October 2003 - Hugs-Bugs

Fwd: when is defaulting supposed to occur?
by Mark Tullsen 31 Oct '03

31 Oct '03

So, it looks like it is hugs which is not following the report (section 4.5.5 (rule 2) as Iavor noted), which seems to indicate that defaulting only occurs after an entire module is type-checked. - Mark Begin forwarded message: > From: "Iavor S. Diatchki" <diatchki(a)cse.ogi.edu> > Date: Thu Oct 23, 2003 3:07:45 PM US/Pacific > To: Mark Tullsen <tullsen(a)galois.com> > Cc: haskell(a)haskell.org > Subject: Re: when is defaulting supposed to occur? > > hello, > the problem has to do with the monomorphism restriction > see section 4.5.5 (rule 2) (or typing hashell in haskell section > 11.5.1 for details). > bye > iavor > > > Mark Tullsen wrote: > >> Note the following program >> x = 1 >> y = x :: Int >> >> This is accepted by ghc but it is rejected hugs (May 2003 cvs): >> ERROR "IntegerTest.hs":4 - Type error in type annotation >> *** Term : x >> *** Type : Integer >> *** Does not match : Int >> >> My guess is that hugs is doing defaulting after a "declaration group" >> is type-checked, but that ghci leaves 'x' with type 'Num a', then >> processes further declaration groups, and then does defaulting. >> >> I don't see that the report specifies this (did I miss it?). >> >> - Mark >> >> >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell > > > > -- > ================================================== > | Iavor S. Diatchki, Ph.D. student | | Department of > Computer Science and Engineering | > | School of OGI at OHSU | > | http://www.cse.ogi.edu/~diatchki | > ================================================== >

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type checking LazyST
by Iavor S. Diatchki 30 Oct '03

30 Oct '03

hello, hugs seems to have trouble type checking the following program. it seems to work if i import ST rather than LazyST. it also works with ghci. > module Test where > import LazyST > f :: ST RealWorld (STRef RealWorld ()) > f = newSTRef () the error i get is: ERROR "test.lhs":9 - Type error in explicitly typed binding *** Term : f *** Type : ST a (STRef a ()) *** Does not match : ST RealWorld (STRef RealWorld ()) bye iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ==================================================

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INTERNAL ERROR: parseInput
by Henk-Jan.van.Tuyl 26 Oct '03

26 Oct '03

L.S., The attached program leads to the message: INTERNAL ERROR: parseInput at load time. I am running Hugs Version Nov 2002 on a Windows 98 system. Best regards, Henk-Jan van Tuyl --

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Re: Calling an external command from a Haskell program
by C.Reinke 21 Oct '03

21 Oct '03

> The function system works fine in Hugs except on windows where DOS limitations > cause the function to always return ExitSuccess. (ghc suffers from the same > problem on Windows.) Actually, that is not quite correct: ghc seems to suffer from this problem only on older Windows versions (such as Windows 98), whereas Hugs seems to have the bug also on newer Windows versions (such as XP), at least in its current binary release.. I reported the ghc/win98 problem earlier, below is what happens on Windows XP. So the bug seems even worse in Hugs than in GHC? Claus PS. why the differences in default access to standard modules? should GHC be more restrictive there? --------------------------------------------------- ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.0.1, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Prelude> System.system "fail" >>= print 'fail' is not recognized as an internal or external command, operable program or batch file. ExitFailure 1 Prelude> --------------------------------------------------- || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-2002 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs(a)haskell.org || || Version: Nov 2002 _________________________________________ Haskell 98 mode: Restart with command line option -98 to enable extensions Reading file "C:\Program Files\Hugs98\lib\Prelude.hs": Hugs session for: C:\Program Files\Hugs98\lib\Prelude.hs Type :? for help Prelude> :a System Reading file "C:\Program Files\Hugs98\lib\System.hs": Hugs session for: C:\Program Files\Hugs98\lib\Prelude.hs C:\Program Files\Hugs98\lib\System.hs System> system "fail" >>= print 'fail' is not recognized as an internal or external command, operable program or batch file. ExitSuccess

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None
by Doug McIlroy 16 Oct '03

16 Oct '03

In Hugs 1.4, ++ was an operator of class Monad; in Hugs 98 it is an operator on lists. I've looked in the Hugs documentation and haven't found anything about the change (probably a failing of mine, not the documentation). Anyway, that breaks some code in an article that's been accepted for JFP, wherein I overloaded ++ by placing the operand type in class Monad. This doesn't work any more. I don't want to publish code that doesn't work, and I don't want to give up that overloading, which is completely natural. Can you shed any light on what happened between the two versions? Or offer an idea about how to rescue the overloading? Many thanks, Doug McIlroy

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Type error for function main
by Josef Svenningsson 16 Oct '03

