August 2001 - Haskell

2 points on language. Continuing
by S.D.Mechveliani 24 Aug '01

24 Aug '01

To my recent message >> (2) >> I wrote in the BAL paper that meaningful standard algebraic >> categories (classes) may, in principle, help the compiler to >> optimize programs using the properties related to the category >> names (associativity, commutativity ...). >> [..] >> I kept in mind implicitly that as soon as these categories enter a >> library standard their names can also be added to the >> _key words of a language_. >> In this way the compiler is enabled to use the relevant properties. >> There remains a question of expressions like _|_ + 1 === 1 + _|_, >> but this is another matter, maybe, a matter of flags for the compiler >> and language version. Dylan Thurston <dpt(a)math.harvard.edu> responds on 23 Aug 2001 > One question I have here is, how much are compilers prepared to take > advantage of such knowledge? (Also, does it really belong in the > compiler? > In, e.g., FFTW, all this is optimized by a user program rather than the > compiler.) I'm slightly skeptical: it's not entirely obvious how to > take proper advantage of commutativity/associativity, and this seems like > something I'd want to program directly rather than trust the compiler > to do. But I haven't thought about this much; other opinions? I am skeptical too. Anyway, if a compiler `knows' the word CommutativeRing, knows that by definition, CommutativeRing requires associativity, commutativity ..., observes the instance CommutativeRing T for some type T in some program, sees further expr = (2*a + b) - (a+a) :: T and sees the language version (compiler) flag -fignore-bottom, (something of this sort) then, has it right to convert expr --> b :: T ? To my mind, there is something more in this than intension. In practice, the users do not write explicitly such expressions as expr. But they write them implicitly, by applying functions in special cases, for example, one has f(x,y) and applies f(x,2*x) ... I do not ask compilers to exploit now this possibility. Only noted that a meaningful category organization provides, in principle, room for such optimization. Am I missing something? For I can mistake. Further, to my >> (1): >> As I wrote earlier, Haskell instances cannot model such domains as >> the residue ring Integer/(n), when n changes dynamically. >> This is why the BAL library applies the sample argument approach, >> and this somewhat complicates the program meaning. >> >> Now, we observe in the Aldor manual (http:/www.aldor.org), >> Section 7.8: >> `` >> Zmod(n: Integer) : Ring with { if prime? n then Field; } >> == >> Integer add { if prime? n then {inv (x: %) : % == ...} } >> >> Z_n, the domain of integers modulo n, is always a Ring. However, >> if n is prime, then Z_n is also a Field, meaning that it should >> provide a multiplicative inverse for nonzero values. In an `add' >> expression, a definition which appears in the consequence of an >> `if' expression is said to be a conditional definition ... >> '' Dylan Thurston <dpt(a)math.harvard.edu> writes > Z_n indeed sometimes supports additional operations. But how is the > user expected to use these operations in a type-safe, statically checked > way? Any use of 'inv' for Z_n will necessarily involve a run-time > check on n to see whether it is prime. > [..] I believe, Aldor checks some types at run-time. And it has types as values. In fact, the above Zmod is a _function_ that takes values in a type called Ring. Each value Zmod(n) is a domain (abstract data type) of type Ring. Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

4 3

2 points on language
by S.D.Mechveliani 24 Aug '01

24 Aug '01

To my > Anyway, if a compiler `knows' the word CommutativeRing, > [..] > expr = (2*a + b) - (a+a) :: T > > and sees the language version (compiler) flag -fignore-bottom, > (something of this sort) then, has it right to convert > > expr --> b :: T > ? > [..] D. Tweed <tweed(a)compsci.bristol.ac.uk> writes > On a purely pragmatic note ( :-) ) these optimisations can't necessarily > be safely used in three of the four most common cases, namely Int, Float > and Double because of the restricted range of intermediates. > [..] Int, Float, Double are not supposed to be provided with the CommutativeRing instance. And most common cases are, to my mind, different: Integer, Rational, (Integer, Rational), Polynomial Integer ... Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

1 0

MTV'02: Call for Papers
by Miroslav Velev 24 Aug '01

24 Aug '01

Microprocessor Test and Verification (MTV'02) January 21-22, 2002, Austin, Texas, USA: http://ece.tamu.edu/MTV/ Deadline for submission of abstracts: October 26, 2001 P.S. Note the special topic on optimizing SAT procedures for application to testing and formal verification.

