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  • Any language where every class instance is a class too?

    - by Dokkat
    Taking inspiration from Javascript prototypes, I had the idea of a language where every instance can be used as a class. Before I potentially reinvent the wheel, I would like to ask if there is a language already using this concept: //To declare a Class, extend the base class (in this case, Type) Type(Weapon,{price:0}); //Same syntax to inherit; simply extend the parent: Weapon(Sword,{price:3}); Weapon(Axe,{price:4}); Sword(Katana,{price:7}); Sword(Dagger,{price:3}); //And the same to create an instance: Katana(myKatana,{nickname:"Leon"}); myKatana.price; // 7 myKatana.nickname; // Leon // An operator to return children of a class; Sword_; // [Katana, Dagger] // An operator to return array of descendants; Sword__; // [Katana, Dagger, myKatana] // An operator to return array of parents; Sword^; // Weapon // Arrays can be used as elements Sword__.price += 1; //increases price of Sword's descendants by 1 mySword.price; //8 // And to access specific element (using its name instead of index) var name = "mySword" Katana_[name]; // [mySword] Katana_[name].nickname; // Leon Has this kind of approach been already studied/implemented?

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  • Is sexist humor more common in the Ruby community than other language communities? [closed]

    - by Andrew Grimm
    I've heard of more cases of sexist humor in the Ruby community, such as the sqoot's "women as perk" and toplessness in advertising, than in all the other programming language communities combined. Is this merely because I'm in the Ruby community, and therefore are more likely to hear about incidents in the Ruby community, or is it because there's a higher rate of sexist humor in the Ruby community compared to, say, the C community?

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  • Error Copying Source File in Audio Spectrum Visualizer [closed]

    - by David Dimalanta
    I'm testing this code using LibGDX, Java, and Eclipse to test the music player that detects the frequency. I saw this one on this website plus the link on GitHub: http://gtomee.com/2012/07/28/audio-spectrum-visualizer-with-libgdx/ It works when running on desktop project folder but not on Android project folder and the result is this: 10-10 13:57:45.320: E/AndroidRuntime(9421): FATAL EXCEPTION: GLThread 16845 10-10 13:57:45.320: E/AndroidRuntime(9421): com.badlogic.gdx.utils.GdxRuntimeException: Error copying source file: soundtrack 1 bioman.mp3 (Internal) 10-10 13:57:45.320: E/AndroidRuntime(9421): To destination: tmp/audio-spectrum.mp3 (External) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.copyFile(FileHandle.java:625) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.copyTo(FileHandle.java:534) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.bodapps.rhythm.Drop.create(Drop.java:393) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.backends.android.AndroidGraphics.onSurfaceChanged(AndroidGraphics.java:292) 10-10 13:57:45.320: E/AndroidRuntime(9421): at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1505) 10-10 13:57:45.320: E/AndroidRuntime(9421): at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1240) 10-10 13:57:45.320: E/AndroidRuntime(9421): Caused by: com.badlogic.gdx.utils.GdxRuntimeException: Error stream writing to file: tmp/audio-spectrum.mp3 (External) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.write(FileHandle.java:313) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.copyFile(FileHandle.java:623) 10-10 13:57:45.320: E/AndroidRuntime(9421): ... 5 more 10-10 13:57:45.320: E/AndroidRuntime(9421): Caused by: com.badlogic.gdx.utils.GdxRuntimeException: Error writing file: tmp/audio-spectrum.mp3 (External) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.write(FileHandle.java:293) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.write(FileHandle.java:305) 10-10 13:57:45.320: E/AndroidRuntime(9421): ... 6 more 10-10 13:57:45.320: E/AndroidRuntime(9421): Caused by: java.io.FileNotFoundException: /storage/sdcard0/tmp/audio-spectrum.mp3: open failed: EACCES (Permission denied) 10-10 13:57:45.320: E/AndroidRuntime(9421): at libcore.io.IoBridge.open(IoBridge.java:416) 10-10 13:57:45.320: E/AndroidRuntime(9421): at java.io.FileOutputStream.<init>(FileOutputStream.java:88) 10-10 13:57:45.320: E/AndroidRuntime(9421): at com.badlogic.gdx.files.FileHandle.write(FileHandle.java:289) 10-10 13:57:45.320: E/AndroidRuntime(9421): ... 7 more 10-10 13:57:45.320: E/AndroidRuntime(9421): Caused by: libcore.io.ErrnoException: open failed: EACCES (Permission denied) 10-10 13:57:45.320: E/AndroidRuntime(9421): at libcore.io.Posix.open(Native Method) 10-10 13:57:45.320: E/AndroidRuntime(9421): at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110) 10-10 13:57:45.320: E/AndroidRuntime(9421): at libcore.io.IoBridge.open(IoBridge.java:400) 10-10 13:57:45.320: E/AndroidRuntime(9421): ... 9 more I'm not sure if I come this to the right place for help and suggestions.

