- Haskell-Cafe - Haskell.org

Re: finding ....
by Pixel 20 Mar '02

20 Mar '02

Lennart Augustsson <lennart(a)augustsson.net> writes: > Thank you for making my point. All these are indeed examples of broken code. > (Not because it's Perl. :) ok, sorry for trying. I won't change my code and you won't change your mind.

3 2

Re: finding ....
by D. Tweed 20 Mar '02

20 Mar '02

[Moved to haskell-cafe] On Tue, 19 Mar 2002, David Sankel wrote: > > *everytime* about race conditions. (of course using > > this existFile before > > creating a temporary file is wrong, but existFile > > has *many* other > > applications) > > Could someone post an example of the creation of a > temporary file where race conditions are important? IIRC one of the classic issues is --------- myscript wants to create a temporary file called /tmp/storedStuff being half-careful, checks file doesn't exist (*) miniscule delay occurs creates a new file called /tmp/storedStuff --------- creating a new file generally deletes a file of the same without causing any errors since this is often the desired semantics All this is ok until a malicious person manages to get ln -s /home/sankel/reallyImportantUnbackedupData /tmp/storedStuff in the interval denoted by (*) ___cheers,_dave_________________________________________________________ www.cs.bris.ac.uk/~tweed/|`...heat generated by its microprocessors will email:tweed@cs.bris.ac.uk|slope upward exponentially, reaching the power work tel:(0117) 954-5250 |density of a nuclear reactor before 2010'-Intel

2 1

RE: finding ....
by Konst Sushenko 19 Mar '02

19 Mar '02

Moved to haskell café I do not have a code example, but how about a system that compiles different (and say independent) software projects in parallel, and which uses the same code to create temporary files needed for compilation? konst > -----Original Message----- > From: David Sankel [mailto:camio@yahoo.com] > Sent: Tuesday, March 19, 2002 6:38 PM > To: Pixel; Lennart Augustsson > Cc: haskell(a)haskell.org > Subject: Re: finding .... > > > --- Pixel <pixel(a)mandrakesoft.com> wrote: > > Lennart Augustsson <lennart(a)augustsson.net> writes: > > > > > > Diego Yanivello wrote: > > > > > > > > > hi, is there (in Haskell) a function like > > existFile :: FilePath -> > > > > > IO (Bool) ? Thanks! > > > > > > Using such a function is generally a bad idea > > because of race conditions. > > > > however, real world programs use those tests since > > you don't need to care > > *everytime* about race conditions. (of course using > > this existFile before > > creating a temporary file is wrong, but existFile > > has *many* other > > applications) > > Could someone post an example of the creation of a > temporary file where race conditions are important? > > Thanks, > > David J. Sankel > > __________________________________________________ > Do You Yahoo!? > Yahoo! Sports - live college hoops coverage > http://sports.yahoo.com/ > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

1 0

Re: Gaussian Integers
by Ashley Yakeley 19 Mar '02

19 Mar '02

(moved to Cafe) At 2002-03-19 03:33, dominic.j.steinitz(a)britishairways.com wrote: >I've already declared Gaussian a as being of class Eq so why does it need >to be told again? No you haven't. You've declared 'Eq a => Eq (Gaussian a)' -- 'Gaussian a' is Eq if 'a' is, not 'Eq (Gaussian a)'. Try this instance Eq a => Num (Gaussian a) where ... ...and actually looking at your code, I think you want this: instance Num a => Num (Gaussian a) where ... -- Ashley Yakeley, Seattle WA

1 0

partial application
by Cagdas Ozgenc 19 Mar '02

19 Mar '02

Greetings. Is there a reason why partial application cannot be applied in arbitrary order? Was it a technical difficulty in the design of Haskell? Or is it just following beta reduction rigorously? Thanks

9 10

Reading and processing data file
by Ramachandran M 18 Mar '02

18 Mar '02

I'm working on an assignment at my uni that requires me to prompt the user for an input and to locate that item in a data file. For example, if the user enters a flight no. of IC009, the program should locate that particular record in the file and output the flight's origin and destination. How should I go about writing this in Haskell? Any pointers would be greatly appreciated. Thanks. _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com

1 0

Partial application on any argument(s) regardless of argument order (Was: Re: partial application)
by Dimitre Novatchev 18 Mar '02

18 Mar '02

Koen Claessen koen(a)cs.chalmers.se wrote: > Cagdas Ozgenc wondered: > > | Is there a reason why partial application cannot be > | applied in arbitrary order? Was it a technical > | difficulty in the design of Haskell? Or is it just > | following beta reduction rigorously? > > Alastair David Reid answered: > > | Haskell doesn't dictate any particular evaluation > | order. If you look at the name of the Haskell report, > | it calls Haskell a "non-strict" language not a "lazy" > | language. > > Somehow I do not think that Cagdas was talking about > evaluation order at all. I think he referred to the > following: Suppose I have a function f which is defined to > have 3 arguments: Partial application on any subset of arguments regardless of their order has been implemented in the FXSL functional programming library and is described here: http://www.topxml.com/xsl/articles/df/ Cheers, Dimitre Novatchev. __________________________________________________ Do You Yahoo!? Yahoo! Sports - live college hoops coverage http://sports.yahoo.com/

1 0

Re: partial application
by C.Reinke 18 Mar '02

18 Mar '02

> ..I was thinking of the following syntax. I orginally had the > idea for C++, where you can't do partial application at all. ? FC++: Functional Programming in C++ http://www.cc.gatech.edu/~yannis/fc++/ (I wouldn't be defending C++ otherwise, but its set of things you can't do at all must be a lot smaller than in other languages;-) They seem to support the _ notation, btw. Laurent Dami had a lambda-calculus variant that allowed for partial application by name instead of by position (amongst several other interesting features:) http://cui.unige.ch/~dami/publis.html Claus -- Research Opportunity: Refactoring Functional Programs (UKC) Closing date: Friday 22 March 2002 !! http://www.cs.ukc.ac.uk/vacancies_dir/r02-24.html

1 0

Re: partial application
by Peter G. Hancock 18 Mar '02

18 Mar '02

Apropos of section notation, don't forget flip, alias the C combinator. It allows you to express partial applications "to the next argument but one" is in operator section notation. We can express (usually horribly) any affine lambda-abstraction with flip, (.), id and const. Peter Hancock

1 0

Re: Hiring Haskell programmers
by John Hughes 15 Mar '02

15 Mar '02

> Depends where you are, I guess. In Sydney, it would be > easy. We are teaching Haskell to about 1500 first-year > students every year. > Melbourne University is teaching similar numbers (perhaps slightly less; probably more than 1000) of first-year students Haskell every year. -- Nick Nethercote njn25(a)cam.ac.uk Goodness me, we're only teaching 160 here in Gothenburg! I feel inadequate! However, we're teaching 20 or so a year to an advanced level, so I reckon there are around 100 really skillful Haskell programmers in Gothenburg by now. That should be enough for a while... John Hughes

1 0