RE: Calling Haskell from Python / C++
| So here is what I envision: I write the main | application in Python. I write a (hopefully) small | Haskell module that: | a) Calls back to the main Python app for reading the | text to be parsed, preferably using laziness. | b) Parses the text, and maybe processes a bit. | c) Returns the parsed data-structure. (This may be | tricky, but I think I know how to do it). If Python uses C's calling convention, it might be easy; just use 'foreign import' and 'foreign export' (see the FFI spec at haskell.org). If it doesn't, someone would have to add the Python calling convention to the various implementations. Simon ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Calling Haskell from Python / C++
Simon Peyton-Jones writes: If Python uses C's calling convention, it might be easy; just use 'foreign import' and 'foreign export' (see the FFI spec at haskell.org). I remember reading that the main program, that wants to call Haskell code, would have to be compiled with a special Haskell main() routine, though? Is that true? And if, why is that necessary? -peter ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: Record of STRefs better than STRef to a Record?
If I use an STRef to a record, will a new record be created
each time I want
to update a single field? Or can I expect GHC to optimize it
and have the field of the record updated in place?
You'll get a new record for each update. This might not be so bad
though, depending on the number of fields in your record.
Right now I'm using a record of STRefs, like:
data E s = E{
refi :: STRef s Int,
refc :: STRef s Char
}
but it can get a little messy, since thread s propagates to
every datatype that uses the record type in it's definition.
Here's another trick if you use this route:
data E s = E{
refi :: !STRef s Int,
refc :: !STRef s Char
}
and compile with -funbox-strict-fields. This will eliminate the boxing
of the STRefs.
Cheers,
Simon
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Re: 1 line simple cat in Haskell
main = mapM (=putChar) getCharS where getCharS = getChar:getCharS
How would you suggest to neatly insert the error handling code into ?
\begin{code}
-- some suggestions for a little zoo of cats
module Main where
import IO
import Monad
main0 = interact id
main1 = getContents = putStr
main2 = untilEOF (getChar=putChar)
catchEOF io = catch io (\e-unless (IO.isEOFError e) (ioError e))
untilEOF io = catchEOF (sequence_ $ repeat io)
main = main2
\end{code}
Claus
PS. I haven't kept up to date with buffering issues,
and hugs/ghci may not like this kind of code..
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RE: Calling Haskell from Python / C++
--- Simon Peyton-Jones [EMAIL PROTECTED] wrote: | So here is what I envision: I write the main | application in Python. I write a (hopefully) small | Haskell module that: | a) Calls back to the main Python app for reading the | text to be parsed, preferably using laziness. | b) Parses the text, and maybe processes a bit. | c) Returns the parsed data-structure. (This may be | tricky, but I think I know how to do it). If Python uses C's calling convention, it might be easy; just use 'foreign import' and 'foreign export' (see the FFI spec at haskell.org). If it doesn't, someone would have to add the Python calling convention to the various implementations. Unfortunately, Python does not support calling arbitrary C functions. In order to call C functions from Python, you have to write a Python extension module. (This restriction is actually a direct result of Python being interpreted, rather than compiled.) But I do have another idea: If I was working only on Windows, I could have used HaskellDirect to wrap the Haskell code as a COM component, and since Python seems to have good COM support (though I never used it) this would have solved my problem neatly. However, I need Linux portability, which rules out using COM. But there is a good COM alternative for Linux: XPCOM from the Mozilla project. This is a cross-platform and somewhat improved COM, which has C++, Java, JavaScript, Perl, and Python bindings. And this brings me to my next question: How difficult would it be to extend HaskellDirect to support XPCOM? Thanks, -JH __ Do you Yahoo!? U2 on LAUNCH - Exclusive greatest hits videos http://launch.yahoo.com/u2 ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
monadic stack to register machine translator