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  • How best to deal with the frustration that you encounter at the beginning of learning to code [closed]

    - by coderboy
    I am right now a newbie on the job learning to code in Cocoa . In the beginning I decided that I would try and understand everything I was doing . But right now I just feel like a clueless wizard chanting some spells . Its all just a matter of googling the right incantation . Frequently getting stuck and having to google for answers is proving to be a major demotivator for me . I know that this will get better over time but still I feel that somewhere , somehow I'm just approaching things the wrong way . I sit there stumped and then finally just look at sample code from Apple and I go Wow ! This is so logical and well structured ! . But just reading it is not going to get me to that level . So I would like to know , how do you guys approach learning something new . Do you read the whole documentation first , or do you read sample code or maybe its just about making lots of small programs first ?

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  • Why can't we capture the design of software more effectively?

    - by Ira Baxter
    As engineers, we all "design" artifacts (buildings, programs, circuits, molecules...). That's an activity (design-the-verb) that produces some kind of result (design-the-noun). I think we all agree that design-the-noun is a different entity than the artifact itself. A key activity in the software business (indeed, in any business where the resulting product artifact needs to be enhanced) is to understand the "design (the-noun)". Yet we seem, as a community, to be pretty much complete failures at recording it, as evidenced by the amount of effort people put into rediscovering facts about their code base. Ask somebody to show you the design of their code and see what you get. I think of a design for software as having: An explicit specification for what the software is supposed to do and how well it does it An explicit version of the code (this part is easy, everybody has it) An explanation for how each part of the code serves to achieve the specification A rationale as to why the code is the way it is (e.g., why a particualr choice rather than another) What is NOT a design is a particular perspective on the code. For example [not to pick specifically on] UML diagrams are not designs. Rather, they are properties you can derive from the code, or arguably, properties you wish you could derive from the code. But as a general rule, you can't derive the code from UML. Why is it that after 50+ years of building software, why don't we have regular ways to express this? My personal opinion is that we don't have good ways to express this. Even if we do, most of the community seems so focused on getting "code" that design-the-noun gets lost anyway. (IMHO, until design becomes the purpose of engineering, with the artifact extracted from the design, we're not going to get around this). What have you seen as means for recording designs (in the sense I have described it)? Explicit references to papers would be good. Why do you think specific and general means have not been succesful? How can we change this?

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  • What are the canonical problem sets or problem domains for the different types of languages?

    - by SnOrfus
    I'm just wondering what some of the canonical problem sets are for certain types of languages? ie. Fill in the blanks: __ is the perfect language to use for solving __. The question was arrived at reading or hearing people say statements like such and such module in our codebase would be much easier to implement using a functional language. Fee free to include examples that would seem obvious to you.

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  • Lightweight, dynamic, fully JavaScript web UI library recommendations

    - by Matt Greer
    I am looking for recommendations for a lightweight, dynamic, fully JavaScript UI library for websites. Doesn't have to be amazing visually, the end result is for simple demos I create. What I want can be summed up as "Ext-like, but not GPL'ed, and a much smaller footprint". I want to be able to construct UIs dynamically and fully through code. My need for this is currently driven by this particle designer. Depending on what query parameters you give it, the UI components change, example 1, example2. Currently this is written in Ext, but Ext's license and footprint are turn offs for me. I like UKI a lot, but it's not very good for dynamically building UIs since everything is absolutely positioned. Extending Uki to support that is something I am considering. Ideally the library would let me make UIs with a pattern along the lines of: var container = new SomeUI.Container(); container.add(new SomeUI.Label('Color Components')); container.add(new SomeUI.NumberField('R')); container.add(new SomeUI.NumberField('G')); container.add(new SomeUI.NumberField('B')); container.add(new SomeUI.CheckBox('Enable Alpha')); container.renderTo(someDiv);

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  • Immutable Method in Java

    - by Chris Okyen
    In Java, there is the final keyword in lieu of the const keyword in C and C++. In the latter languages there are mutable and immutable methods such as stated in the answer by Johannes Schaub - litb to the question How many and which are the uses of “const” in C++? Use const to tell others methods won't change the logical state of this object. struct SmartPtr { int getCopies() const { return mCopiesMade; } }ptr1; ... int var = ptr.getCopies(); // returns mCopiesMade and is specified that to not modify objects state. How is this performed in Java?