1 0

RE: ghc on win2k ...
by Simon Peyton-Jones 24 Aug '01

24 Aug '01

| I think you need cygwin to install/run it. | | >Has anyone gotten ghc operative over win2k? I couldnt even get | >the v4.08 | >installshield to work for me (it installed fine but then ghc | >just wouldnt | >do anything, not even an error report). No longer! You don't need cygwin, or indeed *anything*. Just install GHC and away you go. (On the other hand, if you *do* have cygwin, GHC won't intefere with it.) Nevertheless, you have good reason to not know this: it's not on GHC's web page. Only readers of the Haskell list will have seen Reuben's announcement (below). We expect to make a new release of GHC, 5.02, at the end of next week, just before ICFP. It fixes many bugs in the release below -- but none the less, the one below is fine for most purposes. Simon ========================================= I've updated the test Windows InstallShield of GHCi 5.01 available from http://www.haskell.org/ghc/dist/5.00.2/ghc-5-01.exe (There's no link to it on the web site) In case you missed the previous announcement, this is a test release, but seems fairly stable (I use it all the time). It has the following features: * GHCi: now you can use GHC interpretively under Windows. You can just run the InstallShield, and double-click on GHCi to get going. * Complete install: everything you need to use GHC is included; Cygwin is no longer required; also, unlike recent 4.08.2 releases, it doesn't interfere with any Cygwin installation you may already have Changes from the previous test release, "Zarjaz": * Now installs in Program Files by default (supports paths containing spaces). * Installs the profiling libraries and imports (the previous test release included them, but for mysterious reasons they weren't actually installed). Also note that as one user found, the supplied gcc doesn't like identifiers containing top-bit-set characters, so if you want to use them you must use the native code generator.

1 0

2 points about language
by S.D.Mechveliani 23 Aug '01

23 Aug '01

Dear haskellers, I suggest you the two notes on the Haskell language: (1) it is desirable to accommodate such features of Aldor language as types as values and dependent types (2) the properties of operations, like associativity, commutativity ..., can be handled by `usual' Haskell, to some extent. (1): As I wrote earlier, Haskell instances cannot model such domains as the residue ring Integer/(n), when n changes dynamically. This is why the BAL library applies the sample argument approach, and this somewhat complicates the program meaning. Now, we observe in the Aldor manual (http:/www.aldor.org), Section 7.8: `` Zmod(n: Integer) : Ring with { if prime? n then Field; } == Integer add { if prime? n then {inv (x: %) : % == ...} } Z_n, the domain of integers modulo n, is always a Ring. However, if n is prime, then Z_n is also a Field, meaning that it should provide a multiplicative inverse for nonzero values. In an `add' expression, a definition which appears in the consequence of an `if' expression is said to be a conditional definition ... '' But Aldor is non-functional, strict, has a bit of `garbage' in the language, has only one implementation, and this one is not free-with-source. Also I am not sure that the above example will really work in the existing Aldor implementation. Further, there exists a fully commercial Axiom program, which can be considered as a large nonstandard algebraic library for Aldor. This library is certain recommendation for the language. It will be good for Haskell, or any language of its type, to extend and drift towards Aldor, but with preserving functionality and elegance. I always thought (naively) that `unsolvability' of types is a fiction. Typically, types and instances resolve at the run-time. But the compiler has to try each time to resolve at compile time as much as possible. (2) I wrote in the BAL paper that meaningful standard algebraic categories (classes) may, in principle, help the compiler to optimize programs using the properties related to the category names (associativity, commutativity ...). On the other hand, people write now and then, that they consider such possible properties only as intended, saying that the language does not provide room for their explicit usage (the latter was also said by the referee of this paper). It occurs to me now that there may be certain misunderstanding. I kept in mind implicitly that as soon as these categories enter a library standard their names can also be added to the _key words of a language_. In this way the compiler is enabled to use the relevant properties. There remains a question of expressions like _|_ + 1 === 1 + _|_, but this is another matter, maybe, a matter of flags for the compiler and language version. Regards, ----------------- Serge Mechveliani mechvel(a)botik.ru