module GT where import Monad import Monoid import MonadState import MonadWriter import MonadRWS -- Just a quick exercise in using monads. -- Thought it'd be nice to share with the class. data GOp = PushVal Integer | Push Integer | Pop Integer | Slide Integer | Update Integer | GAdd | GSub | GMul | GDiv | GMod | GPow | GNeg | GAbs deriving (Eq, Ord, Read, Show) type Tmp = Integer data ROp = LoadImm Tmp Integer | RAdd Tmp Tmp Tmp | RSub Tmp Tmp Tmp | RMul Tmp Tmp Tmp | RDiv Tmp Tmp Tmp | RMod Tmp Tmp Tmp | RPow Tmp Tmp Tmp | RNeg Tmp Tmp | RAbs Tmp Tmp deriving (Eq, Ord, Read, Show) type CounterT m t = StateT Integer m t type StackT t = State [Integer] t type GST t = RWS () [ROp] (Integer, [Integer]) t class Stack f where pushVal, push, pop, update, slide :: Integral t = t - f () popVal :: Integral t = f t instance Integral t = Stack (RWS () [ROp] (t, [t])) where pushVal n = do (ctr, stk) - get put (ctr, fromIntegral n : stk) popVal = do (ctr, top:stk) - get put (ctr, stk) return (fromIntegral top) push n = do (ctr, stk) - get put (ctr, stk!!fromIntegral n : stk) pop n = do (ctr, stk) - get put (ctr, drop (fromIntegral n) stk) slide n = do (ctr, top:stk) - get put (ctr, top : drop (fromIntegral n) stk) update n = do (ctr, top:stk) - get let (front, _:back) = splitAt (fromIntegral n) stk put (ctr, front ++ [top] ++ back) class Counter f where gen :: Enum t = f t instance Integral t = Counter (RWS () [ROp] (t, [t])) where gen = do (ctr, stk) - get put (ctr + 1, stk) return . toEnum . fromIntegral $ ctr + 1 instance (Enum t, Monad m) = Counter (StateT t m) where gen = do ctr - get put $ succ ctr ctr - get return . toEnum $ fromEnum ctr translate gOps = snd $ evalRWS (mapM trans gOps) () (0,[]) trans :: GOp - GST () trans i = case i of PushVal n - do reg - gen tell [LoadImm reg n] pushVal reg Push n - push n Pop n - pop n Slide n - slide n Update n- update n GAdd- doBinOp RAdd GSub- doBinOp RSub GMul- doBinOp RMul GDiv- doBinOp RDiv GMod- doBinOp RMod GPow- doBinOp RPow GNeg- doUnOp RNeg GAbs- doUnOp RAbs where doUnOp op = do x - popVal y - gen tell [op y x] pushVal y doBinOp op = do x - popVal y - popVal z - gen tell [op z x y] pushVal z ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: 1 line simple cat in Haskell
I'm not sure why someone hasn't suggested
main = interact id
which I think would accomplis everything you want, and probably be a heck
of a lot faster, as (apparently) putChar and getChar are quire
inefficient.
--
Hal Daume III
Computer science is no more about computers| [EMAIL PROTECTED]
than astronomy is about telescopes. -Dijkstra | www.isi.edu/~hdaume
On Wed, 13 Nov 2002, William Lee Irwin III wrote:
On Wed, Nov 13, 2002 at 03:29:53PM +0900, Ahn Ki-yung wrote:
If you are steaming with compicated codes, then how about taking a break.
Let's play with a simple cat.
\begin{code}
main = mapM (=putChar) getCharS where getCharS = getChar:getCharS
\end{code}
Why not this?
main = mapM_ (\h - mapM_ putChar = hGetContents h) = mapM (flip openFile $
ReadMode) = getArgs
Bill
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Re: Record of STRefs better than STRef to a Record?
If I use an STRef to a record, will a new record be created
each time I want
to update a single field? Or can I expect GHC to optimize it
and have the field of the record updated in place?
You'll get a new record for each update. This might not be so bad
though, depending on the number of fields in your record.
One of them has 4, the other 3, but they might grow bigger...
Here's another trick if you use this route:
added some parenthesis
data E s = E{
refi :: !(STRef s Int),
refc :: !(STRef s Char)
}
and compile with -funbox-strict-fields. This will eliminate the boxing
of the STRefs.
Nice, thanks :)
One more question.
I'm passing that 'record' around as an implicit value. The record as STRefs
that I use to collect info, but it also has some pure fields with 'read-only'
info. Something like,
data E s = E{
refi :: STRef s Int,
refc :: STRef s Char,
max :: Int
}
In some functions I might need only some pure fields, and none of the STRefs,
but since I pass something of type 'E s' around, everything ends up beeing
monadic. Is using two records (on with STRefs and one with pure fields) the
only/best way to avoid this?
I would like to use two records, doesn't seem natural, but I also don't like
to end up using monadic functions when they are, in fact, pure...
Thanks,
J.A.
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Re: 1 line simple cat in Haskell
On Wed, 13 Nov 2002, William Lee Irwin III wrote: main = mapM_ (\h - mapM_ putChar = hGetContents h) = mapM (flip openFile $ ReadMode) = getArgs On Wed, Nov 13, 2002 at 07:46:41AM -0800, Hal Daume III wrote: main = interact id There is a semantic difference here, as the version I posted above takes files from the command-line, though it does fail to accommodate the pass-through case, which is handled by: main = getArgs = \args -if args == [] then interact id else mapM readFile args = mapM_ putStr .. which seems to be a bit above 80 chars. Some library function trickery is probably in order to cut the if statement down to size. e.g. nonEmptyMapM_ :: Monad m = m () - (t - m ()) - [t] - m () nonEmptyMapM_ def _ [] = def nonEmptyMapM_ _ f xs@(_:_) = mapM_ f xs main = getArgs = nonEmptyMapM_ (interact id) ((= putStr) . readFile) Bill ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
