Re: [Haskell-cafe] Haskell vs Ruby as a scripting language
Hi Also, I recommend looking into embedding YHC. I have not had a chance to use it yet, but it looks like it is a better fit to an interpreter-only embedding situation than GHC--with GHC, you are getting a lot more than you seem to be asking for. I would want to compile code as well. Compile bits of code 100 lines at a time and load them back into my app for execution. Does YHC compile and how efficiently? Yhc can happily compile code and run it. You'll probably pay a factor of 2-8 times slower than GHC, depending on what the code does. The entire Yhc binary distribution on Windows is 8Mb, of which 6Mb is the compiler. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monolithic module tool
Hi Chad I think what you are after is Haskell All-In-One: http://www.cs.utah.edu/~hal/HAllInOne/index.html As it happens, since that date Yhc has moved on to the point where: yhc Main.hs -linkcore loadCore Main.yca = writeFile Main.hs . coreHaskell Will get you a similar result - but with desugaring applied as well. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Portable implementation of unsafeCoerce
Hi Alfonso, Reading the sources of Lava (a Haskell Hardware Description DSL) I run into this definition ... unsafeCoerce :: a - b Is this actually equivalent to the infamous unsafeCoerce# ? Yes, see the comment in the haddock documentation for unsafePerformIO: http://haskell.org/ghc/docs/latest/html/libraries/base/Foreign.html#v%3AunsafePerformIO Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] External Core
Hi Ricky, For the last year I've been working on a program to translate between Haskell and Java. Originally this was for my third year dissertation to contribute towards my Masters in computer science at Sheffield University, UK. I have been given the opportunity to continue this project and have become interested in using the Core representation as an intermediary language. You might be interested in Yhc.Core - its like GHC's Core, but is simpler, untyped and (in my opinion) better supported. http://haskell.org/haskellwiki/Yhc/API/Core We already have a Haskell - Javascript convertor written using this, so your type of application is certainly doable using what we have already. There are quite a few users of Yhc.Core already, and everyone has had nice things to say about it :) If you have any specific Yhc.Core questions feel free to ask away Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] how to calculate the sum of list of lists?
Hi Miranda, How to calculate the sum of list of lists in Haskell? What do you mean by this? What is the value of a list? If you mean sum the numbers such that [[1,2],[3,4]] = 1+2+3+4 then you are able to ask two alternative questions - how do i convert a list of lists to a list, and how do i sum a list. Both can be answered by Hoogle: http://haskell.org/hoogle/?q=%5BInt%5D%20-%3E%20Int The list of lists to a list is a bit easier so I'll leave you to solve that one :) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to remove all numbers from a list that are divisible by an integer
Hi Miranda, Now I need to know how to remove all numbers that are divisable by an integer. Is this a homework problem? Is there some bigger goal you are trying to achieve? I tried to use some zipWith...filter and other predefined functions..but I can't really find the right solution :( Can you perhaps show us some of the solutions you tried, so we can see what direction you were going in? It's easy enough to give you the answer, but it's probably beneficial to you if we help you learn these things for yourself. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to remove all numbers from a list that are divisible by an integer
Hi Miranda, filter :: (a - Bool) - [a] - [a] filter p [] = [] filter p (x:xs) = if p 'mod' x then x : filter p xs else filter p xs I tried this, but it doesn't work You are mixing a few things together. First point, mod should be `mod` and not 'mod' - ' means character, ` means infix operator as a name. Second point you can only if test on a Bool, mod returns an Int. Third, filter is an already defined function, if you look up it's source you'll see how you can use this in your program. If you were to hop onto Haskell IRC I'm sure you could get these problems resolved quickly - http://haskell.org/haskellwiki/IRC_channel - you seem to have roughly the basic idea behind the algorithm, its just lots of little details. Perhaps working through a Haskell tutorial would help you clarify these things. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] nested maybes
Hi This is true. Some time ago I swore off the use of fromRight and fromLeft in favor of maybe, and have been forgetting about the other functions in Data.Maybe ever since. I think you mean you swore off fromJust. Unfortunately when people started to debate adding fromLeft and fromRight they decided against logic and consistency, and chose not to add them... Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Boost equivalent
Hi John, Does the Haskell community have an equivalent to C++ community's Boost project with the aim of writing libraries for the eventual inclusion into Haskell? We have: 1) MissingH - a nice staging ground for things that may end up in the base library 2) Library submission process, to add things to the base libraries 3) Hackage - anyone can write a library that anyone can use. I think that covers most uses. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Circular programming (aka time-travel) resources?
Hi Justin, A quick google search turned up a couple of blogs and some papers - but is there more out there? http://news.cs.york.ac.uk/ftpdir/pub/colin/jfp97lw.ps.gz Laziness, circularity and prime numbers all in one :) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is Excel the most used -- and fucntional -- programming lanuage on Earth?
Hi Alexy, Heard that statement recently -- that Excel is a functional programming language, and the most used one -- of any programming languages -- on Earth! Is it true? Are there good examples of typical FP style in Excel? You can't define functions in Excel, hence its not really a functional language. I'd go as far as saying its an expression-based programming language, but that's it. It also has mutable state (if you use circular references) so its not pure. That said, the quote almost certainly comes from this paper (in the title): http://research.microsoft.com/~simonpj/Papers/excel/index.htm Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi My standard solution was to invoke wget, but a Haskell solution would be nicer. For my purpose following redirects etc. isn't required, so thanks very much for your help. I will be releasing this function as part of a library shortly, so will be giving you credit for your help! Good god, no! The code was merely meant to illustrate how a really basic HTTP GET might work. It certainly doesn't deal with a lot of the additional cases, like redirects and resource moves, and non-standards-compliant HTTP servers. I'm no HTTP expert, so for all I know this example code is likely non-standards-compliant too. It really only works for a very straightforward text file GET, and there's no exception or error handling, or any of the more interesting cases. But at the same time its the best solution available without going to much pain and C libraries. I would love something more robust and equally simple, but haven't found it. The library I am writing is one to parse and extract information from HTML documents, the fact that I can now download web pages merely makes the examples I give more interesting - its not the fundamental essence of the library. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi So yes, we need to fix it. There's people to do it. Now we just need social factors to kick in and make it happen! We really do! The inability to get a file off a website is quite depressing given that the hard bit should be designing an API, but that anyone could do that for openURL in about 5 minutes. is there a mailing list haskell-cafe@ or twiki to direct these efforts? http://haskell.org/haskellwiki/Http Haskell already has all the infrastructure to run this project, all it needs is the people with the time. I have no time to help, but really want to use the end result :) Where is the http strike team when you need them? ;) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC-Cygwin