3 2

RE: ghc on win2k ...
by Konst Sushenko 23 Aug '01

23 Aug '01

I think you need cygwin to install/run it. >-----Original Message----- >From: Amit Garg [mailto:amitji@cs.utexas.edu] >Sent: Thursday, August 23, 2001 1:38 PM >To: haskell(a)haskell.org >Subject: ghc on win2k ... > > >Hi. > >Has anyone gotten ghc operative over win2k? I couldnt even get >the v4.08 >installshield to work for me (it installed fine but then ghc >just wouldnt >do anything, not even an error report). > >Thanks for any help on this. >-Amit. > >------------------------------------------------------------------- >Amit Garg | Office: 3.108 Taylor Hall >Graduate Student | Phone : (512) 232-7869 >Computer Sciences | Res : 2910 Medical Arts #304 >University of Texas at Austin | Phone : (512) 482-8329 > Homepage: http://www.cs.utexas.edu/~amitji >------------------------------------------------------------------- > > > >_______________________________________________ >Haskell mailing list >Haskell(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell >

1 0

ghc on win2k ...
by Amit Garg 23 Aug '01

23 Aug '01

Hi. Has anyone gotten ghc operative over win2k? I couldnt even get the v4.08 installshield to work for me (it installed fine but then ghc just wouldnt do anything, not even an error report). Thanks for any help on this. -Amit. ------------------------------------------------------------------- Amit Garg | Office: 3.108 Taylor Hall Graduate Student | Phone : (512) 232-7869 Computer Sciences | Res : 2910 Medical Arts #304 University of Texas at Austin | Phone : (512) 482-8329 Homepage: http://www.cs.utexas.edu/~amitji -------------------------------------------------------------------

1 0

Re: Enforcing Strict Evaluation
by Dean Herington 22 Aug '01

22 Aug '01

Someone privately asked a question concerning my module "DeepSeq" for "deep" strict evaluation: > > module DeepSeq where > > > class DeepSeq a where > > deepSeq :: a -> b -> b > > deepSeq = seq -- default, for simple cases > > ... > > > instance DeepSeq Ordering where > > > instance DeepSeq Integer where > > instance DeepSeq Int where > > instance DeepSeq Float where > > instance DeepSeq Double where > > Are these supposed to be empty? Yes. These, plus the instances for (), Bool, and Char, are "simple cases" where the default method definition (deepSeq = seq) suffices. Now realizing that the "where" keyword is optional when there are no accompanying declarations, I think it would be preferable to omit the "where" keyword to indicate that the absence of declarations is intentional. Dean

1 0

ICQ on Haskell?
by Haoran Un 22 Aug '01

22 Aug '01

Hi everyone, I was wondering if anyone had written (or atempted to write) ICQ in Haskell? My honours thesis project is extending Manuel Chakravarty's GTK+HS by placing a more functionally-friendly wrapper over the top - iHaskell. (see: http://www.cse.unsw.edu.au/~chak/haskell/gtk/#iHaskell and http://www.cse.unsw.edu.au/~haoranun/ihaskell/) Anyway, in an attempt to have a real-world application written with iHaskell, I thought I'd write yet another ICQ clone, but in Haskell. As the point of the project is to have a nice GUI, I was wondering if anyone had the underlying networking code written that I could perchance appropriate and use for my program. Even half-written but documented code could be useful, and I'd like o see what people have. All of the stuffed would be GPLed, and you'd get your name in the credit (for whatever immortality that's worth). Thanks, Haoran ==================================================== 'Teacher, what is the greatest commandment in the Law?' Jesus replied: '`Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment. And the second is like it: `Love your neighbor as yourself'' - Matthew 22:36-39 ====================================================

1 0

haskell on palmOS?
by Matthew Tarnawsky 21 Aug '01

21 Aug '01

Hi, I've heard that there may have been some work done on porting hugs to the palm platform, but have been unable to dig up anything on my own. So, I figured I'd ask here - anyone have any information on this topic that they would care to share? Thanks in advance... -Matthew

1 0