List comprehensions
Hello, Recently, I came accross this expression: [ x + y | x - xs | y - ys ] As far as I can see (Haskell Report), this is not allowed by the haskell 98 standard. So I assume it to be an ex- tension. Where can I find information about this? Thanks, Rijk ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: List comprehensions
* Rijk J. C. van Haaften [EMAIL PROTECTED] [2003-01-30 11:41 +0100]: Recently, I came accross this expression: [ x + y | x - xs | y - ys ] ^ Put a comma ',' here. That's something totally different. Two examples: 1. Comma [ x + y | x - [1,2], y - [3,4] ] = [4,5,5,6] 2. Bar [ x + y | x - [1,2] | y - [3,4] ] = [ x + y | (x,y) - zip [1,2] [3,4] ] = zipWith (+) [1,2] [3,4] = [4,6] The first is according to the standard. No problems so far. However, I couldn't find a description of the semantics of the second (and it is clearly non-standard), though I think the semantics given above using zip and zipWith are correct. Rijk ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: 3 `\x y - x + y` 4 `\x y - x + y` 5: Wrong version pasted
I pasted the wrong version into the mail. This is the final one: module InfixFunction where infixl 0 $- infixr 0 $+ -- for left-associative functions ($) :: a - (a - b) - b ($) x f = f x -- for right-associative functions ($) :: a - (a - b) - b ($) x f = f x example1 :: Int example1 = -- 3`\x y - x + y` 4 3 $ (\y x - x + y) 4 example2 :: Int example2 = -- 1`\x y - x + y` 2`\x y - x` 3 1 $ (\y x - x + y) 2 $ (\y x - x + y) 3 Rijk-Jan van Haaften ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Binary search tree
Hi everybody, I studied haskell this semester at the university and I was required to implement a binary search tree in haskell. I would appreciate if anyone could send me an example code of this data structure. Just read a standard textbook. Some useful course notes by Jeroen Fokker are available online at http://www.cs.uu.nl/people/jeroen/courses/fp-eng.pdf Enough to solve your problem. Rijk-Jan van Haaften ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: ANNOUNCE: Object I/O released
The quick reference still gives problems. I managed to download the quick reference. Get it at http://www.students.cs.uu.nl/people/rjchaaft/ObjectIO/objectio-ref.zip This is a very temporarily available service, so if anyone has a suitable server (again, cvs.haskell.org?), please take over hosting the file. Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: ANNOUNCE: Object I/O released
Hello all, Peter Achten and Arjan van IJzendoorn wrote: I ... unfortunately could not open the .zip files and Peter asked Could you check the formats of these files? After having tried to download the file a few times, I believe the problem is not in the zip file format, but download failure. (Until now, I didn't manage to download more than 3 MB, though the file should be 4 MB.) Krasimir, can you please put the file on another server (maybe the cvs.haskell.org maintainers are willing to store the file; ask Jeff Lewis, [EMAIL PROTECTED])? Regards, Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Typo: Hugs Bug ! it was +
Ahn Ki-yung wrote:
Prelude f 1 where f x = x : f x
[1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
,1,1,{Interrupted!}
Prelude f 1 where f x = x + f x
-- Immediate (!) crash
Indeed, I could reproduce this on my computer
(Win2000; Hugs Dec 2001 of last week).
Rijk-Jan van Haaften
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Re: Hugs Bug !
but in windows 2000 Then suddnly interpreter fails and the red (X) popup window pops up. hugs.exe - application programm error unknown software exception (0xc000fd) ... blabla Are you sure you have the very very very latest download? There have been some undocumented updates of the December 2001 release of Hugs. Download the very latest release and try it again. I tried you expression on Win2000, with Hugs Dec 2001, downloaded last week, and it runs in constant space for an unlimited time. Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Rectification Hugs bug
Dear all, After intensive investication of several people here at Utrecht University, these are the results 1. The very latest Hugs version doesn't have the bug 2. All before-december-2001 versions don't have the bug I were using a version downloaded some weeks ago. After installing the current distribution, the problems disappeared Therefore, I suspect there have been one or more bug-fix updates after December 2001, fixing this problem. However, I couldn't find that documented on the Hugs site. Can anyone confirm such an update? Where can I find last- minute distribution information? Thanks, Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Rectification Hugs bug
Dear all, After intensive investication of several people at Utrecht University, these are the results: 1. The very latest Hugs version doesn't have the bug 2. All before-december-2001 versions don't have the bug I were using a version downloaded some weeks ago. After installing the current distribution, the problems disappeared. Therefore, I suspect there have been one or more bug-fix updates after December 2001, fixing this problem. However, I couldn't find that documented on the Hugs site. Can anyone confirm such an update? Where can I find last-minute distribution information? Thanks, Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Bug in Hugs Dec 2001: type inferencer incorrect!
