Re: gcd 0 0 = 0
Lars Henrik Mathiesen ([EMAIL PROTECTED]) wrote: : > Alan Bawden ([EMAIL PROTECTED]) wrote: : > : Indeed, that's a nice way of putting it. How about if the report just : > : says: : > : : > :In order to make the non-negative integers into a lattice under `gcd' : > :and `lcm', we define `gcd 0 0 = 0'. [snip] : This is exactly what you get if you plug the relation 'divides' on the : non-negative integers into the definition of meet in a lattice. So : this formulation is no more or less complex to use than the lattice : one --- and people who do know about lattices will probably realize : this pretty fast. I disagree. Alan is talking about adding things to the haskell report. That document should be accessible to as many people as possible. I have not yet met anybody who had lattice theory in primary and/or secondary school. On the other hand I *have* met quite a few of them who have a pretty good idea about what it means for one number to divide another. [snip] Regards, Marc van Dongen -- Marc van Dongen | [EMAIL PROTECTED] | Computer Science Department | Western Road | () ASCII ribbon campaign University College Cork |Cork, Ireland | /\ against HTML mail phone: +353 (0)21 4903578 | fax: 4903113 | ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: gcd 0 0 = 0
Alan Bawden ([EMAIL PROTECTED]) wrote: :In case it isn't clear already, these definitions make a lattice on :the positive integers, with divides ~ leq, gcd ~ meet and lcm ~ join, :using the report's definitions of gcd and lcm. : : Indeed, that's a nice way of putting it. How about if the report just : says: : :In order to make the non-negative integers into a lattice under `gcd' :and `lcm', we define `gcd 0 0 = 0'. It would surely make things a lot less accessible to people (including me) who do not have any (or limited) knowledge about lattices. Why not make it more accessible and use the following rule (ore something similar)? The greates common divison (gcd) of two integers a and b is the unique non-negative integer g which has each of the following two properties: 1) g divides both a and b; and 2) if g' also divides both a and b then g' also divides g, Here an integer a divides an integer b if there is an integer c such that b = c*a. Note that if you regard an integer a to be greater than another integer b if b divides a then the gcd of two intgerers may also be regarded as the greatest common divisor of a and b. Regards, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: gcd 0 0 = 0
Ch. A. Herrmann ([EMAIL PROTECTED]) wrote: : In contrast, 0*x=0, thus 0 "divides" 0 (somehow). : But I have problems with "gcd being the greatest positive integer ..." [snip] : - 0 is not positive, it is non-negative or natural : - 2 also divides 0 and 2 is a "greater integer" than 0 : (0 is the top element of the lattice formed by the division relation :but that is not clear by the expression "greatest") : gcd a b is the greatest non-negative integer dividing both a and b such that anything that divides both a and b also divides gcd a b (so gcd a b is the greatest thing that divides both a and b). Regards, Marc van Dongen -- Marc van Dongen | [EMAIL PROTECTED] | Computer Science Department | Western Road | () ASCII ribbon campaign University College Cork |Cork, Ireland | /\ against HTML mail phone: +353 (0)21 4903578 | fax: 4903113 | ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: gcd 0 0 = 0
Marc van Dongen ([EMAIL PROTECTED]) wrote: : An integer $a$ divides integer $b$ if there exists an integer : $c$ such that $a c= b$. [snip] : gcd 0 0 = 0; and : gcd 0 0 /= error "Blah" To make clear why $0$ (and not any other non-zero integer) is the gcd of $0$ and $0$ I should have added that for the integer case $g$ is called a greatest common divisor (gcd) of $a$ and $b$ if it satifies each of the following two properties: 1) $g$ divides both $a$ and $b$; 2) if $g'$ is a common divisor of $a$ and $b$ then $g'$ divides $g$. First notice that $0$ is a gcd of $0$ and $0$ because of the following: *) $0$ divides $0$ (and divides $0$); *) whenever $g'$ is an integer that divides $0$ and divides $0$ then $g'$ divides $0$. Next notice that if $g$ is any non-zero integer then $g$ cannot be a gcd of $0$ and $0$ because $0$ (a common divisor of $0$ and $0$) does not divide $g$. Finally, observe that this makes $0$ the unique gcd of $0$ and $0$. : The gcd of two integers is usually defined as a non-negative : number to make it unique. Regards, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: gcd 0 0 = 0