Hi Daniil My desire is simple. I want GHC-Cygiwn. Why? I find Cygwin really really horrible and avoid it where possible. I was just wondering what advantages you get from having GHC-Cygwin? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: binary: high performance, pure binary serialisation
Hi Conrad, If the data header stores the alignment/size/endianness, then there's no reason for the data to be unportable. The normal get* instances (not get*host) could suffice for reading. That requires the stream to have a header. Which means that any arbitrary slice within the ByteString is not equal - the first one contains essential information which isn't available anywhere else. It seems like a lot of complexity, defining multiple parameterised file types, when the simple case is probably neater and cheaper in terms of both runtime and developer time. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] proposal: HaBench, a Haskell Benchmark Suite
Hi What about using darcs as a benchmark? I heard people say it's slow. The undercurrent is that it's slow because it's written in Haskell. Its slow because some algorithms are O(stupid value). Some operations (I've been told) would take 100's of years to terminate. That has nothing to do with Haskell. Also its not written in Haskell, its written in GHC-Haskell. This benchmark suite should try where possible to be a Haskell benchmark. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi Daniel, Adding in hPutStrLn h (Connection: close\r\n) or hPutStrLn h (Connection: keep-alive\r\n) as appropriate should sort that. Works like a charm. This is responding with a 302, the resource has been found but is temporarily at another location indicated in the responses Location header. So, now you'll have to start parsing responses. In this case the Location header is www.cs.york.ac.uk/public.php I didn't get as far as getting the 302, but it works now. The cheap and cheerful solution might be to invoke cURL. My standard solution was to invoke wget, but a Haskell solution would be nicer. For my purpose following redirects etc. isn't required, so thanks very much for your help. I will be releasing this function as part of a library shortly, so will be giving you credit for your help! Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Numeric Class Problem
Hi Dennis, (/) :: Fractional a = a - a - a div :: Integral a = a - a - a Basically, use / on Float/Double like things, and div on Int/Integer like things: If you do want to use double like things throughout, then using fromInteger around the place will help: floor (fromInteger j * (fromInteger n / fromInteger p2n)) This converts easy value from an Integer to a number thing, which will allow you to treat it like a Double/Float thing. If you are using Int (rather than Integer) you might need fromInteger (toInteger x) around the place. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Converting Types to Terms
Hi, I have got loads of requests to allow Hoogle to do this, usually something like if you search [Bool] - [Bool] it should suggest map not, or something - combining functions into the one you want. Unfortunately the search space would be huge for even the smallest library. Worse still, the second you allow id :: a - a, you have an infinite number of matching terms. Some work I have seen which seems related to what you are asking is: http://www.cs.ioc.ee/tfp-icfp-gpce05/tfp-proc/14num.pdf Systematic search for lambda expressions by Susumu Katayama. Thanks Neil On 1/28/07, Stefan O'Rear [EMAIL PROTECTED] wrote: On Sun, Jan 28, 2007 at 09:11:33PM +0100, Klaus Ostermann wrote: I would like to have a program that can synthesize programs for a given type, composing only functions from a given library. For example, suppose my library has isZero :: Int - Bool map :: (a - b) - [a] - [b] and :: Bool - Bool - Bool fold :: (a - b - a) - a - [b] - a True :: Bool (.) :: (b - c) - (a - b) - a - c Why just (.) ? I also assume your logic has modus ponens (curry howard: application) then I want to ask, say, for a program of type [Int] - Bool and get as answer (fold and True) . (map isZero) However, with none of these approaches I managed to do anything with list functions. What else is available (besides Djinn and De-Typechecker)? Are lists a problem? In general, what are the practical and theoretical limits of these program synthesizers? Are there any overview papers for this topic? A system (with the full axioms of intuitionist logic) would be much more likely to answer your query with \_ - True . Not very helpful, eh? Lists are recursive types, and it is very easy for a list calculus to lose strong normalization. Without strong normalization, any nontrivial query will be answered with 'undefined'. Not helpful. The only other system I know of is my short theorem prover (on the wiki); it has no architectural reason to not allow list functions, but it has many shallow reasons - slow, obfuscated, doesn't currently track proofs, doesn't currently support higher kinds. Not likely to be usable. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the best way to understand large programs?
Hi Haddock generates interface documentation. That's only appropriate for libraries, isn't it? Wrong, its very useful for normal programs as well. That along with a nice HsColour generated source links with Haddock and you can navigate the code just a bit quicker. Having a Hoogle database for a large program is also handy for figuring out where things are and what they do - especially when the program has introduced new custom data types. Some sort of module dependancy graph would also be handy, but I'm not sure any program can yet produce that kind of information. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi Alistair, Is there a simple way to get the contents of a webpage using Haskell on a Windows box? This isn't exactly what you want, but it gets you partway there. Not sure if LineBuffering or NoBuffering is the best option. Line buffering should be fine for just text output, but if you request a binary object (like an image) then you have to read exactly the number of bytes specified, and no more. This works great for haskell.org, unfortunately it doesn't work as well with the rest of the web universe. With www.google.com I get: Program error: handle: IO.hGetChar: illegal operation With www.slashdot.org I get: 501 Not Implemented returned www.msnbc.msn.com works fine. Any ideas why? Are there any alternatives to read in a file off the internet (i.e. wget but as a library) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi Daniel Note that I haven't tried this, or the rest of Alistair code at all, so the usual 30 day money back guarantee doesn't apply. It certainly won't handle redirects. Thanks, it certainly gets more things, but has a nasty habit of taking a very long time in Hugs on certain URLs: research.microsoft.com/, www.cs.york.ac.uk/ And on some urls, ie http://research.microsoft.com/~simonpj/, it still ends up with IO.hGetChar: illegal operation Any ideas why? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: binary: high performance, pure binary serialisation
Hi I also fear that the existing script does not handle types with more than 256 constructors correctly. While uncommon, those are not unrealistic. Feel free to send in a patch. All it needs to do is check if there are more than 2^8 constructors and if so encode the tag in a Word16 rather than Word8. I've already fixed this and sent some new code to you. As long as you have less than 4 billion constructors you should be fine now. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] basic field questions
Hi
sq = squishiness $ Table {colour = Black, weight=1, height= 2}
main = putStr $ show sq
squishiness is just translated to:
squishiness :: Furniture - Double
squishiness (Chair _ _ x) = x
squishiness _ = error doh
main: No match in record selector Main.squishiness
Hence this is a pattern match error (runtime), not a type error
(compile time). There are people working on extending the types to
catch this kind of thing, and also people working on static checkers
to catch patter match errors [1] and people working on annotations to
get this kind of thing [2].
It's not a solved problem yet, but certainly I have a demo checker
that would have spotted this easily.
