I want to make a basic library management system in prolog. The program should answer queries like which book is issued by which student and which date book will be returned. I want guidance in terms what exact components i need to learn for it (as I am very much new to prolog), i wanna develop it rapidly as i dun have time to learn the whole thing. I will be using visual prolog 7.3
Thanks in Advance
MGD
You haven't given us much of an idea what your programming background is, so I've interpolated a couple of comments below to suggest what existing experience might help in doing parts of the Visual-Prolog application asked about.
With Visual-Prolog you have to begin with user-interface design, something that I frankly found discouraging for playing around with the Prolog coding. Think of the "window" elements you want: perhaps an input field to input a user name and another input field to enter a book title, with some buttons for "search" as your "program should answer queries" spec suggests. The output will contain information about whether a book is checked out, when it is due, etc.
Then the functional part of your design can begin. Visual-Prolog asks you to declare certain things: domains (equivalent to datatypes in other languages) and predicates (the names relations and the domains to which their various arguments apply, roughly the equivalent to routines in other languages).
Your library application sounds like it is similar to a database, a "knowledge-base" containing information about users, books, and the relationship between them (e.g. this user has this book checked out), possibly with some history (who checked out a book when, and when was it returned).
Since you want to "develop it rapidly", you will probably want to start with a very simple set of domains and predicates. Perhaps "user" and "book" are the basic domains to start with, and checkOut/2 the basic predicate (indicating the fact that a particular user currently has the particular book). Then you will probably need to add (at least) the feature of storing the book's return date. This kind of design will be easier if you've done some relational database development before.
Connecting the user-interface (UI) to the "knowledge-base" of library users & books is a matter of writing predicates that serve as event-handlers for the visual elements of the UI. This is somewhat easier if you are familiar with Visual Basic. In any case you can "stub out" the event handlers while you are building the "look and feel" part of the UI, replacing them with substantive implementations as your design moves into developing the "knowledge-base".
As a designer, I like providing interfaces that cater to a power/simplicity balance. For example, I think the LINQ designers followed that principle because they offered both dot-notation and query-notation. The first is more powerful, but the second is easier to read and follow. If you disagree with my assessment of LINQ, please try to see my point anyway; LINQ was just an example, my post is not about LINQ.
I call this principle "dial-able power". But I'd like to know what other people call it. Certainly some will say "KISS" is the common term. But I see KISS as a superset, or a "consumerism" practice. Using LINQ as my example again, in my view, a team of programmers who always try to use query notation over dot-notation are practicing KISS. Thus the LINQ designers practiced "dial-able power", whereas the LINQ consumers practice KISS. The two make beautiful music together.
edit I'll give another example. Imagine a logging tool that has two signatures allowing two uses:
void Write(string message);
void Write(Func<string> messageCallback);
The purpose of the two signatures is to fulfill these needs:
//Every-day "simple" usage, nothing special.
myLogger.Write("Something Happened" + error.ToString() );
//This is performance critical, do not call ToString() if logging is
//disabled.
myLogger.Write( () => { "Something Happened" + error.ToString() });
Having these overloads represents "dial-able power," because the consumer has the choice of a simple interface or a powerful interface. A KISS-loving consumer will use the simpler signature most of the time, and will allow the "busy" looking signature when the power is needed. This also helps self-documentation, because usage of the powerful signature tells the reader that the code is performance critical. If the logger had only the powerful signature, then there would be no "dial-able power."
So this comes full-circle. I'm happy to keep my own "dial-able power" coinage if none yet exists, but I can't help think I'm missing an obvious designation for this practice.
p.s. Another example that is related, but is not the same as "dial-able power", is Scott Meyer's principle "make interfaces easy to use correctly, and hard to use incorrectly."
If your "dial" has only two positions/levels, it sounds like you're simply referring to a façade.
"Progressive disclosure."
You may already be acquainted with the term because of its use with user interfaces -- e.g., "More" buttons. However, the concept is more general.
From "Universal Principles of Design," by Lidwell, Holden and Butler:
Progressive disclosure involves separating information into
multiple layers and only presenting layers that are necessary or relevant.
