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Some FC++ comments
by Vladimir Prus 09 Apr '04

09 Apr '04

I've just made a first attempt to read through FC++ docs, and have some comments. I haven't read all of the posts in the recent review, so apologies if some of the issues are already known. The docs I used are those at http://www.cc.gatech.edu/~yannis/fc++/boostpaper/fcpp.html First, a motivating example: I wanted to find a vertex in BGL graph which has in degree of zero. This should be something as simple as (using lambda): find(vertices(g).first, vertices(g).end(), bind(in_degree, _1, g) == 0); but in_degree happens to have several overloads, all of which are templates, so just 'in_degree' won't work, and selecting the right variant via cast has it's own problems. So, I though FC++ would allow me to declare 'in_degree_f' object that will work for all kinds of graph. The documentation starts with: FC++ is a library for doing functional programming in C++. The library provides a general framework to support various functional programming aspects, such as higher-order[1] polymorphic[2] functions, The issues with this are: 1. When this is in context of proposed Boost.FC++ docs, one immediately wonders how this is different from Boost.Lambda. 2. The footnotes always break the regular flow of reading, so it's better not use them in the first sentence new user is likely to see. 3. higher-order polymorphic functions exists even without FC++. I think boost::bind is such a function: it takes function as argument and returns a function. So, this statement does not indicate what new FC++ brings (btw, I agree it brings something new). 4. If you think that average reader will think that 'polymorphic' == 'with virtual functions' you might want to use the word 'generic'. Later, you define 'functiod' and the definition applies just nice to functional objects everybody was using for quite some time. Again, you don't explain what FC++ brings. Later, you describe changes made during boostification. I really don't think new user would be interested in that. The above comments might sound like nit-picking, but what I try to say is: the instroduction does not say absolutely anything about why FC++ is worth looking at. The only new term there is 'lazy_list' and if reader doesn't know what's that already, he might not get even that. In section 2, you say: Programming in this pure style ensures referential transparency. and I don't know what "transparency" here means. Now, to section 4, "Overview". What I'd expect in this section is a bunch of examples, showing what I can do with FC++ which is not easily done using other tools. What I see, though, is: We could define a polymorphic functoid add_self(), which adds an argument to itself: // add_self( x ) means x + x If we can define such thing, I'd really like to see the definition, not commented out code. The you talk about lazy list, again for someone who has no idea what they are, it's hard to understand usefullness. I think you should either explain this with an example, or at worst give some link. E.g. "Why functional programming matters" makes some use of lazy lists, IIRC. The overview does on in largely the same style. You list supported functoids but don't give any explanations or example. Last comment on this section: plus(3,4) // 3+4 also minus, multiplies, etc. This does not look impressive. Can't I do "std::plus<int>(3,4)". I think one of the points of FC++ is that you don't need to specify the exact type. If so, you need to explicitly state that fact (and preferrable, even in the introduction). Now to the Section 5. Direct functoids enable the creation of functions Hmm.. is it precisely "enable". I suspect that "direct functoid" *is* the function. Or is direct functoid is some device which produces functions? I think the example with 'map' is not really good. First you say map takes a list and function. Then you give Haskell syntax and describe that syntax. After that you explain what's high-order and what's polymorhic. IMO, the Haskell syntax is just not necessary here. Later you say: Representing such a function in C++ is non-trivial Then, what about std::transform? If we forget that it works on iterators, not sequences (which is just detail) then it does exactly what you're after. I think it would be better if you write down properties of the function you want to create (polymorphic, can be passed as argument *itself*, allows to inter return type) and then immediately give an example. And example could be more reabably you use split the definition of 'result_type' like this: template <class F, class L> struct sig { typedef F::template sig<typename L::value_type>::result_type function_return typedef list< function_return > result_type; }; It might be better to use 'type' instead of 'result_type' since MPL uses 'type'. When you talk about monomorphic direct functoids, I wonder why you need 'c_fun_type'. Is it possible to make std::unary_function work? The section 6, "Indirect Functoids", makes me wonder if they are usefull at all. boost::function works very nice with me, and it also works with boost:bind. The secton 7, "Full Functoids" looks ok to me, though some examples would be good. At this point I've stopped reading documentatation, tried to write some code and got my 'in_degree_f' in a short time. There are some additional questions: 1. Maybe it makes sense to provide a helper base class for a case where return type is fixed, but argument types are not. Something like: class xxx_in_degree : public ret_type2<unsigned> { ... } ; 2. Do we need intermediate typedef? Won't boost::fcpp::full2<xxx_in_degree> in_degree_f; work just fine? 3. I have std::find_if(vertices(g).first, vertices(g).second, in_degree_f(_, g)); but I want to compare the return from 'in_degree_f' with zero, as in thes example: find(vertices(g).first, vertices(g).end(), bind(in_degree, _1, g) == 0); How do I do that? When I try: std::find_if(vertices(g).first, vertices(g).second, lambda(X)[ in_degree_f[X, g] %equal% 0]); I get a lots of errors, starting with: fcpp/signature.hpp:114: error: invalid use of undefined type `struct boost::fcpp::impl::XEqual::sig<size_t, int>' The complete example is at http://zigzag.cs.msu.su:7813/bgl.cpp if needed. Also, it would be *really* nice if lambda syntax in FC++ and Boost.Lambda was compatible. I'll print and read your paper on syntax today, but no matter how big semantic differences are, learning/using two different syntaxes is a bad idea. These are all comments for now. Hope they make sense. - Volodya