Thanks
Neil
[1] http://www-users.cs.york.ac.uk/~ndm/projects/catch.php
[2] http://www.cl.cam.ac.uk/~nx200/research/escH-hw.ps
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Re: [Haskell-cafe] Re: [Haskell] [Fwd: Re: Computer Language Shootout]
Hi I have to disagree with this. That is, I don't object to Don's explanation of why the shootout entries degraded in this particular case, but I do think that Andrzej was right to point this out: Perhaps making a collective effort towards benchmarking Haskell programs and analyzing the results in some methodic way could prove helpful? and I think that he *is* pointing out a fundamental issue here. We have the nofib suite, it could do with some attention, but it is (or was) a pretty good performance tester. Maybe it's just me, but as someone who has some amount of experience with implementing optimizations for Haskell, I find it nearly impossible to precisely understand and measure exactly how those optimizations improve (or degrade) program performance. The problem is that something like GHC is very complex, with lots of transformations. When transformations are firing other transformations, which in turn fire other transformations, it doesn't take a great deal to disrupt this flow of optimisation and end up with a result which doesn't accurately reflect the particular change you made. Better knowledge of the end effects on a program isn't necessarily going to translate to better knowledge of the optimisations effect. Maybe if we had a greater number and variety of optimising compilers we'd be able to more freely experiment with optimisation techniques in different settings. At the moment GHC is all there is (with Jhc not ready for mainstream use yet) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] [Fwd: Re: Computer Language Shootout]
Hi Sorry for being unclear. I agree with your comments on GHC, and one thing I was suggesting was that somebody should think about profiling tools for improving our understanding of how those transformations interact with each other, not just profiling tools for understanding the end result. That would be very neat. Another neat trick would be generalising optimisations so that there are fewer and more independant passes, this would make it easier to understand (and is what I was working on for Yhc). I agree that there should be more diversity in compilers, but I think even sticking to GHC, there's a lot that could be done when it comes to improving understanding of just what the optimizer is doing. Anything better than staring at intermediate code would be an improvement, since time spent staring at intermediate code usually is time spent narrowing down the 2 lines out of 1000 that are relevant. Yhc has intermediate code that is substantially more Haskell like, and with the command: loadCore file.ycr = writeFile file.html . coreHtml You can generate an active Html document that lets you explore the Core in a more interactive way - including hyperlinks for function names, syntax hilighting etc. i.e: http://www.cs.york.ac.uk/fp/yhc/Roman.html All of these things make playing with Yhc Core much more fun than playing with GHC Core. There is absolutely no reason you couldn't add all these things to GHC Core, then perhaps you'd save some time when it does come to the examine core level. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A function for Maybes
Hi Alan, Usually, when I have a question like this, I try Hoogle first: http://www.haskell.org/hoogle/?q=%28a+-%3E+b%29+-%3E+Maybe+a+-%3E+Maybe+b Unfortunatly, the right answer (fmap) is on the second page of results. The reason for this is that Hoogle 3 doesn't understand higher-kinded type classes, i.e. Monad and Functor, which means that fmap doesn't match as closely as it should do. Hoogle 4 would give fmap as the first result, I'm pretty sure. (I am really excited for the new version of Hoogle, its supposed to be pretty close to release) Me too, but you'll probably have to wait a few more months yet - but the various components are coming together nicely. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] [Fwd: Re: Computer Language Shootout]
Hi Yhc has intermediate code that is substantially more Haskell like, and with the command: Wow, the core looks really cool! One look and you see it all. I would even rename the local variables to single letters like a,b,c because the cryptic numbers are quite hard to track. This is something coreHtml can do. Also, I'd add more color, like making punctuation marks grey, but that's a very personal taste. Yhc.Core is a big library of useful things to do with Yhc Core. One of them is: uniqueBoundVarsWith :: [String] - CoreExpr - CoreExpr Which replaces the free variables with a list you pick. This means that the transformation you want is a single line: applyBodyCore (uniqueBoundVarsWith (map (:[]) ['a'..])) That will transform a whole Core program, giving you the variables you requested. That's one of the things I like about Yhc.Core, it is a very nice library to use. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] [Fwd: Re: Computer Language Shootout]
Hi Although there may not be a lot of optimizing Haskell compilers, there are compilers for languages similar to Haskell that consistently perform well. One could point to O'caml or others in the ML family, or even more interesting is the case of Clean, whose syntax heavily borrows from Haskell. ML is strict, this makes a big difference. Things that Haskell compilers do easily (inlining) are harder in a strict language. Things that strict languages do easily (unboxing) are harder in Haskell. There are enough differences to make it not a same thing issue. Clean on the other hand is just Haskell with a different syntax. The Hacle project [1] showed that if you convert Haskell to Clean, you can sometimes beat the performance of Haskell code. What do the Clean folks do that has made their compiler so consistently competitive? Is it the abc machine? Frankly I'm amazed that a three stack based virtual machine can be translated into such efficient machine code in register centric CPU architecture. The 3 stacks give a nice computational model of unboxed operations. Maybe this is the thing that allows more effient CPU layout. Supposedly someone is working on a Haskell compiler that will use the clean compiler back end. The Clean team are (or were) working on a Haskell front end for Clean. The Yhc team is working on a Clean back end. I can't believe that Clean is so fundamentally different, even with uniqueness types, that it has an edge in compiler optimization. Uniqueness types does give some extra optimisation potential, such as destructive updates if you can guarantee a variable is only referred to once. But even with that, the language that has impressed me most on the shootout is Clean. Where the Haskell community spends significant time they can beat Clean, but generally the Clean does very well and looks much more idomatic FP than the Haskell. Thanks Neil [1] google hacle ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] No Derived Read for Unboxed Arrays
Hi, I was trying to convert some code from ordinary boxed array to unboxed arrays for performance reasons. However my code ultimately failed because I load a large array saved as a text file using the derived Read, Show mechanism. I found that Read was maybe 30 times slower than the slowest binary serialisation method I could possibly think of. If performance matters to you, and the array is more than a few elements long, switching away from Read/Show should be the first step - before going for unboxed arrays. (But of course, having Read/Show defined for UArray may well be useful, and sounds a good idea) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] No Derived Read for Unboxed Arrays
HI Don (But of course, having Read/Show defined for UArray may well be useful, and sounds a good idea) There's also an instance Binary for UArray. That might be useful? Is there an instance Binary in a released library? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO is not a monad (and seq, and in general _|_)
Hi That's not quite what I was trying to say. (p^~p)-q is equivalent to _|_ in the sense that once you derive/compute (respectively) it, the world in which it exists breaks. I think thats a bit overly harsh view of _|_ to take. The world does not break once you compute _|_ - a _|_ value doesn't allow you to prove/compute anything you couldn't before. While removing _|_ from the language does make some things nicer to reason about, there aren't many corners where _|_ really gets in the way that much - seq being one of those few corners. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO is not a monad (and seq, and in general _|_)
Hi prove/compute anything you couldn't before. While removing _|_ from the language does make some things nicer to reason about, there aren't many corners where _|_ really gets in the way that much - seq being one of those few corners. But that is exactly the problem: `seq` forces _|_ to get into the way, when it normally doesn't. So I'm not clear that trying to fit `seq` into a formalization of Haskell's semantics is the way to go. Agreed, that was the point I was trying to make :) You seemed to be suggesting _|_ was evil (for want of a more precise term) in its behaviour with Haskell. As you seem to say now (and I agree), _|_ is a perfectly useful value, just seq gets in the way. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strings in Haskell
Hi Alexy, Now I'm reading a Haskell book which states the same. Is there a more efficient Haskell string-handling method? Which functional language is the most suitable for text processing? There are the Data.ByteString things, which are great, and have much less overhead. But remember that Haskell is lazy. If you are thinking well I have to process a 50Mb file, remember that Haskell will lazily read and process this file, which substantially reduces the memory requirements so only a small portion will ever be in memory at a time. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Article review: Category Theory
Hi Brian, I've often wondered why seq is the primitive and not $! Would this solve the problem? Is there any solution that would allow excess laziness to be removed from a Haskell program such that Hask would be a category? class Seq a where seq :: a - b - b Then you have a different seq based on the types, and it doesn't go wrong. You would probably want deriving Seq support. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple HTTP lib for Windows?
Hi, I've often wondered the same as the above poster. Something like readWebPage (in the same style as readFile) would be a really handy function. Do no libraries provide this? (if not, can one start providing it? MissingH?) Thanks Neil On 1/18/07, Alistair Bayley [EMAIL PROTECTED] wrote: I'd like to write a very simple Haskell script that when given a URL, looks up the page, and returns a string of HTML. I don't see an HTTP library in the standard libs, and the one in Hackage requires Windows machines have GHC and MinGW to be installed and in the PATH. Is there a simple way to get the contents of a webpage using Haskell on a Windows box? This isn't exactly what you want, but it gets you partway there. Not sure if LineBuffering or NoBuffering is the best option. Line buffering should be fine for just text output, but if you request a binary object (like an image) then you have to read exactly the number of bytes specified, and no more. Alistair module Main where import System.IO import Network main = client www.haskell.org 80 /haskellwiki/Haskell client server port page = do h - connectTo server (PortNumber port) hSetBuffering h NoBuffering putStrLn send request hPutStrLn h (GET ++ page ++ \r) hPutStrLn h \r hPutStrLn h \r putStrLn wait for response readResponse h putStrLn readResponse h = do closed - hIsClosed h eof - hIsEOF h if closed || eof then return () else do c - hGetChar h putChar c readResponse h ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Article review: Category Theory
Hi Isn't _|_ = \x - _|_? _|_ `seq` () = _|_ (\x - _|_) `seq` () = () Whether this is the fault of seq or not is your call... Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Article review: Category Theory
Hi David, For some reason, in Firefox printing those diagrams to a black and white printer gives black for the background. It means that the arrows and annotations are in black on black, not the most readable... Any way to fix that? Perhaps uploading diagrams with white backgrounds, instead of transparent (if that is currently the case) Thanks Neil On 1/16/07, David House [EMAIL PROTECTED] wrote: Hey all, I've written a chapter for the Wikibook that attempts to teach some basic Category Theory in a Haskell hacker-friendly fashion. http://en.wikibooks.org/wiki/Haskell/Category_theory From the article's introduction: This article attempts to give an overview of category theory, insofar as it applies to Haskell. To this end, Haskell code will be given alongside the mathematical definitions. Absolute rigour is not followed; in its place, we seek to give the reader an intuitive feel for what the concepts of category theory are and how they relate to Haskell. I'd love comments from newcomers and experts alike regarding my approach, the content, improvements and so on. Of course, it's on the wikibook, so if you have anything to add (that's not _too_ substantial otherwise I'd recommend discussion first) then go ahead. Thanks in advance. -- -David House, [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Pattern matching
Hi Stefan,
myFunction x@(Constructor1 _*) = ...