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  • When and why you should use void (instead of i.e. bool/int)

    - by Jonas
    I occasionally run into methods where a developer chose to return something which isn't critical to the function. I mean, when looking at the code, it apparently works just as nice as a void and after a moment of thought, I ask "Why?" Does this sound familiar? Sometimes I would agree that most often it is better to return something like a bool or int, rather then just do a void. I'm not sure though, in the big picture, about the pros and cons. Depending on situation, returning an int can make the caller aware of the amount of rows or objects affected by the method (e.g., 5 records saved to MSSQL). If a method like "InsertSomething" returns a boolean, I can have the method designed to return true if success, else false. The caller can choose to act or not on that information. On the other hand, May it lead to a less clear purpose of a method call? Bad coding often forces me to double-check the method content. If it returns something, it tells you that the method is of a type you have to do something with the returned result. Another issue would be, if the method implementation is unknown to you, what did the developer decide to return that isn't function critical? Of course you can comment it. The return value has to be processed, when the processing could be ended at the closing bracket of method. What happens under the hood? Did the called method get false because of a thrown error? Or did it return false due to the evaluated result? What are your experiences with this? How would you act on this?

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  • C Problem with Compiler?

    - by Solomon081
    I just started learning C, and wrote my hello world program: #include <stdio.h> main() { printf("Hello World"); return 0; } When I run the code, I get a really long error: Apple Mach-O Linker (id) Error Ld /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj normal x86_64 cd /Users/Solomon/Desktop/C/CProj setenv MACOSX_DEPLOYMENT_TARGET 10.7 /Developer/usr/bin/clang -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.7.sdk -L/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -F/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -filelist /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/CProj.LinkFileList -mmacosx-version-min=10.7 -o /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj ld: duplicate symbol _main in /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/helloworld.o and /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/main.o for architecture x86_64 Command /Developer/usr/bin/clang failed with exit code 1 I am running xCode Should I reinstall DevTools?

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  • Python as a first language?

    - by user64085
    I have just started working in Information Security World. I want to learn the Python language for creating my own automated tool for Fuzzing, SQL-Injection etc. My question is I don't know much about C language (only basic knowledge) but I want to learn directly Python Language so is it good? I have seen there is lots of difference between Python and C (obviously) and for Information Security field Python = GOD so I want to know learning Python need any experience on C language? If not so can I start learning Python directly?

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  • Computer vision algorithms (how is this possible?)

    - by Maxim Gershkovich
    I recently stumbled across a company that has created what appears to be a computer vision technology that is capable of detecting shoplifting automatically and alert its users. LINK Watching some of the videos and examples provided by the company has left me completely baffled and amazed as to how on earth they may have achieved this functionality. I understand that no-one here will be able to tell me exactly how this may have been achieved but is anyone aware - and could point me to - research in this field or alternatively perhaps provide details as to how something like this could be implemented or guidance of where one might start? My understanding was the computer vision algorithms were many years away from being this sophisticated. Is this sort of application really possible? Anyone willing to hazard a guess at how they achieved this?

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  • Simplified knapsack in PHP

    - by Mikhail
    I have two instances where I'd like to display information in a "justified" alignment - but I don't care if the values are switched in order. One example being displaying the usernames of people online: Anton Brother68 Commissar Dougheater Elflord Foobar Goop Hoo Iee Joo Rearranging them we could get exactly 22 characters long on each line: Anton Brother68 Foobar Commissar Elflord Goop Dougheater Hoo Iee Joo This is kind of a knapsack, except seems like there ought to be a P solution since I don't care about perfection, and I have multiple lines. Second instance is identical, except instead of names and character count I would be displaying random images and use their width.

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  • Is there an open source license for this?