Simon Peyton Jones ([EMAIL PROTECTED]) wrote: : If someone could write a sentence or two to explain why gcd 0 0 = 0, : (ideally, brief ones I can put in the report by way of explanation), : I think that might help those of us who have not followed the details : of the discussion. Division in the context of gcds (of integers) is usually defined along the lines of: An integer $a$ divides integer $b$ if there exists an integer $c$ such that $a c= b$. Note that here division is a *relation* an not a *function*/*operator*. Given the definition of division being a relation it makes perfect sense to say that $0$ divides $0$ which is why gcd 0 0 = 0; and gcd 0 0 /= error "Blah" The gcd of two integers is usually defined as a non-negative number to make it unique. HTH. PS: I am strongly in favour of gcd 0 0 = 0. Regards, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: code for exercise 4.10
rock dwan ([EMAIL PROTECTED]) wrote: : Iam having some difficulties doing exercise 4.10 from craft of fucntional : programming book ..is their a possible solution for this ? Can we please move this thread to the haskell cafe? Thanks in advance, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: computer language shootout
Miles Egan ([EMAIL PROTECTED]) wrote: [shootout] Before it starts to explode, can we move this thread to the Haskell Cafe? Regards, Marc -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 Western Road, Cork, Ireland | Email: [EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Two Times [was Re: Happy and Macros (was Re: ANNOUNCE: Happy 1.10 released)]
Manuel M. T. Chakravarty ([EMAIL PROTECTED]) wrote: [received message twice] Am I just the only one or does everybody receive messages posted to [EMAIL PROTECTED] and [EMAIL PROTECTED] twice? I find it a bit (I know I am exaggerating) annoying. Is there a way to avoid this? Regards, Marc ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Help about programming a module in haskell ?
Mickaël GAUTIER ([EMAIL PROTECTED]) wrote: : Hi, i am a french beginner in programming in haskell language. My first module :was to prove that a boolean proposition is always right. So it was about logical :mathematic. Now i am trying to program a modul which function not with mathematic :rules but with logical rules as in Prolog. I've a game named nani (it's a boy who :wants to find his nani which is in one of the three rooms of the house) wrote in :prolog and i'm trying to convert it in haskell. If someone is interest by my subject :can he send me his e-mail adress ? : Thanks Mickaël GAUTIER Hi, There is a Prolog module for Haskell but when I tried to locate it I couldn't find it. Perhaps somebody can help. Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED] ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: `Covertible' class. Reply.
S.D.Mechveliani ([EMAIL PROTECTED]) wrote: [snip] : The basic algebra library BAL : http://www.botik.ru/pub/local/Mechveliani/basAlgPropos/bal-pre-0.01/ : : suggests class Cast a b where cast :: a -> b -> a I just want to add that this is almost similar to a mechanism I've implemented. You really need this. Regards, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Re: Group theory
Eric Allen Wohlstadter ([EMAIL PROTECTED]) wrote: : Are there any Haskell libraries or programs related to group theory? I am : taking a class and it seems like Haskell would be a good programming : language for exploring/reasoning about group theory. What I had in mind : was perhaps you could have a function which takes a list(set) and a : function with two arguments(binary operator) and checks to see whether or : not it is a group. I think it might be a fun exercies to write myself but : I'd like to see if it's already been done or what you guys think about it. I think Sergey Mechveliani's docon (algebraic DOmain CONstructor) has facilities for that. Have a look at: http://www.cs.bell-labs.com/who/wadler/realworld/docon.html Regards, Marc van Dongen ___ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
Prelude in LaTeX
Hello all, Is there anybody who knows where to find the Prelude typeset in Manuel Chakravarty's haskell.sty? Thanks in advance for any replies. Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: static evaluation of dynamics thing
