March 2003 - Haskell - Haskell.org

Re: Tutorial for literate Haskell
by b.i.mills＠massey.ac.nz 03 Mar '03

03 Mar '03

Yo, Steffen Mazanek wrote: > I do Literate Programming this way: > At first I define a Latex environment "code" as "verbatim" > e.g. so: \newenvironment{code}{\footnotesize\verbatim}{\endverbatim\normalsize} When I ran into the same question some time ago I tried that, but found that the \verbatim was interpreted to0 literally, so that the \end{code} does not terminate it. Could you give a complete short example that works for you? My own solution was to copy the definition of verbatim from the base files, and define code the same way in a separate style file. Regards, Bruce.

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looking for Database Interface in Haskell
by Johannes Waldmann 03 Mar '03

03 Mar '03

Dear all, we want to access a (MySQL) data base, running on a linux server, from a Haskell program. We planned to use http://www.volker-wysk.de/mysql-hs/ but it depends on earlier versions of hdirect (0.17?) and ghc(-4?). I built hdirect-0.19 (?) (from the ghc CVS) but the Foreign interfaces seem to have changed a bit since mysql-hs-0.10.1 was written. Any hints on what direction to take? Thanks, -- -- Johannes Waldmann ---- http://www.informatik.uni-leipzig.de/~joe/ -- -- joe(a)informatik.uni-leipzig.de -- phone/fax (+49) 341 9732 204/207 --

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Re: How to force UNIX text files as output instead of DOS text files??
by Alexandre Weffort Thenorio 03 Mar '03

03 Mar '03

Thanks a lot m8. I got it. I was supplying it with --make but not with -o. Thanks again. I guess everything is fine now thanks to you guys.I wanna learn more about catching errors but that comes later when I finish this program. Best Regards Alex ----- Original Message ----- From: "Nils Decker" <nils(a)ndecker.de> To: "Alexandre Weffort Thenorio" <alethenorio(a)home.se> Sent: Monday, March 03, 2003 7:19 PM Subject: Re: How to force UNIX text files as output instead of DOS text files?? > "Alexandre Weffort Thenorio" <alethenorio(a)home.se> wrote: > > Hi Great I got it working. Thanks a lot guys. My only problem now is > > when compiling. I am getting: > > > > hextodat.0(.text+0x34):fake: undefined reference to '_stginit_IOExts' > > > > Anybody can tell me what could be wrong?? I can run --make but when > > trying to compile with -o flag I get this error. > > AFAIK, you have to supply -package lang to the linker too when using seperate > compilation. > > > e.g: > ghc -package lang -o foo.o foo.hs > ghc -package lang -o foo foo.o ... > > Regards > Nils > > -- > Unix is user friendly - it's just picky about it's friends. > > Nils Decker <nils(a)ndecker.de> >

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RE: fundeps for extended Monad definition
by oleg＠pobox.com 03 Mar '03

03 Mar '03

| > The reason, which is thoroughly explained in Simon Peyton-Jones' | > message, is that the given type signature is wrong: it should read | > f1 :: (exists b. (C Int b) => Int -> b) > Can you give an example of its use? Yes, I can. > class (Show a, Show b) => C a b | a -> b where > doit:: a -> b -> String > instance C Int Int where > doit a b = (show a) > instance C Bool Bool where > doit a b = if a then "everything" else "nothing" > newtype M a = M (forall b.(C a b) => b) > f :: Int -> M Int > f x = M undefined > g :: Bool -> M Bool > g x = M undefined > test1 a = case (f a) of > M b -> doit a b > test2 a = case (g a) of > M b -> doit a b I wonder if the Obfuscated Haskell contest has an entry for the most useless type (with no uses). However, if a type can be used for the contest, it is no longer the most useless. This makes one wonder if the rules of the contest implicitly contain the Russel paradox.

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RE: fundeps for extended Monad definition
by Simon Peyton-Jones 03 Mar '03

03 Mar '03

| > The reason, which is thoroughly explained in Simon Peyton-Jones' | > message, is that the given type signature is wrong: it should read | > f1 :: (exists b. (C Int b) => Int -> b) | | Right. Simon pointed out that this is a pretty useless function, but not | entirely so, since the result of it is not of type 'forall b. b', but | rather of 'forall b. C Int b => b'. Thus, if the C class has a function | which takes a 'b' as an argument, then this value does have use. I disagree. Can you give an example of its use? Simon

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Persistent data
by Sengan.Baring-Gould＠nsc.com 03 Mar '03

03 Mar '03

Is there some way to reduce the cost of garbage collection over large persistent datastructures without resorting to escaping to C to malloc memory outside the heap? The program I'm working is part database, which cannot discard information. The net result is that I see figures like 82.9% of the time taken by garbage collection. The heap profile looks like a charging capacitor: a linear increase (as expected) which is slowly dilated as time increases by the garbage collector thrashing memory. When I worked on the LOLITA natural language processor we solved the problem by moving a lot of the data out to C++, so that the heap only contains things soon to be freed. I know generational garbage collection is supposed to help, but it doesn't seem to. Is there a pure Haskell solution to this problem? Sengan

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How to force UNIX text files as output instead of DOS text files??
by Alexandre Weffort Thenorio 03 Mar '03

03 Mar '03

I am working on a small program which writes a text file but I need this file to be in UNIX format and as it is a Windows program I am compiling it, the output file tends to be in DSO format. Is there anyway that I can force it to create the file in UNIX format??? Best Regards NooK

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AW: GUI for Windows
by Markus.Schnell＠infineon.com 03 Mar '03

03 Mar '03

Thanks, Axel, Daan, I will have a try with ObjectIO. (At least the examples work ;-)) Markus

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Tutorial for literate Haskell
by Daniel Luna 03 Mar '03

03 Mar '03

I am planning to write a small project in Haskell and stumbled upon some text that mentioned literate Haskell. Is there any good tutorial on how to write literate Haskell? I know that I could take any tutorial on latex and use that, but that's not what I am after. What I want is more like a base document with header and footer done, and perhaps a couple of example files. With that as a base I could get a hint on what the correct idioms for literate Haskell are. If there is no such tutorial a few hints on how other persons write would be very welcome. (with that I mean: how to comment (what info is relevant), how much/little one should describe a function/module, and such stuff) #Luna -- Daniel Luna | Top reasons that I have a beard: luna(a)update.uu.se | a) Laziness. http://www.update.uu.se/~luna/ | b) I can. Don't look at my homepage (it stinks).| c) I can get away with it.

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int to float problem
by Mike T. Machenry 03 Mar '03

03 Mar '03

Hello, I am having a problem. I recently desided I wanted a bunch function to return float instead of Int. I changed their type and wrote a new function that returned a float. I figured it'd be okay if all the others still returned Int since it's trivial to convert Int to Float. Sadly Haskell won't let me do this. What should I do? I attempted to cast all of the values in the functions that returned Int to Float, but I found no way to do this. I found fromInteger but it didn't seem to work on the return value of the cardinality function for instance. I guess cardinality much return Int. This is one of my functions. smallestSet :: GameState -> Float smallestSet s = (-1 * cardinality (fLocations s)) This function is an error because it infer's an Int. Thanks, -mike

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