- Haskell-Cafe - Haskell.org

Re: URGENT: File exists
by Richard Uhtenwoldt 03 Nov '01

03 Nov '01

bracaman(a)box.sk writes: >I am trying to emulate bash in haskell, and i got a function called shell that waits fot the command and then executes it. The problem is that if the file does not exist, the program returns to Main (it gets out of the shell). The only thing i want to do is to return to the shell after an IOError. > >How can i perform such a thing? You could test if the file exists, like you said before, but that test would fail once in a while, when another process deletes the file after your test but before the file is opened. This is called a "race condition" and should be avoided when possible. The best thing is to use catch which has the type IO a -> (IOError -> IO a) -> IO a. An example (untested code) is catch (do hdl<-openFile "/home/bracaman/foo" ReadMode char<-hGetChar hdl string<-hGetLine hdl ) --we caught an exception: (\errorCode-> if isDoesNotExistError errorCode then "return to shell" else if isPermissionError errorCode then "return to shell" else --something strange happened. --re-raise the exception, which will probably return control to Main. ioError errorCode ) P.S. Instead of (do hdl<-openFile "/home/bracaman/foo" ReadMode char<-hGetChar hdl string<-hGetLine hdl ... ) you could have (do fileContentsAsABigString<-readFile "/home/bracaman/foo" ... ) but I try to stay away from readFile and getContents because they're not referentially transparent.

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Evolution of a Haskell Programmer
by Dmitry Astapov 01 Nov '01

01 Nov '01

It's a pity that such a link is not mentioned in "Haskell Bookshelf" :) http://www.willamette.edu/~fruehr/haskell/evolution.html -- Dmitry Astapov //ADEpt E-mail: adept(a)umc.com.ua GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D

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HaXml, emeory usage and segmentation fault
by Dmitry Astapov 01 Nov '01

01 Nov '01

I have Hugs version February 2001, HaXml version 1.02 and this program: > module Main where > import XmlLib > > main = processXmlWith (invoices `o` tag "invoice") > > invoices = > html > [ hhead > [ htitle [ ("Invoices"!)] ], > hbody > [ customers `o` children `with` tag "customer" ] > ] > > customers = > cat > [ h2 [ ("Customer"!) ], > contracts `o` children `with` tag "contract" > ] > > contracts = > cat > [ h3 [ ("Id:"!), ("id"?)], > hpara [ ("Access:"!), keep /> txt ] `o` children `with` tag "access", > hpara [ ("Intl:"!), keep /> txt] `o` children `with` tag "inter" > ] This program can process following file: <?xml version='1.0'?> <invoice> <customer> <contract id='1'> <access>1</access> <inter>1</inter> </contract> <contract id='2'> <access>2</access> <inter>2</inter> </contract> </customer> </invoice> (I use "runhugs translate.hs invoice.xml invoice.html") Now increase amount of <customer>s to 10, and amount of <contract>s within each customer to 999. After that, "runhugs -h6000000 translate.hs invoice.xml invoice.html" dumps core :( What's the reason: bug in hugs, bug in HaXml, or my own bad programming techniques? -- Dmitry Astapov //ADEpt E-mail: adept(a)umc.com.ua GPG KeyID/fprint: F5D7639D/CA36 E6C4 815D 434D 0498 2B08 7867 4860 F5D7 639D

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how to store new values in variables?
by Anders Elfgren 31 Oct '01

