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GHC doesn't compile Happy example
by carlos.scheidegger＠via-rs.net 01 Oct '01

01 Oct '01

Hello all. I'm trying to use GHC to compile the example parser in Happy, but with no success. I'm using GHC 5.02 for W2K, and I'm not quite sure what to do to make it work. I successfully compiled some small test cases, to see if I had installation problems, and they compiled just fine. First, the Happy example uses some functions that exist in Hugs but not in GHC, like isAlpha, isDigit and isSpace (I think so, at least, because i type ':t isAlpha' in GHCi and get 'variable not in scope'), so I created a module called CharClasses with these functions. So, I ran happy and generated calc.hs without any problems. When I try to compile calc.hs, by doing ghc -o calc.exe calc.hs CharClasses.hs I get: c:/ghc/ghc- 5.02/libHSstd.a(PrelMain__1.o)(.text+0x16)://c/tmp/ghc1756.hc: undefined reference to `__stginit_Main' c:/ghc/ghc- 5.02/libHSstd.a(PrelMain__2.o)(.text+0x4)://c/tmp/ghc1756.hc: undefined reference to `Main_main_closure' c:/ghc/ghc- 5.02/libHSstd.a(PrelMain__2.o)(.text+0x33)://c/tmp/ghc1756.hc: undefined reference to `Main_main_closure' I tried to compile each .o file separately, but I got the exact same errors. I don't know much about the structure of ghc and the interactions with gcc, but this does look like a linker error, and I'm guessing it's trying to tell me that I don't have a main function. But I do have one, as I checked the calc.hs and the main = getContents >> print . calc . lexer is there. GHCi seems to load the module just fine, and the parser and lexer seem to be working correctly. One strange thing that happens is that if I run an example from the interactive mode, it works, but if I call the main function, I get *** Exception: calc.hs:285: Non-exhaustive patterns in function lexer Another strange behavior is that I can only call the main function once. Any other call I get: Happy> main *** Exception: illegal operation Action: hGetContents Handle: {loc=<stdin>,type=semi-closed,binary=False,buffering=line} Reason: handle is closed File: <stdin> If I reload all modules with ':s' I can run it again, but also only once. I really don't know what I'm doing wrong. Can anyone help me? Thank you in advance, Carlos

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RE: GHC 5.02 is released
by Julian Seward (Intl Vendor) 01 Oct '01

01 Oct '01

Yes. There is now a ... -src-2.tar.bz2 file there; unfortunately I forgot to remove the message when I put it there. Download and compile away. J | -----Original Message----- | From: Frank Seaton Taylor [mailto:fstaylo@alpha.ncsc.mil] | Sent: Friday, September 28, 2001 8:36 PM | To: haskell(a)haskell.org | Subject: Re: GHC 5.02 is released | | | Has the problem with | | http://haskell.cs.yale.edu/ghc/dist/5.02/ghc-5.02-src-1.tar.bz2 | | described as | | Note: as posted on Friday 21 Sept, has a known minor | build-system bug. | It will | build a perfectly correct in-place compiler, but is not | quite suitable | for | building binaries for widespread distribution (package | builders please | note). | We will endeavour to post here a fixed version of the source on | Monday, once | we've had a chance to test the fix." | | been fixed yet? | | Just wondering before I download it... | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell |

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Unicode support
by Colin Paul Adams 01 Oct '01

01 Oct '01

I have just been reading through the Haskell report to refresh my memory of the language. I was surprised to see this: The character type Char is an enumeration and consists of 16 bit values, conforming to the Unicode standard [10]. Unicode uses 24-bit values to identify characters. -- Colin Paul Adams Preston Lancashire

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Re: Haskell <-> Java and floats
by Ashley Yakeley 30 Sep '01

30 Sep '01

At 2001-09-30 00:37, pachinko(a)magicaldesk.com wrote: >Has anyone ever tried to pass/receive a float to/from a Java app? If so, >how did you manage it? Using JNI through Haskell's FFI. Both define their floats and doubles as C 'float' and 'double', so I don't bother with any conversion. I haven't tested it yet, though. -- Ashley Yakeley, Seattle WA

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Layout rule
by Ian Lynagh 30 Sep '01

30 Sep '01

Hi all The report says "The layout rule matches only those open braces that it has inserted" in the lexical structure section. However, in the syntax section function L starts L (t:ts) (m:ms) = } : (L (t:ts) ms) if parse-error(t) (Note 1) which AFAICT will implicitly close an explicit open brace. Testing with "foo = let { x = 5 in x" shows hugs, ghc and nhc98 all seem to agree with me. L (t:ts) (m:ms) = } : (L (t:ts) ms) if m /= 0 && parse-error(t) (Note 1) Along similar lines, I think writing the last two lines as L [] [0] = [] L [] (m:ms) = } : L [] ms if m /=0 (Note 5) would be clearer. In fact as the preeceding text says 'and "" for the empty stream' I think it may be written correctly but have gotten lost in the conversion from whatever it is really written in. Thanks Ian

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Re: Unicode support
by Marcin 'Qrczak' Kowalczyk 30 Sep '01

