, since XSLT is Neil a functional language. There is probably lots of code in Neil HaXml you could reuse (since the syntax for XSLT is Neil XML). The only slightly taxing thing would be that XSLT is Neil not pure (see the document function), so you may have to put Neil most of it in the IO Monad. In what way is the document() function not pure? In XSLT 2.0 at least, it is defined in such a way that it can be implemented as a pure function. That is, the static context is defined to include a mapping from URIs to document nodes, and document() returns those document nodes that it's argument nodes map to. -- Colin Adams Preston Lancashire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Badly designed Parsec combinators?
So... I see no reason why someone can't just do it themselves, but...
I was playing around with Parsec (as included in GHC 6.4.1), and I found
two functions that are... not quite what I believe they should be.
optional :: GenParser tok st a - GenParser tok st ()
optional p = do{ p; return ()} | return ()
Now, this completely loses the result of the optional parser. Better
would be:
optional :: GenParser tok st a - GenParser tok st (Maybe a)
optional p = do{ x - p; return (Just x) } | return Nothing
Same thing with manyTill:
manyTill :: GenParser tok st a - GenParser tok st end - GenParser tok
st [a]
manyTill p end = scan
where
scan = do{ end; return [] }
|
do{ x - p; xs - scan; return (x:xs) }
Better:
manyTill :: GenParser tok st a - GenParser tok st end - GenParser tok
st ([a], end)
manyTill p end = scan
where
scan = do{ endr - end; return ([], endr) }
|
do{ x - p; (xs, endr) - scan; return (x:xs,
endr) }
Is there any reason I can't see why they are the way they are?
JCAB
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[Haskell-cafe] building ghc on win with gcc of cygwin, without cygwin1.dll (-mno-cygwin flag) ?
Hi.. I've found the nice documentation about building ghc on haskell.org/ghc - documentation. There is one chapter (#1) about C compilers and environments to use: Either MSYS or cywin and gcc of MinGW because gcc of cygwin will link to cygwin1.dll by default which may change and therefore can brake your apps. Googling around I've found that there exists the -mno-cygwin flag which you can use to not include this lib.. So would it might be possible to get a ghc build not using cygwin.dll with just cygwin ? I haven't read anything about that in those docs. Or does this flag simply include cygwin.dll within your apps (statically linked) ? #1 :http://www.haskell.org/ghc/docs/latest/html/building/platforms.html#ghc-cygwin Marc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