myFunction x@(Constructor2 _*) = ...
myFunction x@(Constructor1 {}) =
myFunction x@(Constructor2 {}) =
myFunction2 (Constructor1 _* a _*) = ...
could be possible as long as the pattern is non-ambiguous (in this
case, only one variable with the type of a is present in this
constructor).
In this context a is not a type, but a value, and the non-ambiguous
constraint can get pretty confusing in a case like this. The answer is
to use records:
data Data = Constructor1 {field1 :: Bool, field2 :: Int, field3 :: Int}
myFunction (Constructor1 {field2=a}) = ...
Thanks
Neil
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Re: [Haskell-cafe] HaskellForge?
Hi I.e. cabal + hackage + planet.haskell + weekly news ;) Does hackage actually allow a user to setup a new darcs repo on a remote server? That's about the only thing lacking - for everything else people can just use code.google.com, which is way better than anything any Haskell hacker would ever have time to come up with. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] readFile problem
Hi Stefan, I am writing a network server in haskell. Lately I seem to have introduced a new bug. On Linux, when a client closes the connection to the server, the server dumps core. Are you using any calls to system? Any libraries which may do funky stuff? application.exe: config.xml: openFile: does not exist (No such file or directory) I use readFile to read the config file. I tried to print out the config file after it is read to make sure that it is completely read. I only load this config file exactly once during program initialization. The config is used long before the crash. I printed the current working dir in the exception handler and there is something interesting. Instead of the path to the application, it is \C:\\WINDOWS\\system32. What is the working directory at the begining? Is that really the working directory? The \C at the start isn't the C drive, but some bizare escape code, I think. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] trouble installing greencard -- -fno-prune-tydecls flag ( was Re: trivial function application question )
Hi In the meantime, how about the following: In default non-verbose mode, silently memoize the list of packages that were not found. Then, only if something goes wrong, say something like: The package failed to build. Perhaps the reason is that one of the following packages was not found: That doesn't seem that helpful. On error, give a list of maybe 25 things that are missing, only to find out that you're running GHC 6.4.1 on Windows which no one ever tried before. It's not really narrowing the cause of the error too much anyway. Something like scons does this much much better than Cabal does - it only complains if it finds something you need but don't have. For example, with Yhc you can compile the compiler with GHC, and the runtime with GCC/Visual Studio. Lacking half those dependancies won't give you an error message if you only try to do the right thing. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] trivial function application question
Hi Brad, i have a small problem that will be certainly trivial for almost everyone reading this, i would appreciate a little help If you have trivial problems, its often useful to ask on Haskell IRC (http://www.haskell.org/haskellwiki/IRC_channel) from which my intent is that a be replaced by Z, b by Y etc i am sure there is an elegant way to apply replace to s for all of these argument pairs without composing replace N times myself, but the solution escapes me. In your example all strings are one letter long, is that how this works? If so, then you can simplify the problem significantly to use Char's, and use the following library functions: First off, if you want to apply the same transformation to each item of a list, namely to either replace it or leave it the same. This calls out for map. Secondly you want to do lookups in some sort of table. The lookup function can be very handy here. The lookup function works on associative lists, so you'd need to zip patterns and replace into an associative list. If you really want to operate on strings, rather than characters, then you have to be more clever. Also replace called multiple times probably won't be enough, consider replacing 1 with 2, 2 with 3. If you just call replace multiple times, 1 may well end up at 3, when 2 is more likely to be the right answer. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Composing functions with runST
Hi On the contrary, I think it's an excellent way of learning Haskell. I'm writing a lot of useful Haskell code with only one IO action (interact). I don't think I could reasonably construct an introductory problem that couldn't be solved with it, and I haven't yet found an application for which I've needed more. I think interact is a bit ugly. Most introductory problems are take a small amount of data, do something. In that case using Hugs/GHCi with :main arguments to give in the arguments, getArgs to read them and putStrLn to show the results is a very beautiful and does about all that you need. Very few programs are actually interactive - if they are they should usually get a GUI. As for beginner issues with rank-2 types, I've been learning Haskell for years now, and have never felt the need for a rank-2 type. If the interface for some feature requires rank-2 types I'd call that an abstraction leak in most cases. It certainly means that you can't properly Hoogle for it, can't compile it with Yhc, can't do full type inference etc. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mo' comprehensions
Hi I was solving some programming puzzles today[1], and found myself pining for Map comprehensions. [ ... (key,val) - fromList map, ... ] It isn't really that much more than a straight comprehension would be on a map. By default should a map comprehension let you inspect the values, or the keys, or both? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Combine list of sorted lists
Hi f1 :: [Int] - [[Int]] f1 [] = [] f1 (a:as) = [a] : f1 as f1 is simply a map f3 la lb = let a = head la b = head lb in if sum a = sum b then a : f3 (tail la) lb else b : f3 la (tail lb) Why not use pattern matching to split up la and lb, rather than head/tail? I would have thought the whole function could be written as a nice foldr merge, where merge :: [Int] - [Int] - [Int]. Thats only a guess at the top of my head though, not worked out properly. Is this homework? If so its useful to state when you post the question :) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Combine list of sorted lists
Hi Quan I am not sure how to express f1 with map? how do I say (lambda (ls) (map (lambda (x) (list x)) ls)) in Haskell? map ([]) ? map (:[]), :[] takes a single element and puts it into a list. Some people refer to this as box The final f3 clause can be made a bit neater: f3 la@(a:as) lb@(b:bs) | sum a = sum b = a : f3 as lb | otherwise = b : f3 la bs Additionally, if it was me I'd refer to a:as on the RHS, rather than giving it a name with the @ pattern, but thats a personal question of style. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Idiomatic Haskell equivalent of keyword arguments to functions
Hi Paul,
To make things concrete, the example I'm really thinking of is a send
an email function, which would take a subject, a body, a list of
recipients, optional lists of cc and bcc recipients, an optional
mailserver (default localhost), an optional port (default 25), and
possibly optional authentication details.
Records are your friend.
data Email = Email {subject :: String, body :: String, to ::
[Address], cc = [Address], bcc = [Address], mailserver :: String, port
:: Int}
defaultEmail = Email{subject = No subject, body = , to = [], cc =
[], bcc = [], mailserver = localhost, port = 25}
The user can then go:
sendEmail defaultEmail{subject=Subject here, body = body here, to
= [haskell-cafe], mailserver = server.haskell.org}
Now things which are't specified (port) keep their default value.
The other alternative is:
data EmailParams = Body String
| Port Int
| Mailserver String
...
then:
sendEmail [Body body here, To haskell-cafe, Mailserver
server.haskell.org ...]
I prefer the first, but the second can also be done.
Thanks
Neil
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Re: [Haskell-cafe] Is there a printable copy of the (GHC) library references anywhere?
