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RE: Happy and Macros (was Re: ANNOUNCE: Happy 1.10 released)
by Simon Marlow 11 May '01

11 May '01

S. Alexander Jacobson writes: > I am not a parsing expert, but given the recent discussion on > macros, I > have to ask: why use happy rather than monadic parsing? > Monadic parsing > allows you to avoid a whole additional language/compilation > step and work > in Hugs (where you don't have a makefile). What does Happy > buy you here? It buys you (a) speed, (b) confidence that your grammar is non-ambiguous, and (c) familiar BNF notation. On the down side, as you point out, you lose Haskell's abstraction facilities. I'd be willing to sacrifice (c) in order to write parsers in Haskell, but I don't think there's a combinator library that matches Happy in terms of speed (disclaimer: I haven't exhaustively tested them all, but given the tricks Happy does I'd be surprised). AFAIK none of the combinator libraries gives you (b). Cheers, Simon

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RE: sharing datatypes : best practice ?
by Taesch, Luc 11 May '01

11 May '01

do u isolate just the datatype, or a few related with, in a very small file (header like, i would say) or some basic accessor function with it ? isnt it leading to massiv quantities of small files ? > -----Original Message----- > From: Jan Kort [mailto:kort@science.uva.nl] > Sent: Donnerstag, 10. Mai 2001 16:36 > To: Taesch, Luc > Cc: 'haskell(a)haskell.org' > Subject: Re: sharing datatypes : best practice ? > > > "Taesch, Luc" wrote: > > > > i ve developped a datatype in a module P, and another > module will use it, and most probably a few others, and its > quite central to the apps Im building. > > > > what is the best organisation ? > > > > -import module P everywhere > > - isolate this datatype in a module, which would be > imported everywhere ?(very "include like") > > - merging the module around this datatype ? > > > > this last option is not a good option here as : > > - this would be too big > > - P is generated by Happy. > > Hi Luc, > Isolating the datatype in a module is what I always do. > Only "Main.hs" calls the happy parser and just about > every module uses the datatype, so it makes sense to > separate them. > > Jan > This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. CREDIT SUISSE GROUP and each of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorised to state them to be the views of any such entity. Unless otherwise stated, any pricing information given in this message is indicative only, is subject to change and does not constitute an offer to deal at any price quoted. Any reference to the terms of executed transactions should be treated as preliminary only and subject to our formal written confirmation.

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haskell wiki wiped ?
by Taesch, Luc 11 May '01

11 May '01

i tried to acces the hasakell wiki ? it s just all blank. has it been purged ? i remember having seen some idioms ... This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. CREDIT SUISSE GROUP and each of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorised to state them to be the views of any such entity. Unless otherwise stated, any pricing information given in this message is indicative only, is subject to change and does not constitute an offer to deal at any price quoted. Any reference to the terms of executed transactions should be treated as preliminary only and subject to our formal written confirmation.

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Fundeps and class contexts
by Marcin 'Qrczak' Kowalczyk 10 May '01

10 May '01

Would allowing this make sense? class C a b | a -> b class C a b => S a I want to simulate a particular "class synonym" (with four superclasses instead of one C here) where the type 'b' is uninteresting for its users. Currently I have to write class C a b | a -> b class C a b => S a b | a -> b and use f :: S a b => T(a) instead of f :: S a => T(a) even though T(a) usually doesn't contain b. If it does, I would write f :: (S a, C a b) => T(a) -- __("< Marcin Kowalczyk * qrczak(a)knm.org.pl http://qrczak.ids.net.pl/ \__/ ^^ SYGNATURA ZASTÊPCZA QRCZAK

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Re: Happy and Macros (was Re: ANNOUNCE: Happy 1.10 released)
by cwitty＠newtonlabs.com 10 May '01

10 May '01

"S. Alexander Jacobson" <alex(a)shop.com> writes: > I am not a parsing expert, but given the recent discussion on macros, I > have to ask: why use happy rather than monadic parsing? Monadic parsing > allows you to avoid a whole additional language/compilation step and work > in Hugs (where you don't have a makefile). What does Happy buy you here? I've used Happy instead of parser combinators because I wanted the additional global error-checking. I believe that the standard implementations of parser combinators will allow you to specify an ambiguous grammar, and return one of the multiple possible parses, without warning. Carl Witty

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sharing datatypes : best practice ?
by Taesch, Luc 10 May '01

10 May '01

i ve developped a datatype in a module P, and another module will use it, and most probably a few others, and its quite central to the apps Im building. what is the best organisation ? -import module P everywhere - isolate this datatype in a module, which would be imported everywhere ?(very "include like") - merging the module around this datatype ? this last option is not a good option here as : - this would be too big - P is generated by Happy. this look very much like a OO/non OO debate, which I dont want to spawn again. I can suppose its a FAQ like question. any good pointer ? whats the best practice around ? thanks Luc This message is for the named person's use only. It may contain confidential, proprietary or legally privileged information. No confidentiality or privilege is waived or lost by any mistransmission. If you receive this message in error, please immediately delete it and all copies of it from your system, destroy any hard copies of it and notify the sender. You must not, directly or indirectly, use, disclose, distribute, print, or copy any part of this message if you are not the intended recipient. CREDIT SUISSE GROUP and each of its subsidiaries each reserve the right to monitor all e-mail communications through its networks. Any views expressed in this message are those of the individual sender, except where the message states otherwise and the sender is authorised to state them to be the views of any such entity. Unless otherwise stated, any pricing information given in this message is indicative only, is subject to change and does not constitute an offer to deal at any price quoted. Any reference to the terms of executed transactions should be treated as preliminary only and subject to our formal written confirmation.