I call this principle "dial-able
power". But I'd like to know what
other people call it.
I've personally never heard of "dial-able power", and I don't think its an industry standard term.
In the case of LINQ, we'd refer to its design as a fluent interface.
Fluent interfaces are design so that all methods on an object return the same type as that object, and therefore makes method chaining easy. You see the same fluent design in the StringBuilder.Append overloads, fluent NHibernate, and RhinoMocks.
In the case of JQuery, it also uses fluent interfaces for method chaining, but I believe "query" or "DSL" is the proper name for its selector notation.
(Obj-C selectors use the same terminology, but describe something completely different.)
Since its described as a querying DSL, most people can infer that it takes a sequence as input and returns a sequence as output. The query notation is performs roughly the same function as XPath with more bells and whistles.
Hibernate HQL is a querying DSL on top of many SQL dialects, and in a very superficial way regexes are a querying DSL which transform string sequences into a new set of string sequences (you can, in principle, make a fluent interface for regexes, but it would probably make you claw your eyes out).
I need to write a GUI app in Ruby that supports easily changing the text color for items in a listbox (ownerdraw) on Linux.
What GUI framework is recommended?
Shoes
Nobody knows shoes
http://shoooes.net/
It's by _why, so it's zany, but very usable.
Sorry for the super late answer, but in case anyone's wondering:
If you're using JRuby, I think Monkeybars should work for this. I'm 100% sure, first-hand, that it works for general list box manipulation, but what I'm not 100% sure about is whether it has complete functionality. Also not 100% on how perfectly it would work with Ownerdraw listboxes; I used typical Java-defined-netbeans-built boxes for simplicity's sake.
I didn't however, allow users to select multiple of the lines from the list (i.e. ctrl or shift + click). I remember that was working in some ways, but was giving me some trouble as far as passing functions. If I recall correctly, the biggest issue I was having with this, actually, was deciding how I wanted to manage requests to reorder the list while they had many things selected (E.G. if they clicked the shift-down or shift-up buttons while holding many elements). But other than that I think it worked fine.
From what I've seen using both, it's a bit more complicated to set up than shoes, but I found it to be very rewarding (at least as far as a simple school assignment was concerned, where I was required to have a GUI, but wanted to start learning Ruby, so I opted for a Java Swing front end to JRuby).
I certainly wouldn't be the best source for help setting it up and getting all your functions to work, and unfortunately there is minimal information about Monkeybars floating around, especially with regards to specialized "how do I do X?" kinds of questions, but there are boards available (links below) with very friendly and helpful posters. Much like here :)
http://groups.google.com/group/monkeybars-mvc/topics
*looks like the Kenai page has been abandoned and moved to the above google group and github
They also force a MVC architecture - so if you're going to use Monkeybars, you need to design your program to be compatible with this style. I never really saw this as a big deal, but I'm sure some people would dread being told how to structure their code.
So it's important to consider whether those are deal breakers before going through the trouble of installing the Monkeybars tools on your computer, but if you can deal with the few issues associated with it, Monkeybars can be a fantastic tool for building (and perhaps more importantly - manipulating) GUI around a JRuby project.
EDIT: here's some very basic example code using Moneybars:
define_signal :add_element, :add_element
def add_element(model, transfer)
trackList.getModel().addElement(model.addable.to_s)
end
where "trackList" was simply what the list was called on the Java end of the code (so "trackList.getModel()" would return the listbox model holding the list [for this project I needed 7 distinct lists to share a listbox, and to be switched between via drop-down list; if you only wanted one list to use the listbox you could just call it by name and remove the ".getModel()" part]. "addable" was the name of the well-fomatted element/string that I wanted to add to the list, and "model" (lower case) was the 'model' class used to conform to MVC architecture.
Sorry about the ugly signal part at the top, I had heavy deadlines and not enough time to play around with the variable names to use them better. It worked, and that was what mattered at the time (unfortunately). I'm reasonably sure the first one was the name of the signal (sent from the 'control' class) and the second one was probably a reference to the definition immediately following it. Sorry about my ignorance here, but it just made life easier to leave it as was (i.e. as was explained in the Monkeybars example code).