Simon Peyton Jones ([EMAIL PROTECTED]) wrote: [static] : said, some functions are legitimately bottom. But think about assertions: : : f x = assert (p x) (...x...) : : where assert :: Bool -> a -> a I like that. Also I would like a assertAndBelieveMe which could be used to as in: quot' a b | assertAndBelieveMe (b /= 0) = quot a b So that a special version of quot could be used which would not check for b == 0. : Life is short. Are these features that would be useful to lots of people? Yes please. Regards, Marc van Dongen
Re: sample argument. Dongen's example
S.D.Mechveliani ([EMAIL PROTECTED]) wrote: [I cc'd this to haskell as well] : this is exactly the Domain conversion proposal, described in : basAlgPropos. class Cast a b where cast :: a -> b -> a. : The first argument is the sample for domain. The second casts to : `a' after the given sample. For example cast (x^2+y (in Z[x,y)) 2 : maps 2 to polynomial in x,y : - if the instance Cast (Pol ..) Integer : is defined. I knew you must have had something to obtain a similar functionality this as well. It is needed. Regards, Marc
[dongen@cs.ucc.ie: Re: sample argument. Dongen's example]
Sorry about this. I thought I group replied when replied Sergey's e-mail. -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED] - Forwarded message from Marc van Dongen <[EMAIL PROTECTED]> - Date: Mon, 8 May 2000 11:14:03 +0100 From: Marc van Dongen <[EMAIL PROTECTED]> To: "S.D.Mechveliani" <[EMAIL PROTECTED]> Subject: Re: sample argument. Dongen's example X-Mailer: Mutt 1.0.1i In-Reply-To: <[EMAIL PROTECTED]>; from [EMAIL PROTECTED] on Mon, May 08, 2000 at 01:16:09PM +0400 S.D.Mechveliani ([EMAIL PROTECTED]) wrote: : Looks like it uses the sample argument. This p contains the : parameters that describe a polynomial domain P = c[x1..xn]. : Different ways to order the monomial set, different lists of : "variables" may mean different domains inside the *same type*. : If p contains variables ["x"], p' contains ["x","y"], : then zero p and zero p' : : have to be zeroes of very different domains corresponding to : p, p' :: a. : If you rely on the features like this, this is the very sample : argument approach. : Do you mean this? No. I meant that I didn't understand the second sentence above the one where I started my reply:-) : Classic Haskell approach: : - [] : Besides several technical hindrances of mathematical nature, it : puts certain principal restriction. : It prohibits all the mathematical practice of dynamic change of : orderings, variable lists, residue domains for different base, : generally - dynamic change of computation domain given by : *parameter*. Exactly. This has been a *great* pain in the neck for me when writing operations on polynomials using standard notation which alowed for the hiding of the additional information needed to implement fast algorithms. [...] : I suggest now zero :: a -> a or constant :: a -> c -> Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED] - End forwarded message -
Re: sample argument. Dongen's example
S.D.Mechveliani ([EMAIL PROTECTED]) wrote: : I wrote to list, and you reply privately. Ooops. I thought I group replied. I'll forward to the list. : I think that it is good for the list to know that someone else : appreciates the need of dynamic parameters in domain ... Which is why I decided to add something to the discussion. : But I an dumb at your> or constant :: a -> c -> : : For example, zero (2,3) = (0,0) gives zero for Int x Int. : And how to use `constant' ? Say you have a constant c in some ring k and you want to lift it (I think that's the proper term) to the polynomial ring k[X] then you can if you have a polynomial, say p, in k[X] already. Just use: constant p c. Regards, Marc -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: basAlgPropos. Why sample argument
Fergus Henderson ([EMAIL PROTECTED]) wrote: [snip] : > * `zero x' fits the aim of implicit dynamic domains. : : This one is much more interesting. I am not sure if I understand this but I also used zero :: a -> a to create polynopmials as opposed to a function zero :: a The application zero p created a zero polynomial with certain ``built-in'' properties like a term-order it inherited from p. Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: doubly linked list
