October 2000 - Hugs-Bugs

OSX
by Michel Schellekens 25 Oct '02

25 Oct '02

After downloading the OSX version, and typing "hugs" to start up the language, I obtain the following error: [schellekens:~] mpcs% hugs dyld: hugs can't open library: /usr/lib/libncurses.5.dylib (No such file or directory, errno = 2) Any suggestions? Michel.

2 1

Abstract data types
by Ángel Herranz-Nieva 31 Oct '00

31 Oct '00

Hello, we give a course on data structures at School of Computer Science (Technical University of Madrid) and we use Hugs as the Haskell interpreter in such a course. Our problem has to do with hiding concrete types representing abstract types. I have attached our module for the abstract data type Stack (we follow the Haskell 98 report and don't want to go into 1.4 compatibility). We expected the representation of stacks were hidden but Hugs let us write an expression with the "hidden" constructor StackC: Stack> :l Stacks Reading file "Stacks.hs": Parsing.................... Dependency analysis........ Type checking.............. Compiling.................. Hugs session for: /opt/lib/hugs/lib/Prelude.hs Stacks.hs Stacks> StackC [1] StackC [1] Stacks> This problem occurs only in the top level, if we program a client module importing the module Stacks and we try to write a expression using directly StackC then Hughs gives an error message (great!). This is a bug in the top level, isn't it? Thank you very much in advance. -- Angel Herranz-Nieva (FI-UPM) pho: +34 913367452 mailto:aherranz@fi.upm.es http://lml.ls.fi.upm.es/~angel -- Stacks.hs: an abstract data type for stacks module Stacks (Stack, emptyStack, push, pop, topOf, isEmpty) where newtype Stack a = StackC [a] deriving Show emptyStack :: Stack a push :: a -> Stack a -> Stack a pop :: Stack a -> Stack a topOf :: Stack a -> a isEmpty :: Stack a -> Bool emptyStack = StackC [] push x (StackC p) = StackC (x:p) pop (StackC []) = error "pop: empty stack" pop (StackC (_:xs)) = StackC xs topOf (StackC []) = error "topOf: empty stack" topOf (StackC (x:_)) = x isEmpty (StackC p) = null p

2 2

(no subject)
by D.Wakeling＠exeter.ac.uk 28 Oct '00

28 Oct '00

To: hugs-bugs(a)haskell.org Subject: bug in Classic Hugs Feb 2000 Hello, I believe there is a bug in Classic Hugs version Feb 2000. On my Red Hat 6.2 PC, the manual page for fgetpos(3) says: RETURN VALUES The rewind function returns no value. Upon successful completion, fgetpos, fseek, fsetpos return 0, and ftell returns the current offset. Yet in the function primFun(primHGetPosn) in the file hugs98/src/iomonad.c there are the lines: primFun(primHGetPosn) { /* Get file position */ Int h; HandleArg(h,3); if (handles[h].hmode!=HCLOSED) { #if HAVE_FGETPOS fpos_t pos; if (fgetpos(handles[h].hfp,&pos)) { /* <---- WRONG! --- */ IOReturn(mkInt((Int)pos)); } #elif HAVE_FTELL /* A reasonable approximation for pre-ANSI compilers */ long pos = ftell(handles[h].hfp); IOReturn(mkInt((Int)pos)); #else /* deliberate fall through to IOFail */ #endif The line indicated as "WRONG" above should be if (fgetpos(handles[h].hfp,&pos) == 0) { The use of fsetpos(3) looks similarly wrong. David ------------------------------------------------------------------------------- Dr. David Wakeling, School of Engineering and Computer Science University of Exeter, Exeter, Devon, EX4 4PT. unofficial web page: http://www.dcs.ex.ac.uk/~david -------------------------------------------------------------------------------

2 1

win 95?
by EW 27 Oct '00

27 Oct '00

is there no version of hugs working with win 95? EW __________________________________________________ Do You Yahoo!? Yahoo! Messenger - Talk while you surf! It's FREE. http://im.yahoo.com/