But there you have it, a function for adding elements to a GUI listbox using JRuby and Swing. It automatically redraws the screen when these signals are sent, so that's taken care of too. Right after that def is called you would see the changes. Modifying other aspects of the listbox were just as simple. Hope that helps anyone :)
The best way to go is visualruby:
http://visualruby.net
The code would look something like this:
#view = VR::ListView.new(:name => String, :address => String)
#view.ren_background(:name => "red")
#view.add_row(:name => "Hank", :address => "123 main")
That would make the background red for the name column. The #view variable would be used to populate a spot in the gui form.
I am writing a coding standards document for a team of about 15 developers with a project load of between 10 and 15 projects a year. Amongst other sections (which I may post here as I get to them) I am writing a section on code formatting. So to start with, I think it is wise that, for whatever reason, we establish some basic, consistent code formatting/naming standards.
I've looked at roughly 10 projects written over the last 3 years from this team and I'm, obviously, finding a pretty wide range of styles. Contractors come in and out and at times, and sometimes even double the team size.
I am looking for a few suggestions for code formatting and naming standards that have really paid off ... but that can also really be justified. I think consistency and shared-patterns go a long way to making the code more maintainable ... but, are there other things I ought to consider when defining said standards?
How do you lineup parenthesis? Do you follow the same parenthesis guidelines when dealing with classes, methods, try catch blocks, switch statements, if else blocks, etc.
Do you line up fields on a column? Do you notate/prefix private variables with an underscore? Do you follow any naming conventions to make it easier to find particulars in a file? How do you order the members of your class?
What about suggestions for namespaces, packaging or source code folder/organization standards? I tend to start with something like:
<com|org|...>.<company>.<app>.<layer>.<function>.ClassName
I'm curious to see if there are other, more accepted, practices than what I am accustomed to -- before I venture off dictating these standards. Links to standards already published online would be great too -- even though I've done a bit of that already.
First find a automated code-formatter that works with your language. Reason: Whatever the document says, people will inevitably break the rules. It's much easier to run code through a formatter than to nit-pick in a code review.
If you're using a language with an existing standard (e.g. Java, C#), it's easiest to use it, or at least start with it as a first draft. Sun put a lot of thought into their formatting rules; you might as well take advantage of it.
In any case, remember that much research has shown that varying things like brace position and whitespace use has no measurable effect on productivity or understandability or prevalence of bugs. Just having any standard is the key.
Coming from the automotive industry, here's a few style standards used for concrete reasons:
Always used braces in control structures, and place them on separate lines. This eliminates problems with people adding code and including it or not including it mistakenly inside a control structure.
if(...)
{
}
All switches/selects have a default case. The default case logs an error if it's not a valid path.
For the same reason as above, any if...elseif... control structures MUST end with a default else that also logs an error if it's not a valid path. A single if statement does not require this.
In the occasional case where a loop or control structure is intentionally empty, a semicolon is always placed within to indicate that this is intentional.
while(stillwaiting())
{
;
}
Naming standards have very different styles for typedefs, defined constants, module global variables, etc. Variable names include type. You can look at the name and have a good idea of what module it pertains to, its scope, and type. This makes it easy to detect errors related to types, etc.
There are others, but these are the top off my head.
-Adam
I'm going to second Jason's suggestion.
I just completed a standards document for a team of 10-12 that work mostly in perl. The document says to use "perltidy-like indentation for complex data structures." We also provided everyone with example perltidy settings that would clean up their code to meet this standard. It was very clear and very much industry-standard for the language so we had great buyoff on it by the team.
When setting out to write this document, I asked around for some examples of great code in our repository and googled a bit to find other standards documents that smarter architects than I to construct a template. It was tough being concise and pragmatic without crossing into micro-manager territory but very much worth it; having any standard is indeed key.
Hope it works out!
It obviously varies depending on languages and technologies. By the look of your example name space I am going to guess java, in which case http://java.sun.com/docs/codeconv/ is a really good place to start. You might also want to look at something like maven's standard directory structure which will make all your projects look similar.