Hi Paul, You're right - if I think about it, I'm not really looking for the documentation, but more a paper or article which is a tour of the GHC standard library. A tour of the Prelude: http://undergraduate.csse.uwa.edu.au/units/230.301/lectureNotes/tourofprelude.html Only a few of the standard libraries are useful unless you are doing something specific. i.e. Data.Maybe is generally useful, but Control.Monad.State is only useful if you are using a state monad. If someone wrote a tour of Data.List/Data.Maybe as well as a few common functions out of Control.Monad that would probably make a nice companion to a tour of the prelude. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Getting my feet wet - not in Haskell though
Hi (There's still no good introduction to Monads, for example. One that's understandable for a programmer who knows his Dijkstra well but no category theory. And a few other things.) I grasped this one first time round: http://haskell.org/haskellwiki/Monads_as_containers No category theory. A basic understanding of apples and boxes is all that is required. http://haskell.org/haskellwiki/Monad has a list of about 10, plus pretty much every book/general tutorial introduces Monad's as well. If there is really nothing out there that helps you understand, you might want to prod some authors as to what isn't clear/understandable. And Haskell let's you serialise thunks just fine (use Yhc), but really if thats what you want to do, I think you are going to suffer a lot in the long run... I have written client/server app's before, the whole point is you want to decide what computation gets performed on which side, not leave it up to the vagaries of lazy evaluation to come up with a random solution. Haskell is fun, Haskell is good, but its not the right answer to every question. Just have fun doing whatever you do :) If at the end you wrote up a little summary of your project, what you used, how it went, what issues you ran into - then perhaps people can tell you (with the benefit of hindsight) how Haskell might have been. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How to serialize thunks?
Hi All those libraries really force the data because they all are written in Haskell. If you want to serialize thunks then you will need some support from RTS. Good to hear that my conjectures aren't too far from reality. Does any Haskell implementation have that kind of RTS support? Not yet. I ever don't know of anyone planning to do that. Actually I think Yhc has exactly this kind of support, and you can even ship these thunks over the wire and reconstruct them on a different machine :) http://darcs.haskell.org/yhc/src/packages/yhc-base-1.0/YHC/Runtime/API.hs Poorly documented, but it does work. Use at your own risk! Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi there are really no choices for real development. many libraries, language extensions and techniques are for ghc only I develop everything in Hugs, including the Yhc compiler itself. Hugs is great. There are lots of extensions in GHC, but Haskell 98 is a perfectly useable language! So have other compilers picked up SYB support yet? SYB and Template Haskell are just examples of techniques that make GHC obvious choice. although. SYB may be supported by Hugs too, i'm not sure GHC is the only one with inbuilt SYB support. Hugs has deriving Typeable (I think), but not Data. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi In other words, you can program in Haskell just fine without extensions. But if you want that next level in type safety, extensions is where it's at, at least for the kind of code I write. What level of safety do these type extensions give you? The biggest runtime crasher is probably pattern match failings, something that most of these type extensions don't catch at all! They do give you some safety, but not a massive amount, and not in the places where it would be truely useful. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi In other words, what on earth is good about gluing oneself to Haskell98? Life's moved on... If you stick to Haskell 98 you can: * Convert your code to Clean (Hacle) * Debug it (Hat) * Run it in your browser (ycr2js) * Document it (Haddock) * Make a cross platform binary (yhc) * Get automatic suggestions (Dr Haskell) ... Sometimes you need a type extension, but if you don't, you do get benefits. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi True, though it would be even better if the usual extensions were more widely supported, though I suppose identifying what's useful and therefore worth supporting is the point of the Haskell Prime process. Exactly the reason for Haskell Prime. As an aside I've often thought it would be better if the various components of Haskell compilers/tools would be separated out so that people could effectively build their own compiler tailored more specifically for their needs. http://neilmitchell.blogspot.com/2006/12/bhc-basic-haskell-compiler.html I thought the same thing. Note that Yhc already has a lightweight API for manipulating Yhc.Core files and one for Yhc.Bytecode files. Things are moving in that direction slowly. There is also the GHC API approach. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Versioning
Hi Jo, You seem to be describing SYB and not knowing it: http://homepages.cwi.nl/~ralf/syb1/ That basically does exactly what you've requested, in terms of traversing all items when only one matters. That said, serialisation is still a hard problem - think long and hard before picking a data format. With Yhc.Core I used Drift to derve Binary instances, keep a version tag, and if the version tags mismatch refuse to load the data. Thanks Neil On 12/20/06, Joachim Durchholz [EMAIL PROTECTED] wrote: As written in my other post, I will need to update data structures that were marshalled to disk. Now I'm wondering how to best prepare for the situation. E.g. one of the common situations is that a single data item gets replaced by a list of items. Now assume that there's a SomeData type that's used across the game, and which gets incompatibly updated SomeData1 (say, instead of containing just a string it turns into a list of strings). The update code would now have to unmarshall a blob of game data, traverse it to find all instances of SomeData, wrap them in a one-element list to turn them into SomeData1s, reconstruct the blob of game data with the SomeData1 items, and marshall the result back out to disk. This sounds as if I'd have to write code for every single data type in the update program just to update a single data type. Is that true, or is there a way around this? Regards, Jo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Getting my feet wet - small browser game
Hi Btw, if you're dumping large structures to disk, using Read/Show is a bad idea :) Just as a mention how bad it is, maybe 30 times at Show and 50 times at Read. I used to use this approach, moving away from it and learning how to use Drift was a good idea. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Versioning
Hi With Yhc.Core I used Drift to derve Binary instances, keep a version tag, and if the version tags mismatch refuse to load the data. Links? http://repetae.net/~john/computer/haskell/DrIFT/ http://darcs.haskell.org/yhc/src/libraries/general/Yhc/General/Binary.hs Thats Drift which can derive binary instances (pick GhcBinary), and then a module which can work with the derived classes. Warning, mild hacking was required to get it going on Windows. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Generics question
Hi Mark, nested type, but to do that I seem to have to create a whole other near-copy of the data declarations with slightly different names and the occasional constructor missing. I wonder if there's a better way. Instead of getting the type system to enforce it, you can write annotations that capture this restricted type. See: http://www.cl.cam.ac.uk/~nx200/research/escH-hw.ps http://www-users.cs.york.ac.uk/~ndm/projects/catch.php Note that neither of these tools are publically available, but I suspect both will be within a year or so. I'm hoping Catch will be much sooner. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project [Was: Re: What is a hacker?]
Hi Joachim, Why? In case the strictness analyzer was buggy? I'd be perfectly happy if that analysis were just a note saying run ghc with such-and-these options and inspect the intermediate code for function foo to see that the strictness analyzer determined it will always terminate. I think you are asking too much from the strictness analyzer. Why would you want strict code? Haskell's lazy semantics makes it much more amenable to equational reasoning. If you keep this laziness you can do all manner of proofs on the code. If what you want is real-time guarantees then something like the Hume project might be what you are after. Shoving a strictness analyser over a piece of code only returns info about the WHNF, nothing deeper. If you take it as anything more than an optimisation hint, it will come back and bite you... If what you do want is termination proofs, then you want this: http://www-i2.informatik.rwth-aachen.de/giesl/papers/RTA06-distribute.ps Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project
Hi Obviously when Cost(Upgrade) Cost(Optimisation) for the customer. Those costs are Cost(Upgrade) = Price of more memory or new PC which is fast enough. Cost(Optimisation) = Hours_spent * Fee_per_Hour / N You are talking closed source commercial software for the masses. I don't know anyone who distributes software like this written in Haskell (although I'm sure there might be one or two) Now imagine working for a single company, or for small volume software. You ask them to upgrade, they turn around and say bye bye. Now imagine you are working for a company, and have to convince people to throw away C and move to Haskell. Haskell is too slow will often be an initial argument, if its in any way right, that will be enough. Now imagine you are writing an open source project. People will turn around and use a Haskell compiler written in C (Hugs) instead of one written in Haskell (GHC) because its 100 times faster to load the program. Imagine you are writing a version control client, people will complain because certain operations take 100's of years on their big Haskell repo. [I use Hugs, and complain that darcs on the Yhc repo sometimes goes into virtual non-termination - although I love both GHC and darcs at the same time] Speed is sometimes important. Let's not forget that and wheel out cost of hardware arguments. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re : [Haskell-cafe] Re: A suggestion for the next high profile Haskell project [Was: Re: What is a hacker?]
