- Haskell - Haskell.org

./configure
by Christian Maeder 06 Dec '02

06 Dec '02

Hi, when installing ghc and hugs under SuSE linux 8.1 I got "configure: error: can not guess host type; you must specify one" It worked after I added "--host=i386-linux" Christian

1 0

Re: Completeness of pattern matching
by ketil＠ii.uib.no 06 Dec '02

06 Dec '02

ketil(a)ii.uib.no (Ketil Z. Malde) writes: > Malcolm Wallace <Malcolm.Wallace(a)cs.york.ac.uk> writes: > > > Ingo Wechsung <iw(a)contexo.de> writes: > >> I wonder if the compiler could check, if all possible combinations have > >> been checked in a pattern match. > > > In ghc, use the compile-time option -fwarn-incomplete-patterns > > Is there a warning to warn if a block is delimited (or not) with a mix > of tabs and spaces? Or somehow otherwise warn against dangerously > looking layout? Talking about warnings, it is probably patently stupid to put {-# OPTIONS -fglasgow-exts -package lang #-} at the top of my Main.lhs. But why does GHC (5.04-1) fail to find any of my imports as a consequence? Bug? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

1 0

RE: stupid strictness question
by Simon Marlow 05 Dec '02

05 Dec '02

> Now, we define: > > > data SMaybe a = SNothing | SJust !a deriving Show > > Now, we run: > > *Strict> Just (undefined::Int) > Just *** Exception: Prelude.undefined > *Strict> Just $! (undefined::Int) > *** Exception: Prelude.undefined > *Strict> SJust $! (undefined::Int) > *** Exception: Prelude.undefined > *Strict> SJust (undefined::Int) > SJust *** Exception: Prelude.undefined > > I can't figure out why this last one is different from the > one before it, or the one before that. This one is a GHCi (not GHC) bug. You may have seen this message while loading the source containing the strict constructor definition: WARNING: ignoring polymorphic case in interpreted mode. Possibly due to strict polymorphic/functional constructor args. Your program may leak space unexpectedly. which means that GHCi essentially ignored the strictness flag on the polymorphic field of the SJust constructor. To work around the bug, you can compile that module with GHC. The good news is that this bug will be fixed in the next major release. Cheers, Simon

1 0

stupid strictness question
by Hal Daume III 04 Dec '02

04 Dec '02

i know i know, this has been asked a million times, but i was searching through the archives with no success, so i figured i'd bug you guys. according to the report: A declaration of the form data cx => T u1 ... uk = ... | K s1 ... sn | ... where each si is either of the form ! ti or ti, replaces every occurance of K in an expression by (\x1 ... xn -> ( ((K op1 x1) op2 x2) ... ) opn xn) where opi is the lazy apply function $ if si is of the form ti, and opi is the strict apply function $! (see Section 6.2) if si is of the form !ti. Pattern matching on K is not affected by strictness flags. so. we define: > data L = L Int deriving Show > data S = S !Int deriving Show and, as expected, we get: *Strict> L undefined L *** Exception: Prelude.undefined *Strict> L $! undefined *** Exception: Prelude.undefined *Strict> S undefined *** Exception: Prelude.undefined Now, we define: > data SMaybe a = SNothing | SJust !a deriving Show Now, we run: *Strict> Just (undefined::Int) Just *** Exception: Prelude.undefined *Strict> Just $! (undefined::Int) *** Exception: Prelude.undefined *Strict> SJust $! (undefined::Int) *** Exception: Prelude.undefined *Strict> SJust (undefined::Int) SJust *** Exception: Prelude.undefined I can't figure out why this last one is different from the one before it, or the one before that. Interestingly, Hugs disagrees (the previous was with ghc 5.04.1): Strict> Just (undefined::Int) Just Program error: {undefined} Strict> Just $! (undefined::Int) Program error: {undefined} Strict> SJust $! (undefined::Int) Program error: {undefined} Strict> SJust (undefined::Int) Program error: {undefined} Which is what I expected. Can someone clarify here? - Hal

1 0

Re: Design patterns in Haskell
by Chris.Angus＠Lawson.com 04 Dec '02

04 Dec '02

I spent an awful lot of time doing a brain-dump into these pages and am a bit dissapointed that they seemed to have dissappeared without trace. Were these archived anywhere Keith Wansbrough <Keith.Wansbrough(a)cl.cam.ac.uk> Sent by: haskell-admin(a)haskell.org 03/12/2002 18:02 To: matt hellige <matt(a)immute.net> cc: haskell(a)haskell.org, (bcc: Chris Angus/Lawson) Subject: Re: Design patterns in Haskell > size. while there's really no substitute for experience, i really > believe we could benefit from some patterns. There was a list of design patterns for Haskell on the Wiki (back in the days when it worked): http://haskell.org/wiki/wiki?CommonHaskellIdioms --KW 8-) -- Keith Wansbrough <kw217(a)cl.cam.ac.uk> http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory. _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell