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For those of you in the Visual Studio environment, how do you feel about wrapping any of your code in #regions? (or if any other IDE has something similar...)
9 out of 10 times, code folding means that you have failed to use the SoC principle for what its worth.
I more or less feel the same thing about partial classes. If you have a piece of code you think is too big you need to chop it up in manageable (and reusable) parts, not hide or split it up.It will bite you the next time someone needs to change it, and cannot see the logic hidden in a 250 line monster of a method.
Whenever you can, pull some code out of the main class, and into a helper or factory class.
foreach (var item in Items)
{
//.. 100 lines of validation and data logic..
}
is not as readable as
foreach (var item in Items)
{
if (ValidatorClass.Validate(item))
RepositoryClass.Update(item);
}
My $0.02 anyways.
This was talked about on Coding Horror.
My personal belief is that is that they are useful, but like anything in excess can be too much.
I use it to order my code blocks into:
Enumerations
Declarations
Constructors
Methods
Event Handlers
Properties
Sometimes you might find yourself working on a team where #regions are encouraged or required. If you're like me and you can't stand messing around with folded code you can turn off outlining for C#:
Options -> Text Editor -> C# -> Advanced Tab
Uncheck "Enter outlining mode when files open"
I use #Region to hide ugly and useless automatically generated code, which really belongs in the automatically generated part of the partial class. But, when working with old projects or upgraded projects, you don't always have that luxury.
As for other types of folding, I fold Functions all the time. If you name the function well, you will never have to look inside unless you're testing something or (re-)writing it.
While I understand the problem that Jeff, et. al. have with regions, what I don't understand is why hitting CTRL+M,CTRL+L to expand all regions in a file is so difficult to deal with.
I use Textmate (Mac only) which has Code folding and I find it really useful for folding functions, I know what my "getGet" function does, I don't need it taking up 10 lines of oh so valuable screen space.
I never use it to hide a for loop, if statement or similar unless showing the code to someone else where I will hide code they have seen to avoid showing the same code twice.
I prefer partial classes as opposed to regions.
Extensive use of regions by others also give me the impression that someone, somewhere, is violating the Single Responsibility Principle and is trying to do too many things with one object.
#Tom
Partial classes are provided so that you can separate tool auto-generated code from any customisations you may need to make after the code gen has done its bit. This means your code stays intact after you re-run the codegen and doesn't get overwritten. This is a good thing.
I'm not a fan of partial classes - I try to develop my classes such that each class has a very clear, single issue for which it's responsible. To that end, I don't believe that something with a clear responsibility should be split across multiple files. That's why I don't like partial classes.
With that said, I'm on the fence about regions. For the most part, I don't use them; however, I work with code every day that includes regions - some people go really heavy on them (folding up private methods into a region and then each method folded into its own region), and some people go light on them (folding up enums, folding up attributes, etc). My general rule of thumb, as of now, is that I only put code in regions if (a) the data is likely to remain static or will not be touched very often (like enums), or (b) if there are methods that are implemented out of necessity because of subclassing or abstract method implementation, but, again, won't be touched very often.
Regions must never be used inside methods. They may be used to group methods but this must be handled with extreme caution so that the reader of the code does not go insane. There is no point in folding methods by their modifiers. But sometimes folding may increase readability. For e.g. grouping some methods that you use for working around some issues when using an external library and you won't want to visit too often may be helpful. But the coder must always seek for solutions like wrapping the library with appropriate classes in this particular example. When all else fails, use folding for improving readibility.
This is just one of those silly discussions that lead to nowhere. If you like regions, use them. If you don't, configure your editor to turn them off. There, everybody is happy.
I generally find that when dealing with code like Events in C# where there's about 10 lines of code that are actually just part of an event declaration (the EventArgs class the delegate declaration and the event declaration) Putting a region around them and then folding them out of the way makes it a little more readable.