30 Sep '01

30 Sep 2001 14:43:21 +0100, Colin Paul Adams <colin(a)colina.demon.co.uk> pisze: > I think it should either be amended to mention the BMP subset of > Unicode, or, better, change the reference from 16-bit to 24-bit. 24-bit is not accurate. The range from 0 to 0x10FFFF has 20.087462841250343 bits. There is no simple answer to the question "how many bits is Unicode". It's hard to decide what should go into the standard when the support for Unicode in actual implementations is still limited. For example the standard doesn't say how characters are stored in files and the current status of what implementations do is not satisfactionary (they can't store characters above '\xFF'). Unfortunately there is no simple answer here too. -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Haskell <-> Java and floats
by pachinko＠magicaldesk.com 30 Sep '01

30 Sep '01

Has anyone ever tried to pass/receive a float to/from a Java app? If so, how did you manage it? I need an algorithm for converting an IEEE 754 format float to a 32 bit integer? I want something that can convert a haskell float into a int that can be stored to disk for later input to a Java app that converts it back to a float with the Java floatToIntBits function. I think I'm OK in the reverse direction, converting an int into a float (as implemented by the Java intBitsToFloat function). The following link to the Java docs gives the bit masks and expression required to convert an int to a float. http://java.sun.com/products/jdk/1.2/docs/api/java/lang/Float.html Unfortunately, although the page gives a brief description of the the floatToIntBits function, specfically how to place the components of the floating point number into a 32 bit int, it doesn't describe how to extract those components. Things seem to be complicated a bit by things such as the hidden bit, and Java interpreting the floating point to the far left of the mantissa, instead of the far right. I found the following page describing how the floatToIntBits function works, but I think it's wrong, since when I try to run this function it gives a different integer that when I use the standard Java floatToIntBits function. Maybe the page describes a different version of the IEEE format? http://www.jos.org/redist/kore-0.0.7/java.lang.Float.src.html I'm not an expert on any of this - so any algorithm, in any language (including english), would be much appreciated. BTW - all of the above applies double (64 bit integer, doubleToIntBits/intBitsToDouble). _____________________________________________________________ Global Virtual Desktop http://www.magicaldesk.com

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Re: Wish list: expanded defaulting, dependent types, reflection
by Ashley Yakeley 30 Sep '01

30 Sep '01

At 2001-09-29 17:07, Mike Gunter wrote: >class Add a b c | a b -> c where add :: a -> b -> c >instance Add Integer Integer Integer where add = (+) >pt1 = (3::Integer) `add` (4::Integer) -- Works fine, >--ft2 = (5::Integer) `add` 6 -- Fails OK, you're running across a fundamental design shortcoming in GHC's instance overlap calculation. What you want to do is this: class Add a b c | a b -> c where add :: a -> b -> c instance (Integral a,Integral b) => Add a b Integer where add a b = (toInteger a) + (toInteger b) pt1 = (3::Integer) `add` (4::Integer) ft2 = (5::Integer) `add` 6 So far so good. The trouble comes when you want to add your own type: instance (Integral b) => Add MyInt b MyInt where add (MkMyInt a) b = MkMyInt (a + (toInteger b)) Provided you don't declare 'instance Integral MyInt', the two instances will not de facto overlap. But GHC will complain that they do, because GHC's understanding of overlapping instances is excessively conservative. This is currently top of my list of GHC problems. GHC annoyingly ignores the class contexts and simply sees this: Add a b _ Add MyInt b _ ...from which it deduces that the instances overlap. So can't you just switch on -fallow-overlapping-instances and not worry about it? Ordinarily, yes, but for some reason that doesn't work when you have a dependent parameter in your class. It's like it's a different piece of code doing the checking, or something. I've entered a bug for this, see <http://sourceforge.net/tracker/?func=detail&aid=441389&group_id=8032&atid= 108032>. I don't know if this has been fixed in 5.02. -- Ashley Yakeley, Seattle WA

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Re: Wish list: expanded defaulting, dependent types, reflection
by Mike Gunter 30 Sep '01

30 Sep '01

> >There does not seem to be a way to do everything I'd like in GHC even > >in its most permissive mode (I'm using "-fallow-overlapping-instances > >-fallow-undecidable-instances".) In particular, I'd like to use bare > >integer literals together with values of the types I define. > > Do you have a code example of what you're trying to do? Here's a simple example of the problem: class Add a b c | a b -> c where add :: a -> b -> c instance Add Integer Integer Integer where add = (+) pt1 = (3::Integer) `add` (4::Integer) -- Works fine, --ft2 = (5::Integer) `add` 6 -- Fails mike If you uncomment ft2, GHC (as expected) says: /home/gunter/haskell/hdl/PlusTest.hs:20: No instance for `Add Integer b c' arising from use of `add' at /home/gunter/haskell/hdl/PlusTest.hs:20 in the definition of function `ft2': (5 :: Integer) `add` 6 /home/gunter/haskell/hdl/PlusTest.hs:20: Ambiguous type variable(s) `b' in the constraint `Num b' arising from the literal `6' at /home/gunter/haskell/hdl/PlusTest.hs:20 In the second argument of `add', namely `6'

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Re: Wish list: expanded defaulting, dependent types, reflection
by Ashley Yakeley 29 Sep '01

29 Sep '01

At 2001-09-29 09:11, Mike Gunter wrote: >There does not seem to be a way to do everything I'd like in GHC even >in its most permissive mode (I'm using "-fallow-overlapping-instances >-fallow-undecidable-instances".) In particular, I'd like to use bare >integer literals together with values of the types I define. Do you have a code example of what you're trying to do? -- Ashley Yakeley, Seattle WA

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