Hello everybody, Although I didn't manage to reproduce the bug with a minimal example, I think it is still important enough to tell you (and especially the Hugs writers and maintainers). Yesterday evening, I tried to add some correct (!) code (by-hand-verifyable; by GHC accepted; just using plain Haskell 98) to one of the projects I'm working on. Hugs however said this: Type checking ERROR TypeInferDecls.hs:102 - Type error in application *** Expression : checkedUnify (snd newTyEnv) inferredHpPtr explicitHpPtr (\t1 t2 ue - ([l],ExplicitError n t1 t2 ue)) *** Term : checkedUnify *** Type : NonGenerics - HpPtr - HpPtr - ErrorFunction - TI Error () *** Does not match : a - b - c - d - e *** Because: types do not match I've read this ten times, checked my code looking whether I were doing strange things, but I can only conclude: This is, even without a minimal example, clearly a bug: the types do match. Moreover, the bug is reported about a completely different part of the file (relative to the location I edited), in code almost unrelated to the code I added (about line 300). I have explicit types everywhere in that file, so if it were wrong, the error should be reported about line 300. So the reporting-place is wrong (but I don't expect Hugs to report good error-placement). Though I didn't manage to write a minimal example, I hope our Hugs experts are able to find the bug soon. As a last point: the file is rather big: 726 lines of code, 27KB. Rijk-Jan van Haaften ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Bug in Hugs Dec 2001: type inferencer incorrect!
Hello everybody, Although I didn't manage to reproduce the bug with a minimal example, I think it is still important enough to tell you (and especially the Hugs writers and maintainers). Yesterday evening, I tried to add some correct (!) code (by-hand-verifyable; by GHC accepted; just using plain Haskell 98) to one of the projects I'm working on. Hugs however said this: Type checking ERROR TypeInferDecls.hs:102 - Type error in application *** Expression : checkedUnify (snd newTyEnv) inferredHpPtr explicitHpPtr (\t1 t2 ue - ([l],ExplicitError n t1 t2 ue)) *** Term : checkedUnify *** Type : NonGenerics - HpPtr - HpPtr - ErrorFunction - TI Error () *** Does not match : a - b - c - d - e *** Because: types do not match I've read this ten times, checked my code looking whether I were doing strange things, but I can only conclude: This is, even without a minimal example, clearly a bug: the types do match. Moreover, the bug is reported about a completely different part of the file (relative to the location I edited), in code almost unrelated to the code I added (about line 300). I have explicit types everywhere in that file, so if it were wrong, the error should be reported about line 300. So the reporting-place is wrong (but I don't expect Hugs to report good error-placement). Though I didn't manage to write a minimal example, I hope our Hugs experts are able to find the bug soon. As a last point: the file is rather big: 726 lines of code, 27KB. Rijk-Jan van Haaften ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Why is this function type-correct
Hello, Recently, I wrote a function similar to x :: a x = x 42 which is type-correct (Hugs, Ghc, THIH). Still, from the expression it is clear that the type shoud have a function type. The definition x :: a - b x = x 42 is equally well accepted, though I can't see why this type would be correct. (I'd expect it to be too general.) ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Why is this function type-correct
Hello, Recently, I wrote a function similar to x :: a x = x 42 which is type-correct (Hugs, Ghc, THIH). Still, from the expression it is clear that the type shoud have a function type. The definition x :: a - b x = x 42 is equally well accepted, though I can't see why this type would be correct. (I'd expect it to be too general.) For what reasons are these types considered correct? Thanks, Rijk-Jan ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Ground Up
Jerry wrote However, my problems are: * I still don't understand most of the codes I found, like the various haskell libraries Practice is the only answer to this problem, as Keith Wansbrough says. * I still have no clue of most (ok, almost all) of what is being discussed in this mailing list Though I am a CS student, being highly interested in Haskell and practising a lot, I didn't understand most of the discussions on this mailing list. I started understanding them only after I got involved in implementing a Haskell compiler. Therefore, don't worry about this point. A haskell-user doesn't need to know the details of the haskell compiler ins and outs. Rijk-Jan van Haaften ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Help
You probably want to do something like this:
main =
do {
contents - input twoboxes.dat
return (control (parser contents))
}
At 11:53 25-02-02 -0300, Juan M. Duran wrote:
Hi, I'm writting a small parser in Haskell and, when it is all done, I get
the following problem: Type Binding.