Hi minh thu, Lazy semantics - equational reasoning ? I thought that : lack of mutable state - equational reasoning. For instance, I think to data flow variable in Oz (whcih I really don't know much / never used) : if a (Oz managed) thread attemps to read the value of an unbound (data flow) variable, it waits until another thread binds it. But the equational reasoning (referential transparency) remains (and the evaluation is eager by default). Lack of mutable state, referentially transparent and laziness all help with equational reasoning. Inlining is much easier in a lazy language - and inlining is really handy for equational reasoning. Imagine: not_term = non_term f x = 12 Now evaluating: main = f non_term In a lazy language the value is always 12, in a strict language its always _|_. Now let's inline f: main = 12 In a lazy language the value is still 12, in a strict language the value has changed. Note how in a strict language inlining is not as safe as it once was... Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A suggestion for the next high profile Haskell project
Hi I don't know if any actual language does this, What, that is strict and would like to inline things for performance? There is a reason they can't do this. but your inlining problem can be solved by letting _|_ = arbitrary behaivor. So would you allow folding? (inlining = unfolding) i.e. replacing defined behaviour with _|_? And how many equational reasoning steps do you have to go, before your program is totally different? Equational reasoning is easier in a lazy language. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Showing the 1 element tuple
Hi, A weird question, what does the 1 element tuple look like? () -- 0 element tuple (,) a b -- 2 element tuple (,,) a b c -- 3 element tuple () a - meaningless (a) - a in brackets GHC has the 1 element unboxed tuple, (# a #), and all the other sizes unboxed as well, but how would you visually represent the 1 element boxed tuple? As it happens, Yhc _does_ have the 1 element tuple, you just can't use it from normal programs, its only created by desugarings of class instances. I'd quite like to change this, and I also need to render the 1 element tuple in some way, so wondered if anyone had any good ideas (or if there is even some sort of convention) I currently use ()1, but don't like that as it doesn't follow Haskell rules - the () and 1 would be separate lexemes. My other thought is (?), where ? is something appropriate - but all the appropriate things I can think of would either not be a lexeme (i.e. 1), having an existing meaning (i.e. . | etc) or seem wrong. Thoughts? Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Showing the 1 element tuple
Hi Python uses the syntax (foo,) to denote a singleton tuple (that is an extra comma at the end); quoting the python tutorial Ugly, but effective. Yes, I thought of that, the issue is: (a,b) is considered syntactic sugar for (,) a b (a,) is syntactic sugar for... And the place I'm displaying this is definately after desugaring! Could tuples be implemented as an HList? singleton = (`hCons` hNil) Not in Yhc, no higher rank types :) Also tuples are really really common, every class function has quite a few floating around - HList is just too much overhead (I think). Tuples represent dimensionality therefore a 1-element tuple is just a 1-dimensional value ie the value itself hence a == (a) == ((a)) == (((a))) Tuples are a box you can put things in, in Haskell: data Tuple a = Tuple a Tuple (Tuple 1) /= 1 (either at runtime, at type time, or any other time) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project
Hi Bulat, let's go further in this long-term discussion. i've read Shootout problems and concluded that there are only 2 tasks which speed is dependent on code-generation abilities of compiler, all other tasks are dependent on speed of used libraries. just for example - in one test TCL was fastest language. why? because this test contained almost nothing but 1000 calls to the regex engine with very large strings and TCL regex engine was fastest It's more than 2 tasks that are dependant on the code generated by the compiler. And in my opinion, generally the Clean solution was the nicest in terms of speed/performance. There is absolutely no reason Haskell can't be as fast as Clean. Clean doesn't seem to go to the imperative style in most of the benchmarks. I think Bulat has a point, currently the speed of idiomatic Haskell lags behind that of idiomatic C. But the two responses to that have to be currently, but not forever. And idiomatic C is like pulling out your own teeth with a pair of pliers - sometimes necessary, but never fun. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A suggestion for the next high profile Haskell project
Hi, Is that an intrinsic feature of the language, or could compilers' optimisation plausibly get clever enough to do well without lots of seq and explicit unboxings and suchlike? I believe that compilers can get a lot cleverer - my hope is that one day the natural Haskell definition will outperform a C definition. Of course, lazy evaluation makes that hard work, but I think it can be done eventually. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I'd like start with Haskell, but...
Hi Waldemar, The final aim of the aproach is to get a tool in which there will be no syntactic errors during modelling bussiness logic. Recently I've finished very primary version of the tool (0.001:-). Ah, now that sounds like Haskell might be good for :) Haskell isn't great at writing a GUI and database combination, in my experience. It certainly can, it just tends to be a bit of work. Having said that, Haskell is _great_ for writing domain specific libraries, for plugging together new applications and for modelling business logic. It's likely that your business logic has some standard set of operations, which you combine in some way - this is the thing Haskell excels at - defining small things, and combining them in new ways. The type system will help to ensure that the combinations are good, which again helps reduce errors. I do not know C#, but what was attracting me to Haskell is - as they say - compact, clean and very functional way of programming. Yes, a well designed Haskell program will give much better separation of concerns. You can totally separate the logic from the user interface gunk, and it will be more maintainable. Maybe, but what is still unclear for me: Haskell is wrong for GUI/Database application because of lack of good libraries or because of it's way of programming??? The libraries for GUI programming are not great - they are progressing, and can certainly be used to develop tools, but I don't feel they are the good stuff yet. Maybe I'm just setting the bar higher because the rest of Haskell is so nice. The current style of GUI programming in Haskell tends to be in the IO monad, and feel very much like imperative programming. Haskell is perfectly capable of being an imperative programming language where required, but its not as natural as something like C# in this respect. So in answer to your question, I'd say a little of both, but with the optimistic view that one day someone will figure out what a GUI program in Haskell should look like and everyone wlil be happy :) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building the community
Hi * Give tips on how to answer questions + Ok. we can put up an article here. Some suggestions: - No questions are bad questions - Code should come with examples of how to run it - Solutions with unsafePerformIO should be discouraged (moreso ;) - Be polite! (we're good at this) I'd say our worst feature is tending to give solutions which are not simple Haskell, but make use of advanced features. When a beginner asks a question, sometimes the answer requires GADT's, Template Haskell, rank-2 types etc. However this is usually because they asked the wrong question - thinking in an imperative frame of mind. Often it would be better to peel back to the original problem, where the answer is more likely to be pure neat Haskell. I guess unsafePerformIO is just one instance of this. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] interpreter ouput in color
Hi Walter, Hi all. I was wondering if some people miss the colored output of some applications, such like the IPython enhanced shell. I've been googling for similar options for Haskell but I found nothing. WinHugs already colours (to some degree) and hyperlinks error messages. http://www-users.cs.york.ac.uk/~ndm/projects/winhugs.php (screenshot on that page) GuiHaskell does it a lot more, with full syntax colouring of error messages and hyperlinks. Unfortunately it can't be used reliably at the moment due to threading issues with Gtk+Gtk2Hs+GHC+Windows. http://www-users.cs.york.ac.uk/~ndm/projects/guihaskell.php GuiHaskell merely wraps GHCi (and Hugs and other stuff), so allows syntax colouring to be implemented without diving into the GHC source code. Thanks Neil PS. The Haskell-cafe mailing list is better for this sort of question, haskell tends to be more used for announcements, so i've sent the follow up there. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Stack, Heap and GHC
