May 2003 - Haskell-Cafe

re: re: 你好
by 张丽 14 May '03

14 May '03

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Re: on termination
by Markus.Schnell＠infineon.com 14 May '03

14 May '03

Somebody asked for coffee? / / / \ \ \ / / / +++++++++++ + +--\ + +___/ \+++++/ ============= ========= -- Markus Schnell Infineon Technologies AG, CPR ET Tel +49 (89) 234-20875

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DUKAT KABILA(Jnr)
by Dukat Kabila 13 May '03

13 May '03

> MR DUKAT KABILA 0031+615-421-228 > REQUEST FOR URGENT BUSINESS ASSISTANCE > >Your contact was availed to me by the chamber of commerce. It was given to me because of my diplomatic status as I did not disclose the actual reasons for which I sought your contact. But I was assured That you are reputable and trustworthy if you will be of assistance. I am Laurent DUKAT KABILA (Jnr) the second son of Late President LAURENT DESIRE KABILA the immediate Past president of the DEMOCRATIC REPUBLIC OF CONGO in Africa who was murdered by his opposition through his personal bodyguards in his bedroom on Tuesday 16th >January, 2001.I have the privilege of being mandated by my father colleagues to seek your immediate and urgent co-operation to receive into your bank account the sum of US$25m.(twenty-five million Dollars) and some thousands carats of Diamond. This money and treasures was lodged in a vault with a security firm in Europe and South-Africa. > >SOURCES OF DIAMONDS AND FUND >In August 2000, my father as a defence minister and president has a meeting with his cabinet and armychief about the defence budget for 2000 to 2001 which was US $700m. so he directed one of his best friend. Frederic Kibasa Maliba who was a minister of mines and a political party leader known as the Union Sacree de, I opposition radicale et ses allies (USORAL) to buy arms with US $200m on 5th January 2001; for him to finalized the arms deal, >my father was murdered. f.K. Maliba (FKM) and I have decided to keep the money with a foreigner after which he will use it to contest for the political election. Inspite of all this we have >resolved to present your or your company for the firm to pay it into your nominated account the above sum and diamonds. This transaction should be finalized within seven (7) working days and for your co-operation and partnership, we have unanimously agreed that you will be entitled to 5.5% of the money when successfully receive it in your account. The nature of your >business is not relevant to the successful execution of this transaction what we require is your total co-operation and commitment to ensure 100% risk-free transaction at both ends and to protect the persons involved in this transaction, strict confidence and utmost secrecy is >required even after the successful conclusion of this transaction. If this proposal is acceptable to you, kindly provide me with your personal telephone and fax through my E-mail box for immediate commencement of the transaction. >All correspondence is for the attention of my counsel: > >I count on your honour to keep my secret, SECRET. >Looking forward for your urgent reply >Thanks . >Best Regards > >DUKAT KABILA(Jnr) >

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How to create an unboxed array?
by Ron de Bruijn 13 May '03

13 May '03

I finally succeeded in creating the unsafeWrite and unsafeRead functions, but the newArray_ function will not work. I get the following error: Compiling Try ( try.hs, interpreted ) try.hs:37: Could not deduce (Num i) from the context (MArray IOUArray Foo IO, HasBounds IOUArray, Monad IO, Ix i) Probable fix: Add (Num i) to the class or instance method `newArray_' arising from use of `*' at try.hs:37 In the first argument of `newArray_', namely `(fst (bound), (snd (bound)) * 2)' In a 'do' expression pattern binding: newArray_ (fst (bound), (snd (bound)) * 2) Failed, modules loaded: none. Prelude> newArray_ bound= do newArray_ (fst(bound),snd(bound)*2) I don't really understand why I have to do something with the Numclass. I think it is to be sure of the fact that the the arguments given in the tuple are indextypes of type Num, so the values can always be multiplied using the * operator. How can I make this work and why will it work the way you would say it would work? And why can't I just put the types of the functions just above the definition, just like I do with any other function, is it just because of the fact this is a method of a class? newArray_::(MArray a e m, Ix i) => (i, i) -> m (a i e) newArray_ bound= do newArray_ (fst(bound),snd bound)) And then yet another question: if I had another datatype, like Foo String Int, then I just had to create two different arrays, one of Int and one of String, right? Greets Ron __________________________________ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo. http://search.yahoo.com

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Web Server
by Shawn P. Garbett 13 May '03

13 May '03

I got into a discussion with folks in my local circle of computer heads. I was talking about what I liked about Haskell. Most of the local circle are sold on the idea that Perl is the best language ever written. They eventually challenged me: show us a web site that is being served by Haskell. Does anyone out there run a web site using Haskell? How much effort would be involved in creating a haskell_mod to plug into apache? Shawn

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Re: CC: Functional dependencies question
by oleg＠pobox.com 13 May '03

13 May '03

> > then the user can write > > hbar = 6.62606876e-34 `scalarm` (joule `mult` second) > That works, but IMO it's a bit unwieldy. It also doesn't help with > actually defining a reasonable type signature for hbar which is the > point of the exercise. Well, how about this? hbar = (PhysicalUnit 6.62606876e-34)::t where x::t = (undefined::Energy) `mult` (undefined::Time) the use of bottom might be a bit bizarre -- OTH, a physicist of a kind that cares about Planck constant should get used to the infinities -- take QED for example. A physicist might even appreciate that equation. It's interesting that in every thread I have participated over the last couple of months I mentioned 'undefined'. It must be my favorite Haskell value.