Jerzy Karczmarczuk ([EMAIL PROTECTED]) wrote: : But in Haskell, where the beasts are not mutable: : : ... Actually, has anybody really used them for practical purposes? I have used doubly linked lists in Haskell about four years ago to implement a queue from which objects could be added at front/back and deleted anywhere. A mutable array was used to see if objects were in the queue. If they were then (Just Ix) to them would be returned and if they weren't Nothing. The index could then be used to find the possible previous and next elements in the queue and change their representations. I cheated a bit because I used the fact that the possible indices were know in advance so that I could use an array to represent the member in the queue as well. It worked well. I've appended (what I think are the most important) code-fragments at the end. I don't know if I would do it the same way again; this was years ago. Regards, Marc van Dongen > initQueue :: Ix i => (LinkedList s i v) -> [(i,v)] -> ST s (Maybe i,Maybe i) > initQueue _ [] > = return (Nothing,Nothing) > initQueue marks ((i,v):ivs) > = writeArray marks i (Nothing,Nothing,Just v) >> > a2q marks i i ivs > addToQueue :: Ix i => > (LinkedList s i v) > -> (Maybe i) > -> (Maybe i) > -> [(i,v)] > -> ST s (Maybe i,Maybe i) > addToQueue marks fst lst [] > = return (fst,lst) > addToQueue marks Nothing_ ijrs > = initQueue marks ijrs > addToQueue marks (Just fst) (Just lst) ijrs > = a2q marks fst lst ijrs > a2q :: Ix i => > (LinkedList s i v) > -> i > -> i > -> [(i,v)] > -> ST s (Maybe i,Maybe i) > a2q _ fst lst [] > = return (Just fst,Just lst) > a2q marks fst lst ((i,v):ivs) > = readArray marks i >>= \(_,_,mbv) -> > case mbv of > Nothing -> readArray marks lst >>= \(jpred,_,jv) -> > writeArray marks lst (jpred,Just i,jv) >> > writeArray marks i (Just lst,Nothing,Just v) >> > a2q marks fst i ivs > _ -> a2q marks fst lst ivs > delFromQueue :: Ix i => > (LinkedList s i v) > -> (Maybe i) > -> (Maybe i) > -> [i] > -> ST s (Maybe i,Maybe i) > delFromQueue _ jfstjlst[] > = return (jfst,jlst) > delFromQueue marks jfst@(Just fst) jlst@(Just lst) (i:is) > = readArray marks i >>= >\(jpred,jsucc,_) -> > writeArray marks i (Nothing,Nothing,Nothing) >> > case jpred of > Nothing -> case jsucc of > Nothing -> return (Nothing,Nothing) > (Just s) -> readArray marks s >>= \(_,s',r') -> > writeArray marks s (Nothing,s',r') >> > delFromQueue marks jsucc jlst is > (Just p) -> case jsucc of > Nothing -> readArray marks p >>= \(p',_,r') -> > writeArray marks p (p',Nothing,r') >> > delFromQueue marks jfst jpred is > (Just s) -> readArray marks p >>= \(p',_,r') -> > writeArray marks p (p',jsucc,r') >> > readArray marks s >>= \(_,s',r') -> > writeArray marks s (jpred,s',r') >> > delFromQueue marks jfst jlst is
Re: libraries for Integer
George Russell ([EMAIL PROTECTED]) wrote: [...] : Sorry I can't be more helpful. But there is unlikely to be a simple : answer to the question "Does LIP or GMP multiply numbers fastest?"; : it will depend on how big the numbers are, what platform you are using, : and how much difficult the interface is to use. (GMP is faster if Thanks anyway. [...] Regards, Marc
Re: libraries for Integer
George Russell ([EMAIL PROTECTED]) wrote: : I agree actually. Integer only needs to be an implementation of : multiprecision arithmetic; we shouldn't tie it to GMP. There are : other multiprecision arithmetic packages out there, for example But it is pretty fast. : the LIP package included in NTL :http://www.shoup.net/ntl/ Do you have any data about comparisons with this or other packages? Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 903578 University College Cork, NUIC | Fax: +353 21 903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: Type signatures in instance declarations?
Koen Claessen ([EMAIL PROTECTED]) wrote: [snip] : * Why can one not have a type declarion in the export : list of a module? Common practice for many people : is to put these types in comments now (which is really : dangerous, since the types might change but not the : comments). I would love to see type signatures in export lists. It may also allow you to export a function implemented with a universal type signature for a certain specific type. > module Foo( same :: Int -> Int -> Bool ) where > same :: a -> a -> Bool > same = (==) Regards, Marc
Re: Type signatures in instance declarations?
