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(no subject)
by Phil Haymen 09 Feb '02

09 Feb '02

hi,I have a function, using list comprehension to pick out the head and last elements from a list of lists and output this into a list without duplicates. It doesn't work. I want to know what is the error. function :: [[Int]] -> [Int] function seg = nub (concat([head s, last s | s <- seg]) __________________________________________________ Do You Yahoo!? Send FREE Valentine eCards with Yahoo! Greetings! http://greetings.yahoo.com

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RE: efficiency question
by Konst Sushenko 09 Feb '02

09 Feb '02

(moved to haskell-café) I ran Hal's code on my computer, and with test2 I get a stack overflow (so I had to use +RTS option for it to finish). test1 does not overflow stack (of standard size, I mean without +RTS). Which implies that test2 uses more stack space than test1. why would it use more stack if not because of laziness? konst > -----Original Message----- > From: Hal Daume III [mailto:hdaume@ISI.EDU] > Sent: Friday, February 08, 2002 4:35 PM > To: Jorge Adriano > Cc: Konst Sushenko; haskell(a)haskell.org > Subject: Re: efficiency question > > > I agree that it's the overhead of (,), but I don't see why > there would be > any overhead for doing this. > > -- > Hal Daume III > > "Computer science is no more about computers | hdaume(a)isi.edu > than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume > > On Sat, 9 Feb 2002, Jorge Adriano wrote: > > > On Friday 08 February 2002 23:52, Hal Daume III wrote: > > > I've tried using a strict fold: > > > > > > foldl' f a [] = a > > > foldl' f a (x:xs) = (foldl' f $! f a x) xs > > > > > > but that has no effect (or minimal effect). > > > > That wouldn't work even if if laziness is the problem > because that would only > > cause the elements of the list to be evaluated to head > normal form, the > > elements of the pair would not be evaluated so you'd have a > 'suspension of > > (minus and plus) operations'. > > > > instead of > > > (\x (a,b) -> (x+a,x-b)) > > try > > > (\x (a,b) -> (((,) $! x-a)$! x-b) ) > > > > I just noticed that you were the one who sent me the DeepSeq module. > > This is the kind of place where I want to use it. > > Instead of $!, try $!!. > > > > > > And Konst Sushenko wrote: > > >>My guess is that it is due to the laziness of the > addition/subtraction > > >>in (,) > > > > Seems to me like lazyness is not the right guess because > both functions Hall > > first posted were lazy. So I think it's just the overhead > of applying (,) > > besides (+) and (-) in each step. Do I make sense or am I > missing something? > > > > J.A. > > > >

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character syntax
by Ian Zimmerman 09 Feb '02

09 Feb '02

I am new to the language (coming from ML) and I am sorry if my first post turns out to be a flamebait, but I can't help it: Why in the world did the designers of Haskell permit the ' character to be both a prime (part of identifiers) and the single-character quote? Didn't they realize what they were doing to would-be intelligent editors? Or were they just a bunch of rabid ed users? Has anyone found a way to deal with this in Emacs, _correctly_? That is, among other things, '(' should be ignored for sexp parsing... -- Ian Zimmerman, Oakland, California, U.S.A. GPG: 433BA087 9C0F 194F 203A 63F7 B1B8 6E5A 8CA3 27DB 433B A087 The world has taken on a thickness of vulgarity that raises a spiritual man's contempt to the violence of a passion. Baudelaire

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Re: efficiency question
by Jorge Adriano 09 Feb '02

09 Feb '02

> I'd say that's because in the second case you also got to apply the (,), > besides the (+)/(-) constructor during the transversing... > Am I right? opss... I meant to write: the (,) constructor besides the (+)/(-)... J.A. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: efficiency question
by Jorge Adriano 08 Feb '02

08 Feb '02

> I'd say that's because in the second case you also got to apply the (,), > besides the (+)/(-) constructor during the transversing... > Am I right? opss... I meant to write: the (,) constructor besides the (+)/(-)... J.A.

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Re: win32 stand alone binaries?
by Sigbjorn Finne 08 Feb '02

08 Feb '02

Brett Morgan brett(a)pulse.itd.uts.edu.au writes: > > Is it possible to build win32 stand alone binaries using cygwin hosted > ghc tools? Hi, that's what you get by default these days, GHC doesn't rely on cygwin (nor the applications it produces). If you _really_ want to, you could compile up the GHC sources to use cygwin though, of course. hth --sigbjorn

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Re: character syntax
by C.Reinke 08 Feb '02