2 1

Oops, another H'98 report error.
by Malcolm Wallace 04 Dec '02

04 Dec '02

I know it is no far too late to do anything about it, but I just discovered another error in the Haskell'98 Libraries Report. The Time module exports all but one of the fieldnames of the CalendarTime datatype, bizarrely omitting ctSec. Regards, Malcolm

1 0

RE: ANNOUNCE: GHC version 5.04.2 released
by Simon Marlow 04 Dec '02

04 Dec '02

> ============================================================== > The (Interactive) Glasgow Haskell Compiler -- version 5.04.2 > ============================================================== > > We are pleased to announce a new patchlevel release of the Glasgow > Haskell Compiler (GHC), version 5.04.2. This is a bugfix-only > release. For all the changes since 5.02.3, see the release notes: > > > http://www.haskell.org/ghc/docs/latest/users_guide/release-5-04.html Oops, that URL should be http://www.haskell.org/ghc/docs/latest/html/users_guide/release-5-04.htm l Cheers, Simon

1 0

Re: The Haskell 98 Report
by cwitty＠newtonlabs.com 04 Dec '02

04 Dec '02

"Claus Reinke" <claus.reinke(a)talk21.com> writes: > So, as a small token, I've revised my original plan and will now buy one > of the printed versions (I shall also place higher priority on submitting > to JFP in the future;-). Let's support forward-looking publishers! > > Thanks, Simon, and thanks, Conrad Guettler & CUP! I agree totally (I wasn't going to buy a copy, but now I will). Please let us know when the book becomes available through online bookstores... Thanks, Simon and Conrad! Carl Witty

1 0

AW: slide: useful function?
by Markus.Schnell＠infineon.com 03 Dec '02

03 Dec '02

Thanks for the comments. It seems the function is not really needed (at least not predefined), although I use it fairly often. > Read more in > > T Uustalu, V Vene. The dual of substitution is redecoration. > In K Hammond, S Curtis, eds, Trends in Functional Programming > 3, pp 99-110. Intellect, > Bristol / Portland, OR, 2002. - .ps.gz, 46K (© Intellect) > > http://www.cs.ioc.ee/~tarmo/papers/sfp01-book.ps.gz , > > if you want to be bothered with categorical nonsence ;-) There's too much mathematics in it, I'm only an engineer... ;-) Thanks, Markus -- Markus Schnell, Infineon Technologies AG

14 21

Mathematics and Software Engineering (was slide: useful function? )
by Markus.Schnell＠infineon.com 03 Dec '02

03 Dec '02

> > There's too much mathematics in it, I'm only an engineer... ;-) Perhaps I should rephrase: > There's too much mathematics in it, I'm not a mathematician > reminds of what I think is one of the biggest problems with > conventional > software development: the lack of appreciable mathematics in the > specification, design, coding, or implementation of programs. In this While this is surely true, I think, there is also a lack of communication between software engineers. Civil, Mechanical or Electrical Engineers have well-established plans, while software engineers have not (see http://fmc.hpi.uni-potsdam.de/) One should not forget, that many practical problems are not solvable by a rigorous mathematical approach. German reading people may have a look at http://fmc.hpi.uni-potsdam.de/research/literature/wendt_1998-kommunikationsp roblem_der_informatiker.pdf, where some problems are pointed out (with an edge to it). > sense there is a huge contrast between conventional software > development > practice and other engineering disciplines. Definitely. But software development is probably not old enough... It's like the difference between somebody bying some Radio Shack stuff and putting it together until it works, and an engineer making informed decisions for layout and choice of elements for a circuit. This informedness relies partly on mathematics, but at least as much on experience and pragmatics. Most software people are still bying Radio Shack stuff... (and isn't it easy?) > I was once an electrical > engineer, and I used lots of mathematics (not just in school, but in > industry), and I know that most other engineering disciplines > also use a So you know that to use diracs and fourier you don't necessarily need to understand what functionals are about. Likewise, it's not necessary to understand category theory to use monads and the like. > lot of mathematics. One of the things I like about FP is that it > demands more mathematical sophistication of its practitioners, which, > contrary to some opinions, I think is a Good Thing. I'm fully with you there, but - as someone already pointed out - I don't want to need a math major to read a paper regarding programming. This doesn't mean there is something wrong with these papers, it's just that I wished there would be more accessible versions. Hope to got my point across, Markus -- Markus Schnell, Infineon Technologies AG

2 1