- Haskell-Cafe - Haskell.org

Re: compiling hdirect
by Sigbjorn Finne 05 Feb '02

05 Feb '02

Johannes Goetx info(a)polirami.de writes: > ... > gcc -O -mno-cygwin -mwin32 -c mkNativeInfo.c -o mkNativeInfo.o > mkNativeInfo.c:0: malformed option `-D __WIN32__-DWIN32' ... > > malformed option `-D __WIN32__-DWIN32' > > Where can I change this? I could not find a file containing this > option string. Hi, you're using a version of gcc with a broken 'specs' file. Locate the specs file inside your cygwin(?) install tree & change the portion of the "*cpp:" section which expands -mwin32 and -mno-cygwin to the following: %{mwin32|mno-cygwin:-DWIN32 -D_WIN32 -D__WIN32 -D__WIN32__ -DWINNT } i.e., add a space after -DWINNT and the '}' This issue will soon go away, as the use of -mwin32 in GHC's fptools/ tree is in the process of being nuked. hth --sigbjorn

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Re: using composition with multiple argument functions
by Ashley Yakeley 03 Feb '02

03 Feb '02

[Moved to Cafe] At 2002-02-02 17:42, Dean Herington wrote: >With `h1 f g = f # g` and the type >declaration for h1, the compiler sees that f1 and g1 must be used at the >same type. With `h1 = f1 # g1`, that connection is missing. Yes. Haskell cannot be sure that the last instance declaration is the one it wants, because, even though it would work, there might be other possible instance declarations that could apply. Here's a simpler example: -- class C f where foo :: f -> Bool instance C (Bool->Bool) where foo f = f True instance C (Int->Int) where foo f = False f :: Bool f = foo id -- Either instance declaration would work, but Haskell needs one unambiguously for the general type of 'id'. You can fix it by restricting the type of 'id': -- f :: Bool f = foo (id :: Int -> Int) -- >So I guess my `Composable` class example can't work in general. Maybe, maybe not. -- Ashley Yakeley, Seattle WA

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compiling hdirect
by Johannes Goetz 02 Feb '02

02 Feb '02

Hi! Just tried to compile hdirect... ;-) $ make boot make -C src boot && make -C src all make[1]: Entering directory `/home/Administrator/fucker/hdirect/src' rm -f Version.hs echo "--Automatically generated" > Version.hs echo "module Version where" >> Version.hs echo "" >> Version.hs echo "pkg_name :: String" >> Version.hs echo "pkg_name = \"HaskellDirect (ihc.exe)\"" >> Version.hs echo "pkg_version :: String" >> Version.hs echo "pkg_version = \"snapshot 020202\"" >> Version.hs gcc -O -mno-cygwin -mwin32 -c mkNativeInfo.c -o mkNativeInfo.o mkNativeInfo.c:0: malformed option `-D __WIN32__-DWIN32' make[1]: *** [mkNativeInfo.o] Error 1 make[1]: Leaving directory `/home/Administrator/fucker/hdirect/src' make: *** [boot] Error 2 malformed option `-D __WIN32__-DWIN32' Where can I change this? I could not find a file containing this option string. Thanks, Johannes

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Re: functions not in type classes
by Yoann Padioleau 02 Feb '02

02 Feb '02

"Cagdas Ozgenc" <co19(a)cornell.edu> writes: > Greetings. > > Why does Haskell let you write functions that are not a part of type class? > For example instead of the goal of type class is to allow overloading of function, so for example id x = x is not subject to overloading => no use to put it in a type class. > > elem :: Eq a => a -> [a] -> Bool > map :: (a -> b) -> [a] -> [b] > > class Container a where > elem :: Eq b => b -> a b -> Bool > map :: (b -> c) -> a b -> a c > > would define methods that can work on all containers, and create a > discipline to write more reusable and generic functions. yes, that's right that map and elem could be put in a type class, but that's hard and require more advanced feature of haskell (here you use constructor class but you need more : multi-parameter class, ....) see http://www.cse.ogi.edu/~mpj/fds.html. > > Thanks > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Yoann Padioleau, INSA de Rennes, France, Opinions expressed here are only mine. Je n'écris qu'à titre personnel. **____ Get Free. Be Smart. Simply use Linux and Free Software. ____**

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monad thinking process
by Cagdas Ozgenc 25 Jan '02