The thing is, I have 3 main functions:
1) Read the file, its type is: [Char] -IO [Char] (see InputOutput.hs)
2) Parse a string (using words and readDec), its type is: Integral a =
[Char] - [a] (see Parse.hs)
3) Parse a list of integer, its type is: [Float] - [[Float]]
(Functions.hs)
Now the problem is that I cannot run the first function, then use its
results as an input of the second function and, finally, its results as
the input of the third function.
How can I fix this without modifing all my functions because they,
independly, works fine.
Juan
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ANNOUNCE: Haskell support for JCreator update
Dear reader, I'm pleased to announce the availability of a release of the Haskell module for JCreator. You can get it, as usual, at http://www.students.cs.uu.nl/people/rjchaaft/JCreator The previous update lacks the documentation tool, and is quite restrictive concerning the location of Hugs, the Haskell Graphics Library and JCreator. This update reintroduces the documentation tool. The problems that were reported about the tool (incompatibilities between windows versions) are fixed (hopefully). The html version of Bernie Pope's Tour of the Haskell Prelude, made by Arjan van IJzendoorn is included as well (under the same documentation tool). The requirement that Hugs, the GraphicsLib and JCreator are installed in certain directories is removed, thanks to the use of a new installer. Enjoy, Rijk-Jan van Haaften ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Specifying Kinds of Types
Ashley Yakeley wrote: I'd like to be able to declare the kinds of new types and synonyms, because sometimes Haskell can't infer them. For instance: data CMap0 p q = MkCMap0; Without evidence, Haskell assumes that p and q have kind '*' (as per sec. 4.6), and therefore CMap0 has kind '* - * - *'. Actually, I wanted p and q to both have kind '* - *', giving CMap0 kind '(* - *) - (* - *) - *'. ... It's not currently possible to specify kinds, is it? It is possible using a trick due to John Hughes. In Proceedings of the 1999 Haskell Workshop, he wrote in his article Restricted Data Types in Haskell this note: 3 There is one unpleasant hack in the figure: The constructor Unused in the data type definition for Set. It is there purely in order to force the compiler to assign the parameter cxt the correct kind: without it, cxt does not appear at all in the right hand side of the definition, and is therefore assigned the (incorrect) kind *. The application cxt a forces the correct kind * - * to be assigned, and embedding it in the type cxt a - () prevents the type of the context from interfering with the derivation of a Show instance. The figure mentioned contains data Set cxt a = Set [a] | Unused (cxt a - ()) deriving Show You can follow the example of John, writing data CMap0 p q = MkCMap0 | Unused (p a - ()) (q a - ()); (I think I'm correctly applying the trick, but other Proceedings-readers will correct me if I'm wrong.) As John writes, this is a hack, but we have no other choice. Rijk-Jan van Haaften ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Problem with 'nested' pattern matching
carlos wrote: Hello. I'm having some trouble trying to understand exactly what's behind the rule for pattern-matching with data constructors. The code I'm having trouble with is similar to this: f (C p1 p2 (C2 p3 p4)) = ... f _ = False What happens is if f is called with (C p1 p2 (NOT_C2 ...)), I get a program error, and not False. I tried this in Hugs: data Test = C Bool Bool Test | C2 Bool Bool | NOT_C2 Int f :: Test - Bool f (C p1 p2 (C2 p3 p4)) = (p1 p3) || (p2 p4) f _ = False evaluating f (C True False (NOT_C2 25)) gives False as expected. Which compiler/interpreter do you use? Which version? Actually I can't imagine a bug of this kind in any of the mainstream compilers (GHC, HBC, NHC and NHC) and interpreters (Hugs, GHCi, and HBI), though on this computer I only can check hugs. Regards, Rijk-Jan van Haaften
RE: n+k patterns
At 03:27 30-01-02 -0800, Simon Peyton-Jones wrote: | hbc is on the Integral side, if that counts. :-) | Just because ghc doesn't follow the spec isn't a good reason | to change the spec. :-) I absolutely didn't say that! All I'm saying is * Two of the four impls have to change regardless * The change is non-de-stabilising on the rest of the report * So we should think what the best answer is I argued that (Num a, Ord a) makes most sense to me. You argued that (Integral a) was a conscious choice (something I don't remember but I'm sure you're right), and is the right one anyway. I'd be interested to know what others think. If there's any doubt, we'll stay with Integral. Personally I vote for keeping Integral. The strongest reason for my choice is that if we want to be sure the pattern is really correct, we need a bijection. For Integral, we have + and - to form one, but we can't construct one for Float and Double, though by this change they would be allowed in the pattern. Rijk-Jan van Haaften ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