    - by Philip
    I have written code at home, on my own time and using my own knowledge and equipment, while under no contract or NDA. I want to make this code open source so that I can use it in software I write for an employer, without denying myself the right to use it at home or elsewhere later. I'm not sure if saying it is in the "public domain" would fit this purpose, or if I need to find an open source license. I want anyone to be able to use the code in closed source proprietary software with zero requirements for including a license with the source or binary. And I want to minimize the risk of anyone being sued for using it. (I'm aware that one can never be 100% safe from being sued.) Is there an open source license that fits this purpose? To what extent is what I want to do even possible? I wouldn't mind putting the license in comments in the code files themselves, but that obviously doesn't go with the binary.

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  • Detail of acceptance criteria in user story

    - by Kai Kramhoeft
    I have the following example for a user story with acceptance criteria. I would like to know if I am allowed to describe how the GUI must be changed to support the new feature. How much detail can acceptance criteria have? This is my example: User Story: As forum administrator I will connect persons in groups, so that people can get organized. Acceptance Criteria: The creation of a person group happens below a person group pool (person group pool is an object also visually available in the current software system) The creation happens with a context menu of the persongroup pool. Below the pool one can create new groups. A person group contains: person group-ID, description, remark May that be relevant an right acceptance criteria? Because I describe how you can create a new group by opening a context menu.

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  • Bitbucket and a small development house

    - by Marlon
    I am in the process of finally rolling Mercurial as our version control system at work. This is a huge deal for everyone as, shockingly, they have never used a VCS. After months of putting the bug in management's ears, they finally saw the light and now realise how much better it is than working with a network of shared folders! In the process of rolling this out, I am thinking of different strategies to manage our stuff and I am leaning towards using Bitbucket as our "central" repository. The projects in Bitbucket will solely be private projects and everyone will push and pull from there. I am open to different suggestions, but has anyone got a similar setup? If so, what caveats have you encountered?

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  • Staying OO and Testable while working with a database

    - by Adam Backstrom
    What are some OOP strategies for working with a database but keeping thing testable? Say I have a User class and my production environment works against MySQL. I see a couple possible approaches, shown here using PHP: Pass in a $data_source with interfaces for load() and save(), to abstract the backend source of data. When testing, pass a different data store. $user = new User( $mysql_data_source ); $user-load( 'bob' ); $user-setNickname( 'Robby' ); $user-save(); Use a factory that accesses the database and passes the result row to User's constructor. When testing, manually generate the $row parameter, or mock the object in UserFactory::$data_source. (How might I save changes to the record?) class UserFactory { static $data_source; public static function fetch( $username ) { $row = self::$data_source->get( [params] ); $user = new User( $row ); return $user; } } I have Design Patterns and Clean Code here next to me, but I'm struggling to find applicable concepts.

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  • How to manage an issue tracker's backlog

    - by Josh Kelley
    We've been dutifully using Trac for several years now, and our "active tickets" list has grown to almost 200 items. These include bugs that are too low priority and too complicated to fix for now, feature requests that have been deferred, issues that have never really generated complaints but everyone agrees ought to be fixed someday, planned code refactorings and other design infelicities that we don't want to lose track of, etc. As a result, with almost 200 of these issues, the list is almost overwhelming; it's no longer useful as a source of what needs to be worked on right now. What's the best way to keep track of issues of this sort? Part of the problem is that some of these issues are such a low priority that they may never get done. I hate to lose track of these items (similar to not wanting to throw something out of my house in case I might need it someday); do I need to throw them out regardless (by marking them as wontfix) and assume I can find them in the future if I ever do need them?

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  • Does FFMpeg support gpu acceleration of media encoding/decoding?

    - by Jason123
    I was wondering if ffmpeg supported gpu acceleration. I was reading on their websites and came across contradicting information. http://www.ffmpeg.org/general.html#Video-Codecs -H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (VDPAU acceleration) http://ffmpeg.org/trac/ffmpeg/wiki/x264EncodingGuide -Will a graphics card make x264 encode faster? No. libx264 doesn't use them (at least not yet). There are some proprietary encoders that utilize the GPU, but that does not mean they are well optimized, though encoding time may be faster; and they might be worse than x264 anyway, and possibly slower. Regardless, FFmpeg today doesn't support any means of gpu encoding, outside of libx264. If not, is there any way to add gpu acceleration to h.264 encoding/decoding?