Hi Did you compile with -O (optimisations). Sometimes this fixes things, and its just good practice. It's slower to compile, and might fix things in GHC Haskell, but other compilers don't all have -O flags, so its generally best to make your program at least have the right sort of time/space behaviour using Haskell. If your code doesn't work without -O, then it probably won't work in Hugs or Yhc. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell and .NET
Hi Yhc also has a .NET generating capability, just pass the -dotnet flag. http://haskell.org/haskellwiki/Yhc Thanks Neil On 12/12/06, Monique Monteiro [EMAIL PROTECTED] wrote: Hi Justin, I've runned a research project about this topic (in fact, it was the subject of my MSc dissertation). Please see the Haskell.NET Project (http://www.cin.ufpe.br/~haskell/haskelldotnet). We have compiled a subset of the Haskell language to .NET, but we still don't have an available release (we don't support the full Haskell prelude yet). The compiler is an extension to GHC. In the future, we intend to provide full interoperability with .NET in this way. There are some interesting references in the website about our compilation strategies. If you need further information about the project's status, please contact Prof. André Santos ([EMAIL PROTECTED]) and/or Guilherme Avelino ([EMAIL PROTECTED]). Best regards, -- _ Monique Monteiro, MSc http://www.cin.ufpe.br/~mlbm http://thespoke.net/blogs/moniquelouise/default.aspx [EMAIL PROTECTED] +55 81 34198137 Project Manager Recife Microsoft Innovation Center ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Micro-contributions to MissingH
Hi I'm wondering if I should submit this as a patch for MissingH. If so, where in the new hierarchy should this be placed? I submitted 3 patches to missingh about a week ago, but have heard nothing back since. Did they get spam filtered or something? Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell and .NET
Hi Krasimir, to produce code with reasonable performance. The major problem with YHC is that it still doesn't have strictness analyzer. It does, or rather Yhc.Core does (see Yhc.Core.Strictness - http://www.cs.york.ac.uk/fp/yhc/snapshot/docs/Yhc-Core-Strictness.html). This was only done a few weeks ago, so the .NET translator has no benefit from it. And strictness is not the biggest problem, a complete lack of any optimisations is, but I'm working on that one too! Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell and .NET
Hi And strictness is not the biggest problem, a complete lack of any optimisations is, but I'm working on that one too! It is great to hear that. Of course an optimiser will be beneficial too but I guess that even the benefit that the code generator can have from the strictness analyzer will make huge difference. In the GHC back end I seem to remember strictness gives a 10% performance improvement, but let motion gives a 30% improvement - its quite likely that .NET will benefit more from strictness, but still the general optimisation is probably going to be a bigger win. I think basic strictness information gained about 5% in the Javascript Yhc backend, so not great amounts. The optimiser does generalised deforestation, and loads of other cool tricks, so I'm hoping for at least 50% over the normal Yhc code :) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Request for a Simple Pretty Printing library
Hi, I've been using the HughesPJ pretty printing library, but I need a new combinator: wrap :: String - Doc - String - Doc wrap prepend doc append = ... The semantics of this would be that the text is prepended and appended to the doc when rendered, but does not alter the pretty printing at all. The idea of this is to support printing with HTML rendering: wrap span class='keyword' (text case) /span The HughesPJ library is 1000 lines long, so will be quite a lot of work to change this to get it working properly. Is there a simpler pretty printing library, with source code available somewhere? Ideally using the same interface. Of course, if anyone knows how to make this combinator using the existing library, or using another existing library, I'd appreciate it. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Request for a Simple Pretty Printing library
Hi Something like: wrap prepend doc append = zeroText prepend doc zeroText append zeroText s = textBeside_ (Str s) 0 Empty Thanks, that works great! Is there likely to be any support for adding this to the standard library? I'd rather not have to fork a version of HughesPJ to get this feature. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Aim Of Haskell
Hi That's exactly the problem! For most people there *is* no difference. You say functional programming to most people, even professional programmers, and usually the only chance you have of getting them to understand what what you mean is by asking so, have you heard of Lisp, or Scheme? Talking to professional programmers, if I tell anyone I program in Haskell they nearly always say oh, Pascal, that's cool. No one knows what functional programming is, Scheme/Lisp are the closest. Maybe we should try and hijack the phrase functional programming - Haskell is just too similar to Pascal. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Pretty printing HTML
Hi, I want to pretty print some text as HTML, using the standard HughesPJ combinators. The problem is that I want the length of a text string to be its textual context, not its character length. For example, a keyword will display as case, but internally will be the string span class='keyword'case/span Is there any way to acheive this? I have come up with something, but its not nice at all. It basically involves parsing the generated text and inserting the extra HTML back in. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Refactoring recklessly
Hi I'd like to be able to reorganize my code and then verify that I didn't change any functionality. That is, the old and new code have precisely the same meaning. Also, I'd like to be able to change a function and verify that efficiency was the only thing affected. Are either of these possible in Haskell or any language? They are possible in any language, just in some they might have a lot of work to do the proofs. In Haskell they are pretty easy: http://haskell.org/haskellwiki/Haskell_Equational_Reasoning_Assistant (More one function at a time, not publically available, as far as I can tell) http://www.cs.kent.ac.uk/projects/refactor-fp/hare.html (Global refactorings, a nice tool) Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] One question...
Hi Waldmar, Now my problem is connected with the non-update object feature. I can't write variable instead object because - from the meaning of the word ( variable ) - it has the possibility to CHANGE its value. Yes that my problem :-( main = do username - read_info_from_user do_whatever_is_needed print username Try not to think of this too hard. Once you start learning Haskell you'll suddenly realise a lot of the problems just don't happen if you think the Haskell way. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Download locations for former-base libraries?
Hi Of course, just saying download the latest version with darcs isn't useful, either. People that want to use my package shouldn't have to have darcs, and they also shouldn't have to fight with broken development software. Or should I be telling people to download the GHC 6.6 extralibs source? That doesn't seem quite right either; it's packaged as a tar.bz2, but what would a Windows user with HUGS do? That person probably couldn't even unpack it. I started doing some work towards this on windows: http://www-users.cs.york.ac.uk/~ndm/projects/windows.php I found that generally working out of the darcs repo's is both horribly unreliable, but the easiest way to go about it, because its more consistent. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GADT vs Arrows for parsers/FSMs/etc.
Hi It seems like Haskell has two emerging idioms for parsing and fsms: GADTs and Arrows. What about something else? If you limit yourself to the two things that look new and cool (where emerging is another word for new, and idiom seems to be the current Haskell word for cool), you miss out on all the tried and tested stuff. I am thinking about using one of these idioms to represent server structure in a future version of HAppS but I'm not sure where to start. Why would one choose one or the other? I would pick Arrows (over GADTs) because Arrows are Haskell, and are supported by multiple Haskell compilers. Other than that (as far as I was aware) these two things are massively different, so I wouldn't have thought it was a one or the other choice usually. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] 2D Array
Hi unsuitable. It seems that a Map Int (Map Int a) is the most suitable structure, but this seems cumbersome. You might want to use IntMap, which is a version of Map specialised to Int's, with better time bounds. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell source transformer?
Hi Dimitry, I know there is a Haskell syntax parser around (maybe, more than one). Does anybody know of any utility based on such parser that does things I need, or rather a library on top of the parser? I just would like to avoid reinventing the wheel. I have a Haskell parser here: http://www.cs.york.ac.uk/fp/darcs/catch/src/Haskell/ - originally from GHC but modified slightly by the Hacle project to work in Hugs and be Haskell 98 (I think). I am also intending to write a Yhc.Parser library, but haven't got round to that yet. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] New Name for MissingH?