George Russell ([EMAIL PROTECTED]) wrote: : Why are these illegal? I appreciate that they can't give useful information : to the compiler, which knows the type already from the class, but in my : opinion they are still useful to the maintainer, because they serve as : a reminder of the type. : I agree. I posted a similar comment one or two years ago. Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 903578 University College Cork, NUIC | Fax: +353 21 903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: ServiceShow class for messages
S.D.Mechveliani ([EMAIL PROTECTED]) wrote: [ error messages printing their aguments ] Printing the argument of a function as part of an error message may lead to infinite error messages. It may even lead to several calls to error which all have to be shown. I don't think a compiler will ever be able to detect such infinite situations and should therefore not be allowed to automatically print arguments because the quality of the messages will be very bad. Also I just looked up the following in the language definition: A call to error terminates execution of the program and returns an appropriate error indication to the operating system. It should also display the string in some system-dependent manner. When undefined is used, the error message is created by the compiler. This suggests that a call to error should result in termination. Perhaps I am missing something. Regards, Marc
Re: Ratio: (-1:%1) < (-1:%1)?
Lennart Augustsson ([EMAIL PROTECTED]) wrote: : > The definition : > of (*) in the Prelude has to be clumsy because it cannot : > assume that this will the case because users can construct : > their own Ratios. : How can a user create his own Ratio? The % operation does the : GCD reduction, as does every other operation that creates a Ratio. It is not possible. As I replied before but you may not have received it yet, I was wrong in assuming that one could use :%. Again, sorry about the confusion. Regards, Marc van Dongen
Re: Ratio: (-1:%1) < (-1:%1)?
D. Tweed ([EMAIL PROTECTED]) wrote: : If you haven't loaded any modules then hugs is in `module scope' of : prelude and it's possible. If you do, eg, :l List then you end up in that : module scope and it's no longer allowed. That's exactly what happend. I ran hugs and typed in (1:?2). I was just trying to find out why a module with :%'s in it was not accepted by hugs. Thanks for the explanation. Regards, Marc
Re: Ratio: (-1:%1) < (-1:%1)?
Lennart Augustsson ([EMAIL PROTECTED]) wrote: : > I am not quite sure how to express this in Haskell : > terms but here it goes anyway: Why is :% in Ratio : > not hidden? : What?!? Of course :% is hidden. It's always been hidden. : If it isn't it's a bug in your implementation or a (new) bug : in the repotr. It's always been hidden before; exposing it would : be a grave error. Hmm. I must have missed something. My hugs (1.4) allows it. I was assuming that Haskell did allow it. As it turns out my latest ghc doesn't. That's cool. Thanks. Sorry for the confusion. Regards, Marc
Re: Ratio: (-1:%1) < (-1:%1)?
Jerzy Karczmarczuk ([EMAIL PROTECTED]) wrote: [...] : First of all: at least in Hugs (:%) is *not* exported by : the Prelude. : : So, it is hidden, and a sane, well educated gentleman would : not procreate a fraction with negative denominator. That is the point I am trying to make. Not all people are gentle. Another thing is that gentlemen normally ensure a gcd of 1 for numerator and denominator. The definition of (*) in the Prelude has to be clumsy because it cannot assume that this will the case because users can construct their own Ratios. : The form (1:%-1) is an abomination. Perhaps less than (1:%0), : but anyway. But how to have a low-level efficiency and a : direct access to data structures, and the respect of all : mathematic constraints? In principle we could have a polar : representation of complexes: (r,theta), and somebody really : funny could put a negative r inside. I haven't looked at that. But if it is not the intended way to use these things at least it should be documented. : And then somebody really sad would cry that (r,theta) is equal : but not really, to (r,theta+2PI). But they are equal. However, see my previous point about documentation. [...] Regards, Marc -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Ratio: (-1:%1) < (-1:%1)?