16 Oct '03

Hi! I was just trying to write the smallest valid Haskell program. One try was the following: > main = return 0 But I get the following error message: ERROR "foo.hs":1 - Unresolved top-level overloading *** Binding : main *** Outstanding context : Monad c Why do I get this? According to the Haskell report a module where one doesn't specify the name should implicitly be called Main. And a Main module have a function main of type IO t for some t. So Hugs should be able to figure out that the monad should be IO in this case, at least according the Haskell report. Cheers, /Josef

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crash at infinite recursion
by Felix Hummel 14 Oct '03

14 Oct '03

Hugs98 Version: Nov 2002 crashes when evaluating the following line let x = x+1 in x Of course this line is quite stupid, but none the less the interpreter should not crash... Cheers, Felix "Bumblebee" Hummel

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IO problems
by Iavor Diatchki 13 Oct '03

13 Oct '03

hello, while looking at the program henk posted a few days ago, i run into a rather weird bug in hugs, where it seems to be mixing IO handles. the problem seems to happen with versions of hugs as early as Nov 2002. it occurs on linux (Mandrake 9.1 and Redhat 9.0). this is how one can reproduce the problem: 1. place the three attahced files in a directory 2. runhugs ReadALot.hs hugs is supposed to read files names from a file (dir.dat) and then read each of these files. at some point it gets confused between the contents of "dir.dat" and the file it just read. another way to get the problem is like this: 1. hugs ReadALot.hs 2. Main> main the same thing happens. however if "main" is evaluated again, the problem does not seem to occur. yet another variation on the probelm occurs, if one of the lines in "dir.dat" is deleted (at the moment it has 41 line, but try it with 40). then "strace" reveals that hugs seems to be trying to read from stdin. bye iavor -- ================================================== | Iavor S. Diatchki, Ph.D. student | | Department of Computer Science and Engineering | | School of OGI at OHSU | | http://www.cse.ogi.edu/~diatchki | ================================================== main = print . map length =<< mapM readFile . lines =<< readFile "dir.dat" bad test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test test

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Problem with winhugs in Windows XP
by Gilberto Camara 12 Oct '03

12 Oct '03

Dear winbugs: I have recently installed Haskell on a windows XP machine. The Hugs DOS interface works fine, but I am having trouble getting "winhugs" to run. I am getting a message: "Unable to open file C:\apps\Hugs\lib\Prelude.hs" I have already performed the procedure recommended in http://haskell.org/pipermail/hugs-bugs/2002-March/000658.html which is to edit the windows registry. Unfortunately, it is still not working. Can someone point an alternative way of soliving this problem? Best regards, Gilberto ===================================== Dr.Gilberto Camara Director for Earth Observation National Institute for Space Research, Brazil (INPE) Av. dos Astronautas,1.758 - Jd. Granja - 12227-010 São José dos Campos - SP - Brasil voice: +55-12-3945-6499 fax: +55-12-3945-6460 home: www.dpi.inpe.br/gilberto =====================================

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Reading multiple files fails
by Henk-Jan.van.Tuyl 10 Oct '03

10 Oct '03

L.S., After reading through 60 or 61 files (about 220 kB), Hugs fails with the message: (1426170 reductions, 2976893 cells, 68 garbage collections) ERROR - Garbage collection fails to reclaim sufficient space This is done with the program below (ReadALot.lhs), which reads a series of files (these files are listed in dir.dat). The program reads the first and the last (non-empty) line of each file and writes them, together with the filename in the output file result.dat. The program works fine when compiled with GHC, it then reads 2946 files without a problem. More info.: System: Windows 98 Hugs version: Nov 2002 Best regards, Henk-Jan van Tuyl ====================================================================== ReadALot.lhs Read a lot of files 2003-10-06 History: 031009 Added dummy parameter to "main" ====================================================================== import IO import Monad inputSet :: String inputSet = "dir.dat" outputFile :: String outputFile = "result.dat" ====================================================================== main ====================================================================== main :: a -> IO () main _ = do hInputSet <- openFile inputSet ReadMode hOutputFile <- openFile outputFile WriteMode fileNames <- hGetContents hInputSet allData <- collectAllData $ lines fileNames hPutStrLn hOutputFile $ unlines allData hClose hInputSet hClose hOutputFile ====================================================================== collectAllData Read a list of file names and return file name, first line and last line of each file in a list ====================================================================== collectAllData :: [String] -> -- A list of filenames IO [String] -- A list of results collectAllData [] = return [] collectAllData (fileName : fileNames) = do putStrLn $ "Reading: " ++ fileName h <- openFile fileName ReadMode contents <- hGetContents h dataFromFile <- return $! parseFile $ filter (/= "") $ lines contents let (firstLine, lastLine) = dataFromFile To force reading of the file before closing, we add a "when" (from the Monad library), with a boolean expression that uses lastLine and will always be true: when (length lastLine >= 0) $ hClose h rest <- collectAllData fileNames return $ fileName : firstLine : lastLine : "" : rest ====================================================================== parseFile Returns the first and the last string of a list of strings, as a tuple ====================================================================== parseFile :: [String] -> (String, String) parseFile [] = ("", "") parseFile [x] = (x, "") parseFile (x : xs) = (x, last xs) --

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