31 Oct '01

Hi, its me with the dungeon master-game again.. I'm in the process of making me able to move around, which I have succeeded with. Kind of. Remember the map type Pic = [[Char]] maplevel1 = ["##############", "# #", "### #", "# #", "# # #", "#P# #", "# #m #", "##############"] Now, I've made a function called s (for south) which just moves the 'P' one step down. It looks like this s :: Pic s = remap (findPos 'P' 1) (0,1) 1 findPos just finds the positin of the P, and 0,1 tells remap to move it one step on the y-axis. The remap function looks overly complicated right now so I'm not gonna put it in here, nad I dont think it really matters. What I want to do tho, is something like this s :: Pic s = maplevel1 <- (remap (findPos 'P' 1) (0,1) 1) so that it not only returns the new Pic, but also sets the maplevel1 variable to look like it should after the move. If I do putStr (unlines s) twice, it should move down two steps.. but it doesnt. We didn't learn this, well I didn't :), in the Haskell course so if someone can just give me an example of how I should do it it'd be nice.. Thanks again. The dm2.hs can be downloaded from www.dtek.chalmers.se/~srekel/ptf and yes, the draw2 function works :) ------------------------------------------------------------------------- Anders Elfgren || AKA: Srekel and Farfar Homepage: http://hem.passagen.se/srekel || Alt email: srekel(a)icqmail.com ICQ: 4596105 || AIM: Srekel - Kaka e gott || - Cs e halva mitt liv -------------------------------------------------------------------------

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Some more news about DM-haskell..
by Anders Elfgren 31 Oct '01

31 Oct '01

Hehe sure :) If I DO finish it that is :) It should actually be close to being at the state where I just have to add different images and when to display them. Then I need to work on some kind of function to allow it to take 'w','s','n'and 'e' as input, or if I can, the arrow keys. Btw, I see that when I hit reply in Pine I only send to the person that sent me the mail, not the whole list, so I'm going to make an alias for it. For those of you that don't know, I've managed to find the problem with the help of some fellow members of this list :) On Tue, 30 Oct 2001, Andre W B Furtado wrote: > Will you release your game when it is done? It seems very interesting and I > woud like to check how it will look like... > > -- Andre PS. Andre, there's a.. um.. game I guess, for Linux called Text-mode Quake. Search for it on www.google.com and you should find something interesting :D ------------------------------------------------------------------------- Anders Elfgren || AKA: Srekel and Farfar Homepage: http://hem.passagen.se/srekel || Alt email: srekel(a)icqmail.com ICQ: 4596105 || AIM: Srekel - Kaka e gott || - Cs e halva mitt liv -------------------------------------------------------------------------

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What does this error message mean
by Anders Elfgren 31 Oct '01

31 Oct '01

Short intro (skip down for the real reason for this email) : Hi, I'm a student at Chalmers and have finished the Haskell course but actually (is IS weird, but I'm pretty sure I like it... :) ) found the language to be pretty cool and decided to try and make an ascii-based Dungeon Master type game. For anyone who doesn't know what that is : Its a game in which you walk in a dungeon with corridors in a firstperson view. These are pictures that show what it looks like when you are looking down a corridor that turns right two and respectively one "moves" ahead of the current position. (Yes, I plan to make these better looking :) ) corrl_2 = ["##############", "# \\ / #", "# \\ ____ / #", "# | } #", "# |____} #", "# / \\ #", "# / \\ #", "##############"] corrl_1 = ["##############", "# \\ / #", "# \\ ______| #", "# | | #", "# |______| #", "# / | #", "# / \\ #", "##############"] This is the whole program. draw simply prints out all three pictures (including the overhead map found below) My (current) problem lies in whatPic, which returns the error Program error: {whatPic Facing2_North (1,6)} if I type in whatPic North (1,6) or just call it through the draw2 function (which is supposed to be the main drawing function, and it actually works.. Well it did yesterday until I did something :D (sorry about pine wrapping the lines.. if you're in luck you wont notice it.) import Observe draw = putStr ((unlines corrl_2) ++ (unlines corrl_1) ++ (unlines maplevel1)) data Facing2 = North | South draw2 = putStr (unlines (whatPic North (findPos 'P' 1))) findPos :: Char -> Int -> (Int,Int) findPos obj location | head (drop (location) (unlines maplevel1)) == obj = (location `div` 14,location `mod` 15) | otherwise = findPos obj (location + 1) whatPic :: Facing2 -> (Int,Int) -> Pic whatPic facin (x,y) | corridorType facin (x,y) == (2, "rTurn1") = corrl_1 | corridorType facin (x,y) == (2, "rTurn2") = corrl_2 corridorType :: Facing2 -> (Int,Int) -> (Int, String) corridorType facing (x,y) | observe "distWall" distWall facing (x,y) (x,y) == 4 && (whatIs (findPos 'P' 1) (1,-2) == ' ') = (2, "rTurn") | otherwise = (2, "rTurn") distWall :: Facing2 -> (Int,Int) -> (Int,Int) -> Int distWall North (x,y) (newx,newy) | whatIs (x,y) (x,y-1) == '#' = abs (y - newy) | whatIs (x,y) (x,y-1) == ' ' = distWall North (x,y) (x,y-1) --distWall (North) (x,y) (newx,newy) = 2 --distWall (South) (x,y) (newx,newy) = 2 whatIs :: (Int,Int) -> (Int,Int) -> Char whatIs (x,y) (xdiff,ydiff) = head (drop (x + xdiff + y + ydiff ) (unlines maplevel1)) --[1,2,3,4,5] type Pic = [[Char]] maplevel1 = ["##############", "# #", "### #", "# #", "# # #", "# # #", "#P#m #", "##############"] corrl_2 :: Pic corrl_2 = ["##############", "# \\ / #", "# \\ ____ / #", "# | } #", "# |____} #", "# / \\ #", "# / \\ #", "##############"] corrl_1 = ["##############", "# \\ / #", "# \\ ______| #", "# | | #", "# |______| #", "# / | #", "# / \\ #", "##############"] I'm sure its something simple.. I just can't make out what could be wrong right now. Thanks for any replies :) ------------------------------------------------------------------------- Anders Elfgren || AKA: Srekel and Farfar Homepage: http://hem.passagen.se/srekel || Alt email: srekel(a)icqmail.com ICQ: 4596105 || AIM: Srekel - Kaka e gott || - Cs e halva mitt liv -------------------------------------------------------------------------