2 1

(no subject)
by Paula Severi 25 Oct '00

25 Oct '00

Hi, The type inferred by the functions zero = 0 and zero2 = 0.0 are Main> :t zero zero :: Integer Main> :t zero2 zero2 :: Double Is this an error? I think it should give the type Num a => a, or not? At least it is more practical. Best regards, Paula ********************************************************************* Centro de Matematica, Facultad de Ciencias Igua 4225 esq. Mataojo, CP 11400. Montevideo, Uruguay severi(a)cmat.edu.uy Tel. 598 2 5252183 (int. 128) Fax 598 2 5220653 *********************************************************************

2 1

Re: bug?
by Friedrich Dominicus 25 Oct '00

25 Oct '00

Paul Hudak <paul.hudak(a)yale.edu> writes: > > You must have an old version of Haskore. The one currently at > haskell.org/haskore (which has been stable for awhile) does not have > this problem. Someone pointed that out and I downloaded the newest version, of course things worked Regards Friedrich -- for e-mail reply remove all after .com

1 0

type inference and type checking are different
by Paula Severi 24 Oct '00

24 Oct '00

For the example of the previous message, the type inference of zero = 0 yields Integer. Though if we write zero:: Num a => a zero = 0 the type together with the function it is succesfully type checked. The type inference does not yield the most general type though the type checking is doing it properly. Paula ********************************************************************* Centro de Matematica, Facultad de Ciencias Igua 4225 esq. Mataojo, CP 11400. Montevideo, Uruguay severi(a)cmat.edu.uy Tel. 598 2 5252183 (int. 128) Fax 598 2 5220653 *********************************************************************

1 0

bug?
by Friedrich.Dominicus＠t-online.de 24 Oct '00

24 Oct '00

Dear ladies and gentlemen, I'm trying to learn Haskell using Hugs. On my experiments I tried to run the Haskore example. But I get the following error: ERROR "/usr/local/share/hugs/lib/hugs/../Haskore/src/Monads.hs" (line 55): No member "map" in class "Functor" Now I looked into the Prelude and there one can just find fmap class Functor f where fmap :: (a -> b) -> (f a -> f b) Now there is obvious no map. So I guess it must either be added or the Monads.hs from Haskore have to be patched. Regards Friedrich

4 3

weired bug
by Tim Gahnstr�m /Bladerman 21 Oct '00

21 Oct '00

Hi I dont know if this bug is of much interest to you since it aply to Version: September 1999. If you are uninterested, just disregard from this mail. On most hugs interpretators (which I have tries it on) the call add 1 [0,0,1] will return [1,0,1] But on my instalation (both winhugs and the dos mode) return [0,1,1] I dont have a clue why but here is the actual code. The correct return is [1,0,1] halvad (0,0) = (0,0) halvad (1,0) = (0,1) halvad (0,1) = (0,1) halvad (1,1) = (1,0) add 0 [] = [] add 1 [] = [1] add carry (x:xs) = let (car,out) = halvad (carry,x) in (out:(add car xs)) Good luck and happy buggtraquing. TIm Gahnström

1 0

Module system bug
by Koen Claessen 18 Oct '00

18 Oct '00

Hi, (I know that Hugs does not claim to implement the whole module system, but I consider the following a bug anyway.) Consider the following 4 modules: module Top where import C main = print "koe" module C( module A, module B ) where import A hiding ( apa ) import B hiding ( apa ) module A where apa = "one" module B where apa = "two" Hugs does not complain when loading C (and indeed it shouldn't), but complains about importing C (conflict with the function "apa") when loading Top. This is the February 2000 version of Hugs running on SunOS. /Koen. -- Koen Claessen http://www.cs.chalmers.se/~koen phone:+46-31-772 5424 mailto:koen@cs.chalmers.se ----------------------------------------------------- Chalmers University of Technology, Gothenburg, Sweden

2 1