Region folding would be fine if I didn't have to manually maintain region groupings based on features of my code that are intrinsic to the language. For example, the compiler already knows it's a constructor. The IDE's code model already knows it's a constructor. But if I want to see a view of the code where the constructors are grouped together, for some reason I have to restate the fact that these things are constructors, by physically placing them together and then putting a group around them. The same goes for any other way of slicing up a class/struct/interface. What if I change my mind and want to see the public/protected/private stuff separated out into groups first, and then grouped by member kind?
Using regions to mark out public properties (for example) is as bad as entering a redundant comment that adds nothing to what is already discernible from the code itself.
Anyway, to avoid having to use regions for that purpose, I wrote a free, open source Visual Studio 2008 IDE add-in called Ora. It provides a grouped view automatically, making it far less necessary to maintain physical grouping or to use regions. You may find it useful.
I think that it's a useful tool, when used properly. In many cases, I feel that methods and enumerations and other things that are often folded should be little black boxes. Unless you must look at them for some reason, their contents don't matter and should be as hidden as possible. However, I never fold private methods, comments, or inner classes. Methods and enums are really the only things I fold.
My approach is similar to a few others here, using regions to organize code blocks into constructors, properties, events, etc.
There's an excellent set of VS.NET macros by Roland Weigelt available from his blog entry, Better Keyboard Support for #region ... #endregion. I've been using these for years, mapping ctrl+. to collapse the current region and ctrl++ to expand it. Find that it works a lot better that the default VS.NET functionality which folds/unfolds everything.
I personally use #Regions all the time. I find that it helps me to keep things like properties, declarations, etc separated from each other.
This is probably a good answer, too!
Coding Horror
Edit: Dang, Pat beat me to this!
The Coding Horror article actual got me thinking about this as well.
Generally, I large classes I will put a region around the member variables, constants, and properties to reduce the amount of text I have to scroll through and leave everything else outside of a region. On forms I will generally group things into "member variables, constants, and properties", form functions, and event handlers. Once again, this is more so I don't have to scroll through a lot of text when I just want to review some event handlers.
I prefer #regions myself, but an old coworker couldn't stand to have things hidden. I understood his point once I worked on a page with 7 #regions, at least 3 of which had been auto-generated and had the same name, but in general I think they're a useful way of splitting things up and keeping everything less cluttered.
I really don't have a problem with using #region to organize code. Personally, I'll usually setup different regions for things like properties, event handlers, and public/private methods.
Eclipse does some of this in Java (or PHP with plugins) on its own. Allows you to fold functions and such. I tend to like it. If I know what a function does and I am not working on it, I dont need to look at it.
Emacs has a folding minor mode, but I only fire it up occasionally. Mostly when I'm working on some monstrosity inherited from another physicist who evidently had less instruction or took less care about his/her coding practices.
Using regions (or otherwise folding code) should have nothing to do with code smells (or hiding them) or any other idea of hiding code you don't want people to "easily" see.
Regions and code folding is really all about providing a way to easily group sections of code that can be collapsed/folded/hidden to minimize the amount of extraneous "noise" around what you are currently working on. If you set things up correctly (meaning actually name your regions something useful, like the name of the method contained) then you can collapse everything except for the function you are currently editing and still maintain some level of context without having to actually see the other code lines.
There probably should be some best practice type guidelines around these ideas, but I use regions extensively to provide a standard structure to my code files (I group events, class-wide fields, private properties/methods, public properties/methods). Each method or property also has a region, where the region name is the method/property name. If I have a bunch of overloaded methods, the region name is the full signature and then that entire group is wrapped in a region that is just the function name.
I personally hate regions. The only code that should be in regions in my opinion is generated code.
When I open file I always start with Ctrl+M+O. This folds to method level. When you have regions you see nothing but region names.
Before checking in I group methods/fields logically so that it looks ok after Ctrl+M+O.
If you need regions you have to much lines in your class. I also find that this is very common.
region ThisLooksLikeWellOrganizedCodeBecauseIUseRegions
// total garbage, no structure here
endregion
Enumerations
Properties
.ctors
Methods
Event Handlers
That's all I use regions for. I had no idea you could use them inside of methods.
Sounds like a terrible idea :)