Hi The alternative I've been thinking of is something like Haskell Utility Library (HUL). Yuk. I like MissingH. MissingH suggests things that are missing from the standard set and provided here. HsMissing would be my preferred choice, but its not really important. Haskell says which language its written in, library says its a library, and utility tells me nothing (the word is too overloaded). By the end I know its a Haskell library... I think the problem isn't that the name is confusing, but that no one knows it exists or what it does. Things like adding it to the Hoogle database would probably help, along with greater there is a function for that in MissingH posts to the haskell-cafe list as people ask. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: New Name for MissingH?
Hi I couldn't figure out how to add it to hoogle. Does anyone have a pointer for that? Wait for Hoogle 4, and bug me. Hoogle 4 will allow additional libraries to be searched. Once its ready I'll add MissingH. database would probably help, along with greater there is a function for that in MissingH posts to the haskell-cafe list as people ask. True, too. I didn't want to be too annoying, so I have tried to not do that too much. But since you asked, I'll try to step in more. I think its a great way to both promote MissingH, and help newcomers at the same time. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building Binaries with Cabal
Hi
let mydescrip = case System.Info.os of
mingw32 - descrip
_ - descrip {buildDepends =
Aghhh! To test if the operating system is windows you
compare against a hard coded string which _isn't_ an OS, but _is_ an
optional component by a 3rd party. It's required to build some Haskell
compilers, but for Yhc and Hugs its not required at any stage, and its
presence is optional!
I know this isn't your fault, it just scares me deeply that os could
return something that isn't an os! How about we add a cpu string,
which returns the amount of RAM installed. Or how about we add a
compiler string, which returns the users surname...
Thanks
Neil
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Re: [Haskell-cafe] Building Binaries with Cabal
Hi Your point is well-taken, but the distinction is useful. If running on cygwin, my platform is essentially POSIX, even though the OS is Windows. Yes, but _my_ OS is reported as mingw32, even though its never been installed on this computer... Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generating javascript
Hi Jeff, It all depends how you want to write your code. The two options are full Haskell (Yhc) or combinators (HSPClientSide). Thanks Neil On 11/29/06, jeff p [EMAIL PROTECTED] wrote: Hello, There's a Google SoC-project made by a friend of mine for JavaScript support in Haskell Server Pages: http://csmisc14.cs.chalmers.se/~bjornson/soc/ It's a combinator library, but i'm not sure it's what you really need though. :) This seems to contain just what I was looking for. Although I'm not using HSP, it looks like the HSPClientside library can be used (in conjunction with Text.XHtml) to generate webpages with embedded scripts. thanks, Jeff ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] generating javascript
Hi Anyway I encourage you to have a look at HSP as well :-) It's quite nice to be able to use regular XML syntax within the Haskell code. I think it should be entirely possible to use Haskell with Yhc and HSX (http://www.cs.chalmers.se/~d00nibro/haskell-src-exts/), so you can still write proper XML for your client side HTML. This is the way Hoogle 4 is going to be written. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Future of MissingH
Hi John, Should this all be one library? No, several smaller libraries would be nice. Should the module naming scheme be changed? Yes, MissingH is not the place to put these things. You run the risk of more name clashes, but thats ok. Could, and should, any of this be integrated into the Haskell libraries project? Yes, some should, but only after careful review and being split up. Assuming the Haskell libraries project is still something that should be continued, once Hackage is up and running suddenly the distinction becomes minimal. A few of the functions should be picked out and moved into base, where they truely are missing. How could greater community participation be encouraged, while still encouraging quality control? Make sure more people know about it. I want to start using MissingH but never got around to it, by continually telling me how great it was I'm sure I would have started using it earlier. I have various bits of general libraries strewn around the place, which I might contribute to MissingH. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] The Future of MissingH
Hi How could greater community participation be encouraged, while still encouraging quality control? It also took me quite a while to find the darcs repository, and as far as I can see there is no web page on what MissingH has in it, other than a textual readme and the GNU entry. If there was a single web page which said what MissingH was and where it could be found, that would help people. The darcs repo I found was: http://darcs.complete.org/missingh/ Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Arrows tutorial
Hi Small arrows tutorial (sorta, I'm learning myself and trying to doc as I go): http://www.thenewsh.com/~newsham/x/arrow.txt Why not shove it on the wiki? Then everyone can find it, improve it, and treasure it forever more. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wiki page for rewrite rules tips, types and tricks
Hi Great page, I especially like the phrase: [...] changing a non-terminating program [...] into a much faster one [...] And one important point: In general its a bad idea for rules to change the semantics (meaning) of your code in such a way. Consider someone using reverse . reverse to demand strictness of an IO action (I've seen this in conjunction with interact), this code would no longer work with the above rule. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] importing Distribution.Compat.FilePath fails
Hi How about using this instead: http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php#filepath The only reason would be that it isn't in my GHC install by default (I'm on Debian Sid). However, I suppose I can look at this as an excellent first experiment with Cabal and packaging Haskell libs for Debian :-) Thanks for pointing it out. Looks like a perfect fit for me! I think someone is packaging this for Debian already, you might want to email the debian haskell list to check and avoid duplicated work. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Debugging partial functions by the rules
Hi
How controversial would a proposal to {-# DEPRECATE fromJust #-} be, in
favour of:
Just _ = x -- which will give you the precise line number
It seems to me this is one cause of mysterious newbie errors we
could easily discourage, with little harm.
Btw, I'm not seriously suggesting removing it ;)
It could be discouraged ever so slightly in the haddocks though.
I strongly disagree. If we are removing things that confuse newbies
why not start with higher rank types, MPTC's and GADT's ;)
fromJust is simple, useful and clear. What you mean is that
implementations aren't very good at debugging this. It seems unfair to
blame partial functions for the lack of a debugger. If a call stack
was automatically output every time a fromJust failed would this even
be something people complained about?
Thanks
Neil
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Re: [Haskell-cafe] Debugging partial functions by the rules
Hi I have always been wondering why error shouldn't always return a call stack from the occurrance of fromJust up to the function I typed into ghci (or up to main, for that matter). yhi-stack (as yet unreleased) does exactly this, without requiring you to recompile your code even. hat-stack also does this. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Debugging partial functions by the rules
Hi Yes, these techniques are fairly well known now, and hopefully some of the more experienced Haskellers are using them (I certainly use the non-empty list tricks). Any anyone with more than 6 months Haskell knows to avoid fromJust. I'm not, I use fromJust all the time. Ditto for head, init, maximum, foldr1... One solution would be to deprecate fromJust (we recently decided not to add fromLeft/Right for the same reasons). Having a compiler warning is a good way to encourage good behaviour :) We didn't decide not to add fromLeft/fromRight, Russell decided to defer it to a later patch. I am still very interested in them being put in! There seem to be two sides forming to this issue - use partial functions or don't. I don't see why we should restrict the functions available to the partial people, when the unpartial people can choose not to use them. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Debugging partial functions by the rules
Hi Should Haskell also provide unrestricted side effects, setjmp/ longjmp, missile launching functions, etc? After all, people who don't want to use them can just avoid them. :) Fair point. But if you eliminate incomplete cases, and the error function, you'd probably need to increase the power of the type checker by introducing dependant types. It's a good research avenue, and an interesting approach, but its not what Haskell is to me (but it might be to others). Every time I read code containing these functions, I have to perform a non-local analysis to verify the invariant, or even to determine the invariant. If you use the Programmatica annotations, the ESC/Haskell annotations or Catch then you can have these assertions checked for you, and in the case of Catch even infered for you. Admitedly ESC/Haskell and Catch aren't ready for use yet, but they will be soon! Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