08 Feb '02

> > Second, this argument would be easier to accept if there in fact were > > an equally innovative tool capable of providing all the editing > > goodies Emacs normally does, for Haskell. But I don't know of one, > > even now, 10 years or so after Haskell's birth. Well, it was one of the happier accidents in programming language history that Lisp was implemented and released before it received a concrete syntax. But Haskell isn't built on s-expressions. Simon M. says that syntax highlighting for Haskell is quite doable, and Haskell modes for other editors seem to support that claim, as others have pointed out. So I wonder whether what once was a very innovative tool is in the process of becoming just another legacy. I'm relatively happy with my editor, as far as editors go. What features (editing goodies) are you referring to? > .. There was recently a PhD position advertised > on the list in the area of refactoring functional programs; I'd be > surprised if whoever does that doesn't eventually end up with a GUI > (whether inherited from somewhere else or written as part of the project). Postdoc, actually. Although, once we have someone in place on that position, it would also be nice to complement our project with a PhD candidate working on refactoring in another functional language (Erlang, say), sufficiently different from both Haskell and from the oo/imperative languages for which refactoring support is now becoming more and more common. As for innovation in program editing, the idea (and problem) is not so much awareness of lexical syntax (syntax highlighting) or editing at the level of abstract syntax (for those with unhappy memories of structure editors: we want syntax-aware editors, not syntax-directed ones), but making editing tools more aware of language semantics (static semantics, at least). As for GUIs, we would like to avoid getting into editor wars, and we would rather spend our time on the refactoring side than on implementing YAE, yet another editor. Simon and I happen to use the same YFE (your favourite editor), but we know that there's a big group of Haskell users who wouldn't be very pleased if they had to switch from TOE (that other editor) to YFE, just to make use of our refactoring tool (note that I'm silently ignoring AOE, all other editors here;-). And both groups would be very unhappy if they had to go from their own powerful, all-purpose editor to whatever we could hack up while we should be doing other things. It's too early to say how things will pan out in the end, but we'd like to start with a separate refactorer, with a well-defined interface, and bindings to that interface for both YFE and TOE. As you suggest, the refactorer will have rather more information about the program than might easily be displayed via YFE/TOE/ETC, so we might need a separate GUI at some point. We'll see.. IYSWIM?-) Claus Refactoring Functional Programs http://www.cs.ukc.ac.uk/people/staff/sjt/Refactor/

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RE: character syntax
by Simon Marlow 08 Feb '02

08 Feb '02

> itz> All this taken together, I mean, _really_, is the lexical > itz> structure of Haskell a botch, or what? > > Jon> No. Innovative. All the problems described in this thread reflect > Jon> unwarranted assumptions inherited in emacs. It's plainly possible > Jon> to parse Haskell, and not hard either. > > First, parsing of a complete program (eg. by a compiler) is quite > different from parsing a buffer that is being edited by a human. The > latter is hard, even for fairly well-specified languages. > Irregularities only make it harder. For syntax highlighting you only need to lexically analyse the buffer, not parse it. Haskell's lexical syntax is parseable by regular expressions, which means it shouldn't be hard to plug a syntax highlighter for Haskell into just about any editor. I don't understand why you say that parsing a buffer being edited by a human is hard - perhaps doing incremental lexing is slightly harder than whole-file lexing, but not that much harder. The "state" of a Haskell lexer can be represented with a little trickery by an integer, so it isn't hard to cache the lexer's state at the beginning of each line. I did this once as an experiment when I added Haskell syntax highlighting to one of the KDE editors (I forget which). The problem is not Haskell, it's emacs. Emacs's syntax highlighting has fairly deeply-wired-in assumptions about C-like languages (eg. last I looked you still couldn't support nested comments properly in font-lock). Cheers, Simon

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win32 stand alone binaries?
by Brett Morgan 08 Feb '02

08 Feb '02

Is it possible to build win32 stand alone binaries using cygwin hosted ghc tools? I know in some ways this is sacriligous to the many unix die hards out there (myself included) - but some of the algorithm's i'm contemplating could possibly turn out to be useful for the "unwashed masses" if a wimp binary could be produced. And I really don't want to go back to c++ for reasons i'm sure most people here are familiar with... brett -- email: Brett.Morgan(a)uts.edu.au phone: 0416-241-898 magic: 153 2 8 105 225 You just come along with me and have a good time. The Galaxy's a fun place. You'll need to have this fish in your ear. Q: What is the shortest lie in computing? A: It works. -- Matthias Felleisen

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Re: compiling hdirect
by Sigbjorn Finne 05 Feb '02

05 Feb '02

Johannes Goetx info(a)polirami.de writes: > ... > gcc -O -mno-cygwin -mwin32 -c mkNativeInfo.c -o mkNativeInfo.o > mkNativeInfo.c:0: malformed option `-D __WIN32__-DWIN32' ... > > malformed option `-D __WIN32__-DWIN32' > > Where can I change this? I could not find a file containing this > option string. Hi, you're using a version of gcc with a broken 'specs' file. Locate the specs file inside your cygwin(?) install tree & change the portion of the "*cpp:" section which expands -mwin32 and -mno-cygwin to the following: %{mwin32|mno-cygwin:-DWIN32 -D_WIN32 -D__WIN32 -D__WIN32__ -DWINNT } i.e., add a space after -DWINNT and the '}' This issue will soon go away, as the use of -mwin32 in GHC's fptools/ tree is in the process of being nuked. hth --sigbjorn

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