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CC: Functional dependencies question
by oleg＠pobox.com 12 May '03

12 May '03

Hello! Andrew J Bromage wrote: > class Foo a b | a -> b where > foo :: a -> b > > bar :: (Foo Char t) => t > bar = foo 'a' > > All well and good so far. Let's add an instance of Foo... > > instance Foo Char Bool where > foo c = isAlpha c > > Now neither GHC nor Hugs will allow this to compile, as the declared > type of bar is "too general". The type of bar is indeed too general. It should be bar:: forall t. (Foo Char t | Char -> t) => t or bar:: exists t. (Foo Char t) => t because the functional dependency implies that there can be only one such type that relates to Char. Yet such types are not expressible. Perhaps because of that, GHC and Hugs delay reporting an error. For example, if we omit the instance declaration, both GHC and Hugs seem happy. But they only seem. In Hugs, if we try to actually evaluate 'bar', we get Main> bar ERROR - Unresolved overloading *** Type : Foo Char a => a *** Expression : bar Indeed, an instance declaration is required. Incidentally, GHC can report the error even before running the code: if we just want to see the type of bar: *Main> :t bar No instance for (Foo Char t) arising from use of `bar' at <No locn> If we add an instance of Foo, such as "instance Foo Char Bool", then the signature of bar is clearly too polymorphic: there can be only one type t (namely, Bool) for which the constraint Foo Char t is true. Incidentally, local type variable again seem to help -- they can help express types that are normally inexpressible. If we define bar as bar :: (Foo Char t) => t bar ::tbar = (foo::(Char->tbar)) 'a' we get an error: /tmp/f.hs:10: Inferred type is less polymorphic than expected Quantified type variable `t' escapes It is mentioned in the environment: tbar = t is bound by the pattern type signature at /tmp/f.hs:1 When trying to generalize the type inferred for `bar' Signature type: forall t. (Foo Char t) => t Type to generalise: t When checking the type signature for `bar' When generalising the type(s) for `bar' which alerts us that the given type of bar is indeed too general. Now, we get the error right away. If we drop the explicit type declaration, bar ::tbar = (foo::(Char->tbar)) 'a' we get another error, /tmp/f.hs:12: No instance for (Foo Char tbar) arising from use of `foo' at /tmp/f.hs:12 When checking the type signature of the expression: foo :: Char -> tbar In the definition of `bar': (foo :: Char -> tbar) 'a' The compiler demands to see an instance of Foo Char t. If we add the instance now, the compiler is happy. bar ::tbar = (foo::(Char->tbar)) 'a' instance Foo Char Bool where foo c = c == 'a' *Main> bar True and the code even runs.

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Functional dependencies question
by Andrew J Bromage 12 May '03

12 May '03

G'day everyone. Suppose I have code like this: class Foo a b | a -> b where foo :: a -> b bar :: (Foo Char t) => t bar = foo 'a' All well and good so far. Let's add an instance of Foo... instance Foo Char Bool where foo c = isAlpha c Now neither GHC nor Hugs will allow this to compile, as the declared type of bar is "too general". This seems intuitively the wrong behaviour. Either the original program was incorrect (as there was no visible instance of Foo for type Char) or the amended program is correct (since the type of bar is no more general than it was in the first version). Thoughts? Cheers, Andrew Bromage

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RE: Web Server
by Markus.Schnell＠infineon.com 12 May '03

12 May '03

You could ask the guys at http://www.informatik.uni-freiburg.de/~thiemann/haskell/WASH/ Markus > -----Original Message----- > From: Shawn P. Garbett [mailto:listman@garbett.org] > Sent: Monday, May 12, 2003 3:44 PM > To: haskell-cafe(a)haskell.org > Subject: Web Server > > > I got into a discussion with folks in my local circle of > computer heads. I was > talking about what I liked about Haskell. Most of the local > circle are sold > on the idea that Perl is the best language ever written. They > eventually > challenged me: show us a web site that is being served by Haskell. > > Does anyone out there run a web site using Haskell? > How much effort would be involved in creating a haskell_mod > to plug into > apache? > > Shawn > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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haskell-cafe
by sms 11 May '03

11 May '03

你要的网页给你找到了 http://www.creatonly.com/sohusms.htm

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