25 Jan '02

Greetings. I have very little experience with monads. However my first impression is that there is too much thinking process involved in programming with monads, and it is very time consuming, at least for a beginner like myself. I don't know how productivity changes once you get used to programming with them. Also, I have serious concerns about the maintenance of programs written in monadic style. Since there is too much plannning overhead, it doesn't seem suitable for evolutionary software development process. What do monad experts think? What do you think of code readability? How easy is it to prove that programs written with monads are correct? How does changing one function affect other functions, in terms of maintenance? Thanks

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Re: Monad composition
by John Hughes 25 Jan '02

25 Jan '02

Andre W B Furtado wrote: >Well, it's also possible to interchange data between these two monads by: > >unsafeIOToST :: IO a -> ST s a >stToIO :: ST s a -> IO a > >Can anyone tell the possible problems related to >unsafeIOToST? >^^^^^^ Probably in the same manner as with unsafePerformIO: it can break referential transparency. Indeed, unsafePerformIO m = runST (unsafeIOToST m) so they're just as unsafe as each other. John Hughes

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Dynamic linking of Haskell modules?
by senganb＠ia.nsc.com 25 Jan '02

25 Jan '02

I'd like to be able to dynamically load Haskell code from a "plugin" binary file into a Haskell application, just as I can dynamically load .so files into a C application. Since ghci does this, I thought I could copy its implementation but after looking into it, it's very complicated. I notice that OCaml can do this (http://algol.prosalg.no/~malc/scaml/) The only simple solution I can think of is to use FFI to export the objects in the .so file as following the C interface, and then importing them into the main Haskell application as "C functions", but the extra marshalling is ugly. Has anyone solved this problem? Are there any plans to support this in the future in ghc or a third party library? Sengan

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Re: Monad composition
by Tom Bevan 24 Jan '02

24 Jan '02

Andre, I can't work out how it should be done. The way I see it, the StateIO monad should have four functions associated with it. 1/ update - a function to update the state 2/ retrieve - a function to retrieve the state from the monad These two are inherited from the standard State monad 3/ input - make a character from stndIn available to the state transformation functions 4/ output - send the state of the monad after a certain set of transformations to stndOut I've managed to write functions 1-3 but not 4. Here's my work so far.I'm not really sure if this is on the right track. Tom On Thu, 2002-01-24 at 14:32, Andre W B Furtado wrote: > Hi, I have the same problem. Did anyone answered your question? > > Thanks, > -- Andre > > ----- Original Message ----- > From: Tom Bevan <tom(a)regex.com.au> > To: Haskell Cafe List <haskell-cafe(a)haskell.org> > Sent: Wednesday, January 23, 2002 4:29 AM > Subject: Monad composition > > > > > > Hi all, > > > > I'm writing a programme which requires IO actions to be interleaved with > > operations on a State monad. From what I can work out, this means that > > the IO Monad and the StateTransformation monad need to be composed into > > a single highr order monad. > > Does anyone have any references or pointers on how this should be done? > > > > > > Tom > > > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

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Monad composition
by Tom Bevan 24 Jan '02

24 Jan '02

Hi all, I'm writing a programme which requires IO actions to be interleaved with operations on a State monad. From what I can work out, this means that the IO Monad and the StateTransformation monad need to be composed into a single highr order monad. Does anyone have any references or pointers on how this should be done? Tom

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Re: performance of monads
by John Hughes 24 Jan '02

24 Jan '02

I've felt need to use State monads in two distinct situations: ... And I've seen two distict aproaches. Using a State monad like one provided with GHC (1), or a state monad like the one defined in the paper "Moands for the Working Haskell Programmer" (2). In (1), I can see how I can take advantage of the monad and make updates in place using referencies. But then you'll have to either: - pass the referencies as a parameter to the functions where you use them (needless too say that this defeats the (my) main purpose of using a state monad which is in case A, keep track of data with minimal signature change ) You can do this conveniently using implicit parameters bound to your references: that way you don't have to add parameters to all your function definitions just to pass in a reference. (The types do change, though). I would probably use one implicit parameter bound to a record of references. ... Another state issue, sometimes I have some values that I want to keep constant through the whole algorithm. Example: (some very simple NNs for instance) - learning rate - activation function - maximum number of steps - minimum error required So I'll just declare them as 'constants'. But what if I decide I want the user to be able to chose? Now I got two options: - pass them around as values to all the functions - And signatures get HUGE - just pass them to a higher level function that will encapsulate the functions that use them... which is ugly and complicates everything because you can't test the lower level functions in the interpreter. Am I missing something here or is this really the best you can do? Implicit parameters solve this too. Read http://www.cse.ogi.edu/~mbs/pub/implicit_parameters/ I've written a short article on global variables in Haskell, which explains this particular application. http://www.md.chalmers.se/~rjmh/Globals.ps John Hughes

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