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Vim syntax files for .lhs files using \begin{code} and \end{code}
by Nicholas Nethercote 30 Oct '01

30 Oct '01

Hi, The Vim syntax file for literate Haskell programs handles code lines that begin with a '>' character fine. But in GHC much of the code is defined between "\begin{code}" and "\end{code}" pairs, and that shows up as one giant comment. Does anybody know where I might be able to obtain a Vim syntax file that handles these constructs? I made a feeble attempt myself, but Vim's syntax highlighting language defeated me. Thanks. -- Nick Nethercote njn25(a)cam.ac.uk

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Re: HaXml, memory usage and segmentation fault
by Marcin 'Qrczak' Kowalczyk 27 Oct '01

27 Oct '01

27 Oct 2001 01:44:50 +0300, Dmitry Astapov <adept(a)umc.com.ua> pisze: > well, ghc-5.02 seems to dislike something inside XmlLib.hs - it > could not find interface defs file for modules IOExts .. Perhaps the option -package lang would help. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Project: creating a table using haskell
by MR NICHOLAS EDWARD SUTCH 22 Oct '01

22 Oct '01

To whome it may concern, I am currently involved in project using haskell to create a sample time table for a company. I am a newcomer to haskell and would like some help with creating an table for such a project which will print to screen. The data contained needs to be accessible in that I can take a location or a particular time from the table and individually print this to screen. Can anyone help? N. Sutch

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RE: ghci
by Simon Marlow 22 Oct '01

22 Oct '01

> The following code works fine under ghc, but produces a strange error > under ghci: > > Main> main > *** Exception: failed > Action: connect > Reason: Unknown error 141312000 > > It is deterministic - i.e I have verified that it isn't a network > fault. I'm afraid there's a bug in 5.02's SocketPrim library that causes this. The fix will be in 5.02.1, due out shortly (or pull it from CVS if you're brave :-). > Additionally, I'm a little confused about how to > import the PortNumber constructor from Socket, without > importing everything else. It's behavior seems odd. There isn't a PortNumber constructor, just a type constructor - is that what you meant? If so, doesn't just "import Socket(PortNumber)" do the right thing? Cheers, Simon

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