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Lambda regression with GCC-3.4
by Michael Stevens 09 Apr '04

09 Apr '04

Hi All, (particularly Jaakko!) While working on using BLL's operator return type mechanism in uBLAS I stumbled on the problem the recent (snapshot) GCC-3.4 has with BLL. I noticed Jaakoo checked in the following patch a few days ago as a workaround. #if BOOST_WORKAROUND(__GNUC__, == 3) && __GNUC_MINOR__ >=4 #include <vector> #else namespace std { template <class T, class Allocator> class vector; } #endif >From my own research the problem is not just restricted to 'std::vector'. It certainly also occurs with 'std::map'. I assume (have not verified) that the problem is related to hidden template parameters in the gcc-3.4 implementations of the std containers. OR is the problem simply a bug (an regression) in gcc 3.4 Too late for gcc 3.4 but I will submit a bug report if no one else has already done so. Michael -- ___________________________________ Michael Stevens Systems Engineering Navigation Systems, Estimation and Bayesian Filtering http://www.sf.net/Bayes++ ___________________________________

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Re: [boost] Formal Review: Assignment Library
by Vladimir Prus 09 Apr '04

09 Apr '04

Tom Brinkman wrote: > The review of Assignment Library library, written by > Thorsten Ottosen 2003 (nesotto(a)cs.auc.dk) starts > today(April 1, 2004)and runs for 10 days. I think the library should be accepted, though I have some suggestions. The review below is based on reading the documentation for about an hour. First off, I think such a library is usefull. Besides stl container initialization, it would be usefull for other libraries which want to provide convenient initialization syntax. Now, to the suggestions 1. The library expects the user to overload 'make_insertion' for his types. Now suppose I have 'class Email' which list of 'to' and 'cc' addresses.I want to initialize both using the assign library, e.g Email e; e.add_to("Winnie-the-Pooh")("Ia"); e.add_cc("Story writer"); The problem is that I can have only one 'make_insertion' for the 'Email' class. Exposing the real containers used for storing addresses is not good idea. And there might be 'add_to_address' function which does additional handling of argument, before pushing it into the container. So, it would be nice if the library allowed to specify a *function* which will do the actual insertion. 2. The library examples contain using namespace assignment; which is likely to burn users in a subtle way. Suppose: // some header namespace email { class Email {}; std::ostream& operator<<(std::ostream& os, const Email& e); } // some source #include "some header" namespace email { using namespace assignment; void internal_function() { vector<int> v; .... v << 1, 2, 3; } } The operator<< declared in the namespace will hide the one from "using namespace", and unless user is aware about this problem he might spend a lot of time trying to understand why the right operator<< is not selected. I know it costed me about 1 hour some time ago. 3. While the += operator is fine with me, I don't like the << operator. I cannot associate the conventional meaning of the operator with 'assign all' semantic, so I suggest that this operator is dropped completely. You can provide alternative syntax for assign_all: assign(v) = 1, 2, 3, 4, 5; if assignl(v)(1)(2)(3)(4)(5) has too many paranthethis. (Since comma has lower predecence than =, the first syntax will really work). 4. The operator() and other operators in insert_assigner are declared inline. Suppose vector<some_type> v; assign(v)("first", "")("second", ""); This involves call to constructor of 'some_type' and possible calls to additional constructors needed to converted char* into types that 'some_type' excepts. If operator() is inline, those calls will be inlined as well, increasing code size. Similiar problem exists because single-argument operator() accepts a fixed type, possible requiring convertion on the caller's side. I'd suggest the declare the operators outside of class declaration. This will give the compiler more freedom -- e.g. inlining only if maximum optimization level is requested. 4. Just like other revievers, I'm not comfortable with monolitic stl.hpp 5. Operator += which is declared for all possible types makes me nervous. IIRC, stl formatiing library by Terje Sletteb used some trick to avoid exposing all those operators. Something like template<template<class T, class Alloc> sequence> class helper { friend std::ostream& operator<<(std::ostream&, const Sequence& s) { ... } } // in vector.hpp template helper<std::vector>; Terje said the explicit instantination bring the friend declaration into namespace. I'm somewhat rusty on friend lookup rules, so further investigation is needed. Documentation issues 1. The example for maps uses: map<const char*, int> month; which is a bit strange, even for example, given that comparison for "const char*" does not compare string values 2. In the graph example, I'm not sure how you add edge between vertices 4 and 6, in a graph with only 5 vertices. If new vertices are automatically added, this should be documented. And BTW, what about graph which don't use ints for vertex_descriptor? 3. I did not really understoon 'tuple_insert_assigner' role. Why is it needed? - Volodya