Dear group, Maybe others have mentioned this as well but I can't recall having seen this anywhere. I am not quite sure how to express this in Haskell terms but here it goes anyway: Why is :% in Ratio not hidden? By allowing a user program to construct elements of the form (a:%b) one can create objects which lead to inconsistencies if each of the following hold: (1) for all a: not (a < a); (2) for all a, b and c: if a < b and b < c then a < c. (3) for all a: if a <= b and b <= a then a == b Now Ratio defines (<=) and (<) as (x:%y) <= (x':%y') = x * y' <= x' * y (x:%y) < (x':%y') = x * y' < x' * y According to these definitions and using pseudo notation the following must hold: (-1:%1) < (0:%1) < (1:%-1) == (-1:%1), The last equality follows from (3) and the fact that: (1:%-1) <= (-1:%1) and (-1:%1) <= (1:%-1). Using (2) it now follows that (-1:%1) < (-1:%1) which according to (1) should not be true. According to the language definition (1:%-1) != (-1:%1). Personally I think that built-in data types should obey (1), (2) and (3). Maybe I am missing something. Any comments? Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: Q: Library for (efficient:-) join and projection
Hi Tom, : Hi Marc. : : The Haskell type system can't express a polymorphic natural join. I can understand that. : Even the Trex extension to Hugs doesn't quite manage it. That's why : I'm keen on a further extension: symmetric record catenation. :-) What I need (and I hacked a quick and dirty version) is something with the following functionality: data Table variable value = Table [variable] [[value]] naturalJoin :: (Ord a,Ord b) => Table a b -> Table a b -> Table a b projection :: (Ord a,Ord b) => Table a b -> [a] -> Table a b : Also, the attached message may be relevant. Thanks! [...] Regards, Marc van Dongen
Q: Library for (efficient:-) join and projection
Dear group, I don't want to reinvent this wheel and was wondering if anybody knows of a publicly available library with functions allowing for the creation of tables, the computation of natural joins and projections of these tables (and possibly more). Any pointer will be greatly appreciated. Regards, Marc van Dongen -- Marc van Dongen, CS Dept | phone: +353 21 4903578 University College Cork, NUIC | Fax:+353 21 4903113 College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
Re: Enum instance for Ratio
George Russell ([EMAIL PROTECTED]) wrote: : Marc van Dongen wrote: : > I think it has to respect the implicit order which : > is defined by toEnum and fromEnum. But I may be wrong. : Well that's the current definition. But if you have toEnum and fromEnum : that's much stronger than Ord. I don't like toEnum/fromEnum anyway; it makes Neither do I. : no sense for Doubles. I don't like those either:-) Regards, Marc
Re: Enum instance for Ratio
George Russell ([EMAIL PROTECTED]) wrote: : > data Human = Woman | Man : Hmm maybe. But then are you going to make succ Woman = Man or succ Man = Woman?? I think it has to respect the implicit order which is defined by toEnum and fromEnum. But I may be wrong. : It seems to me that in any case you are going to upset people. By defining successor or predecessor? : Humans are a special case because there are only two ways of ordering the : sexes, and both are controversial. If we have :data Colour = Red | Blue | Yellow : and want to make Colour an instance of Enum, then to consistently define [..] : you need to make arbitrary choices. If you're going to arbitrarily choose an : enumeration it doesn't seem unreasonable to me to arbitrarily choose an ordering : as well. I have to think about that. Regards, Marc
Re: More on randoms
Jerzy Karczmarczuk ([EMAIL PROTECTED]) wrote: [...] : the Haskell standard libraries offer only the basic integer RNG, : which will force all the users to reconstruct the needed reals, : this is not extremely painful, but anyway. : I would love having 'next' returning reals as well... : And vectors (with decently uncorrelated elements). Etc. Yes please. But do change the word vector into [Integer]. [...] Regards, Marc van Dongen
How much MB do I need
To compile a large Haskell program. I am compiling at the moment without optimization and 55 MB of heap. Still ghc complains that the heap is too small. Any suggestions? Marc van Dongen [EMAIL PROTECTED]
happy related question
Dear all,
Could someone explain me why the following does not work?