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The definition of lhsfun in the report
by Mads Lindstrøm 10 May '01

10 May '01

I'am confused about the "funlhs" production, in "Report on the programming Language Haskell 98" of the 1st February 1999. In the report one of the "funlhs"-productions is (see page 127): funlhs -> var apat {apat} That is a <var> followed by one to many <apat>. But you can have functions like this: fun :: Int fun = 17 That is without any patterns to match, so why is the rule not ? funlhs -> var {apat} That is a <var> followed by zero to many <apat>. I will be very happy for an answer to my question. _______________________________________________________ Send a cool gift with your E-Card http://www.bluemountain.com/giftcenter/

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Class RealFrac: round
by Rijk-Jan van Haaften 09 May '01

09 May '01

Hello, While I were writing a RealFrac implementation for BigDouble's (for high-precision computations) I found a strange implementation of round in the standard prelude (from the haskell definition): round x = let (n,r) = properFraction x m = if r < 0 then n - 1 else n + 1 in case signum (abs r - 0.5) of -1 -> n 0 -> if even n then n else m 1 -> m The strange case is if signum (abs r - 0.5) is 0: such numbers are round to the nearest EVEN integer. In mathematics, computer science (the studies I'm doing) and physics, as far as I know, it is usual to round such numbers up, rather than to the nearest integer. For example: Number Hugs Math 0.5 0 1 1.5 2 2 -3.5 -4 -4 6.5 6 7 Why did the Haskell designers choose this behaviour? Thanks in advance, Rijk-Jan van Haaften

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RE: Class RealFrac: round
by Joe Bowers 09 May '01

09 May '01

I'm not one of the implementors, but this sort of behavior can reduce error in fields where X.5 is a common result- a rule like "The nearest even integer" moves upward half the time and downward half the time- hopefully cancelling itself out. Or maybe they had other reasons... Joe > -----Original Message----- > From: Rijk-Jan van Haaften [mailto:rjchaaft@cs.uu.nl] > Sent: Wednesday, May 09, 2001 8:06 AM > To: haskell(a)haskell.org > Subject: Class RealFrac: round > > > Hello, > > While I were writing a RealFrac implementation for BigDouble's (for > high-precision computations) I found a strange implementation of > round in the standard prelude (from the haskell definition): ... > The strange case is if signum (abs r - 0.5) is 0: > such numbers are round to the nearest EVEN integer. In mathematics, > computer science (the studies I'm doing) and physics, as far as I > know, it is usual to round such numbers up, rather than to the nearest > integer. For example: > > Number Hugs Math > 0.5 0 1 > 1.5 2 2 > -3.5 -4 -4 > 6.5 6 7 > > Why did the Haskell designers choose this behaviour? > > Thanks in advance, > > Rijk-Jan van Haaften > > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell >

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RA position @ Heriot-Watt Univ. in program analysis
by Joe Wells 09 May '01

09 May '01

Research Assistant Position Useful Logics, Types, Rewriting, and Applications (ULTRA) Group Computing and Electrical Engineering Department Heriot-Watt University Edinburgh, Scotland, UK A research assistant (RA) position is available on an EPSRC-funded project directed by Joe Wells. The position is in the ULTRA (Useful Logics, Types, Rewriting, and Applications) group in the Department of Computing and Electrical Engineering at Heriot-Watt University in Edinburgh, the capital of Scotland. The RA should either already have skills in some of the following areas and be interested and able to learn about several others: * type systems, especially those with intersection and union types, * static analysis of computer programs, * constraint solving, * higher-order programming languages, * programming language semantics, design, and/or implementation. The RA will be expected to help build, document, test, maintain, distribute, and support significant software components for performing modular program analysis. The RA will also be expected to aid in writing scientific reports on the work done. The position is initially for 1 year, with possible extensions depending on performance and funding. The salary will be commensurate with qualifications and experience. It is preferred that the RA already has or is just about to complete a Ph.D. in a relevant discipline within Computer Science. To formally apply for this position, please do the following: * Arrange for 3 letters of reference to be sent. * Send the following yourself: + your complete curriculum vitae, + a brief statement of your research accomplishments and interests and why you think you would be a good match for the job, + web pointers to or paper copies of at most 3 publications of yours which you think are relevant, and + contact details for the people writing your letters of reference. If you send documents electronically, please use public, standard, and non-proprietary formats. Microsoft Word documents will be rejected. Applications or inquiries should be directed to Joe Wells at: web: http://www.cee.hw.ac.uk/~jbw/ e-mail: jbw(a)cee.hw.ac.uk fax: +44 131 449 3834 post: Computing and Electrical Engineering Department Heriot-Watt University EDINBURGH EH14 4AS GREAT BRITAIN

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