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RE: [boost] Re: FC++ -- Formal Review Result
by Jon Kalb 09 Apr '04

09 Apr '04

I would like to thank Brian, Mat, and all of the FC++ library reviewers for their work on this submission. It is clear that C++ has some form of functional programming in its future and I'm glad we have people of this caliber working on it. Whatever we end up with in Boost and eventually in the Standard, whether it is a future submission of FC++ or some other approach, it will be better for the work that Brian has done in this version and I think we are indebted to him, Mat, and the library reviewers for their effort. Thank you. -- Jon Kalb

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A new GUI library
by Mohammed Iqbal 09 Apr '04

09 Apr '04

Hi... I have written a GUI for WIndows XP only (this library will not work on Win 2000 and/or 98) in C++. Of course this library doesn't conform to the guidelines to post it here. This library works only with gcc 3.3.3 and Visual C++ 7.1 only. It is based on ideas inspired by the work of Alexandrescu "Modern C++ Design" and Czarnecki and Eisenecker "Generatie Programming" and by following a new technique called Context-Oriented Programming. Boost has a nice small libraries that I rewrote to fullfil my needs. This library is not complete yet because it will cover every thing for WinXP only. Of course, this means it can't be posted to this discussion list nor the CVS. Mohammed

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[BGL] Tarjan's offline LCA algorithm.
by Cromwell Enage 09 Apr '04

09 Apr '04

I know this was a couple of days overdue, but I'm still learning my way through CVS. If there's still an urgent need for the LCA algorithm, here it is: <http://groups.yahoo.com/group/boost/files/bgl_algo/tarjan_offline_lca.zip> The example program provides a straightforward way of using it. Known issues: * The graph needs to be directed or bidirectional, it must be a tree, and the user must provide the root. * I forgot to discuss what type of output was desired. As a "quick and dirty" approach I used a Boost.uBLAS matrix; if you have any ideas that could lead to better efficiency and genericity, please let me know. The documentation covers my approach in greater detail. * The disjoint sets parameter is available in the kitchen-sink version of the function but not in the default version; the object is strictly for utility purposes. The bgl_named_params class doesn't appear to provide the ability to include custom named parameters; for this reason, I haven't included a named-parameter variant. If you disagree, please let me know. * I tried implementing Tarjan's LCA using the builtin depth-first-search function and event visitor lists. The major stumbling block was my inability to execute any code during post-traversal of an edge. (The on_tree_edge event fires during pre-traversal, and neither the on_back_edge event nor the on_forward_or_cross_edge event would fire using DFS on the example graph.) So, in the future, I'd like to see an on_post_traversal event filter and a corresponding vis.post_traversal(edge,graph) function implemented, and I'm pretty sure other graph algorithms could use this feature, too. For the moment, the LCA algorithm runs its own recursive DFS, and the event visitor list parameter in the kitchen-sink function variant does nothing. BTW, one of the Java source files (the one with the Graph class) was missing, so it was necessary to restart from scratch. HTH Cromwell Enage __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/