Any help is *greatly* appreciated. If I can't find out
what causes this problem, I'll have to program in c and
use yacc & lex for the next 2.5 years :-(
Sincerely,
Marc van Dongen
[EMAIL PROTECTED]
*** tmp.ly **
> {
> module Tmp(happyError) where
> }
> %name test
> %tokentype { Token }
> %token
> var { TokVar }
> %newline { '\n' }
> %%
> Test :: { String }
> Test:{ "" }
Test: var{ "" } -- also won't work
> {
> happyError :: Int -> [Token] -> a
> happyError i _ = error ("Parse error in line " ++ show i ++ "\n")
> data Token = TokVar
> }
*** happying and ghcing *
> happy tmp.ly
> ghc -c tmp.hs
"tmp.hs", line 41:
Couldn't match the type `Token' against `Char'.
Inside two case alternatives:
... TokVar -> cont 2
... '\n' -> happyNewToken action (ln + 1) tks
Compilation had errors
* tmp.hs
-- parser produced by Happy Version 0.8
module Tmp(happyError) where
data HappyAbsSyn
= HappyTerminal ( Token )
| HappyAbsSyn1 ( String )
type HappyReduction =
Int
-> ( Token )
-> HappyState ( Token ) ([HappyAbsSyn] -> ( String ))
-> Int
-> [ Token ]
-> [HappyState ( Token ) ([HappyAbsSyn] -> ( String ))]
-> [HappyAbsSyn]
-> ( String )
action_0,
action_1 :: Int -> HappyReduction
happyReduce_1 :: HappyReduction
action_0 1 = happyGoto action_1
action_0 _ = happyReduce_1
action_1 3 = happyAccept
action_1 _ = happyFail
happyReduce_1 = specHappyReduce_0 1 reduction where {
reduction (
happyRest)
happy_var_lineno = HappyAbsSyn1
( "" ) : happyRest}
happyNewToken action ln []
= action 3 3 (error "reading EOF!") (HappyState action) ln []
happyNewToken action ln (tk:tks) = case tk of
TokVar -> cont 2
'\n' -> happyNewToken action (ln + 1) tks
where cont i = action i i tk (HappyState action) ln tks
test = happyParse
happyError :: Int -> [Token] -> a
happyError i _ = error ("Parse error in line " ++ show i ++ "\n")
data Token = TokVar
-- Start of Happy Template (version 0.8)
happyParse tks = happyNewToken action_0 (1::Int) tks [] []
-- All this HappyState stuff is simply because we can't have recursive
-- types in Haskell without an intervening data structure.
data HappyState b c = HappyState
(Int -> -- token number
Int -> -- token number (yes, again)
b -> -- token semantic value
HappyState b c -> -- current state
Int -> -- line number
[b] -> -- rest of tokens
[HappyState b c] ->-- state stack
c)
-- Ok, Here are the action functions.
happyAccept _ _ _ _ _ _ [ HappyAbsSyn1 ans ] = ans
happyFail _ _ _ ln tks _ _ = happyError ln tks
happyShift new_state i tk st ln tks sts stk =
happyNewToken new_state ln tks (st:sts) (HappyTerminal tk:stk)
happyGoto action j tk st = action j j tk (HappyState action)
-- happyReduce is specialised for the common cases.
specHappyReduce_0 i fn j tk st@(HappyState action) ln tks sts stk
= action i j tk st ln tks (st:sts) (fn stk ln)
specHappyReduce_1 i fn j tk _ ln tks sts@(st@(HappyState action):_) stk
= action i j tk st ln tks sts (fn stk ln)
specHappyReduce_2 i fn j tk _ ln tks (_:sts@(st@(HappyState action):_)) stk
= action i j tk st ln tks sts (fn stk ln)
specHappyReduce_3 i fn j tk _ ln tks (_:_:sts@(st@(HappyState action):_)) stk
= action i j tk st ln tks sts (fn stk ln)
happyReduce i k fn j tk st ln tks sts stk
= action i j tk st' ln tks sts' (fn stk ln)
where sts'@(st'@(HappyState action):_) = drop (k::Int) (st:sts)
-- Internal happy errors:
notHappyAtAll :: Int -> a
notHappyAtAll i = error ("Internal Happy error in reduction ( "
++ show i ++ " )")
-- end of Happy Template.