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Regex ease-of-use ideas
by David Abrahams 09 Apr '04

09 Apr '04

I was just writing up a simple tutorial example; finding the subject in a set of email headers. Here's what I got: std::string line; boost::regex pat("^Subject: (Re: )?(.*)"); boost::smatch matches; while (std::cin) { std::getline(std::cin, line); if (boost::regex_match(line,matches, pat)) std::cout << matches[2]; } 1. There's no way to search a stream for a match because a regex requires bidirectional iterators, so I have to do this totally frustrating line-by-line search. I think Spirit has some kind of iterator that turns an input iterator into something forward by holding a cache of the data starting with the earliest copy of the original iterator. Could something like that be added? 2. Seems to me that if match objects could be converted to bool, we might be able to: std::string line; boost::regex pat("^Subject: (Re: )?(.*)"); while (std::cin) { std::getline(std::cin, line); if (boost::smatch m = boost::regex_match(line, pat)) std::cout << m[2]; } which would be much smoother to the touch. Are match objects expensive to construct? -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[boost-sandbox] [BGL] Random path and Tarjan's Offline LCA algorithms.
by Cromwell Enage 08 Apr '04

08 Apr '04

They're now in the Boost Sandbox CVS, hooray! Accordingly, I've deleted the corresponding archives from the Yahoogroups file vault. The loop_erased_random_paths function has been changed to take in a boost::random_number_generator (or equivalent class) rather than a random number generating engine. Unfortunately, the following bug prevents the example and test programs from working correctly: <http://sourceforge.net/tracker/index.php?func=detail&aid=911758&group_id=75…> In the meantime, I'll be studying an all-pairs LCA algorithm that I've recently stumbled upon for which matrix output may be better suited. Cromwell Enage __________________________________ Do you Yahoo!? Yahoo! Small Business $15K Web Design Giveaway http://promotions.yahoo.com/design_giveaway/

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RE: [boost] Re: FC++ -- Formal Review Result
by Powell, Gary 08 Apr '04

08 Apr '04

>> Do you think there would be merit in starting over from scratch? >> With a new language, I mean. >Of course. But adoption and interoperability are difficult issues, >then. http://felix.sf.net has one interesting strategy. This is of course a similar approach that C++ did to usurp "C". Generate code in a language that the machine is likely to have a compiler for. Without doing this, the chances of a new language being adopted by businesses which have bizillions of euros invested an existing code base and trained engineers is nil, nada, squat. By doing this a small test project can be done on the side by a team and if the results are good, integrated into the rest of the company. (If poor those left on the project when its cancelled will be terminated and forced to look for employment under assumed names.) The key is having both a "compiler" and a "debugger" that understands both languages at the source level. The quotes are to indicate that an interpreted language is not ruled out. Anyone who tried to debug CFront with adb, understands what I'm referring to. Yours-who-nearly-started-programming-"C"-when-it-was-"B", -Gary-

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[boost] [Boost-bugs] [ boost-Bugs-931852 ] in the config.hpp system, problem with macos.hpp
by SourceForge.net 08 Apr '04

08 Apr '04

Bugs item #931852, was opened at 2004-04-08 10:06 Message generated for change (Tracker Item Submitted) made by Item Submitter You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=107586&aid=931852&group_i… Category: None Group: None Status: Open Resolution: None Priority: 5 Submitted By: Nobody/Anonymous (nobody) Assigned to: Nobody/Anonymous (nobody) Summary: in the config.hpp system, problem with macos.hpp Initial Comment: on MacOSX with a ProjectBuilder, the line # ifndef TARGET_CARBON # include <boost/config/posix_features.hpp> # endif does not work, because the posix_features are always activated, even with carbon targets. the guy probably wanted to do something like # ifndef __MACHO__ # include <boost/config/posix_features.hpp> # endif or something like that. that bug prevents the boost library to be used with ProjectBuilder's projects that uses Carbon. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=107586&aid=931852&group_i… ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Boost-bugs mailing list Boost-bugs(a)lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/boost-bugs

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