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  • How can I compare between web development technologies?

    - by Steve
    I would like experts to explain for me how can I compare between web development tools or technologies in order to be able to choose the right one. I'm tired from searching always in the regular way: X Technology vs Y Technology. I'm tired from peoples' biased opinions and usually I don't find a fair comparison. I have decided to put my question here about how can I compare them so you may identify to me the main standards for comparisons so I can compare them by myself and becoming able to choose the technology that is appropriate for the project I will develop. Note: in web development technologies I mean server side languages (e.g. PHP). One important requirement for me that can be defined as major one is cost efficiency and I mean that I don't care about the cost in the near future or the current cost, but what is more important for me is the cost in the future. If, for example, the site becomes one of the most 100 visited sites.   So, how can I compare the cost of different technologies for a future status of a site (such as being very famous site) so I can scale my option easily without missing a good technology like what happened with some sites when they chose not the most effective tool.

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  • Generic log analyzer that produces reports

    - by Eugene
    About 600 customers use our application. We have very detailed logs for everything that happens in the application, from changes in the data model, memory and CPU/GPU usage to clicks on the UI elements. We want to be able to parse the logs coming from these customers and analyze them to understand how users use our application and what happens internally in the application. Is there a log analyzer that can produce such reports automatically?

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  • Is it bad idea to use flag variable to search MAX element in array?

    - by Boris Treukhov
    Over my programming career I formed a habit to introduce a flag variable that indicates that the first comparison has occured, just like Msft does in its linq Max() extension method implementation public static int Max(this IEnumerable<int> source) { if (source == null) { throw Error.ArgumentNull("source"); } int num = 0; bool flag = false; foreach (int num2 in source) { if (flag) { if (num2 > num) { num = num2; } } else { num = num2; flag = true; } } if (!flag) { throw Error.NoElements(); } return num; } However I have met some heretics lately, who implement this by just starting with the first element and assigning it to result, and oh no - it turned out that STL and Java authors have preferred the latter method. Java: public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) { Iterator<? extends T> i = coll.iterator(); T candidate = i.next(); while (i.hasNext()) { T next = i.next(); if (next.compareTo(candidate) > 0) candidate = next; } return candidate; } STL: template<class _FwdIt> inline _FwdIt _Max_element(_FwdIt _First, _FwdIt _Last) { // find largest element, using operator< _FwdIt _Found = _First; if (_First != _Last) for (; ++_First != _Last; ) if (_DEBUG_LT(*_Found, *_First)) _Found = _First; return (_Found); } Are there any preferences between one method or another? Are there any historical reasons for this? Is one method more dangerous than another?

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  • Is mocking for unit testing appropriate in this scenario?

    - by Vinoth Kumar
    I have written around 20 methods in Java and all of them call some web services. None of these web services are available yet. To carry on with the server side coding, I hard-coded the results that the web-service is expected to give. Can we unit test these methods? As far as I know, unit testing is mocking the input values and see how the program responds. Are mocking both input and ouput values meaningful? Edit : The answers here suggest I should be writing unit test cases. Now, how can I write it without modifying the existing code ? Consider the following sample code (hypothetical code) : public int getAge() { Service s = locate("ageservice"); // line 1 int age = s.execute(empId); // line 2 return age; // line 3 } Now How do we mock the output ? Right now , I am commenting out 'line 1' and replacing line 2 with int age= 50. Is this right ? Can anyone point me to the right way of doing it ?

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  • mips number of clock cycles and how improving code

    - by Hooman
    I'm really new in MIPS and I have these questions which I found so many dissimil answers for them ... if someone can help, it would be great. Thanks How many clock cycles does this code take? #Macro Instructions li $t0, 32 # 1 or 2 cycles ? # lui $at, Upper 16-bits of value # ori Rd, $at, Lower 16-bits of value # ----------------------------------- # ori Rt, $0, value # # Which set of instructions will be executed? div $t2, $t2, $t0 # 41 cycles? # bne Rt, $0, # break $0 # ok: div Rs, Rt # mflo Rd #Integer Instruction lw $t2, 0($t13) # 1 cycles? sw $t2, 0($t3) # 1 cycles? How those 4 lines of codes can be significantly improved? by avoiding to use Macros or ... ?

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  • Type checking and recursive types (Writing the Y combinator in Haskell/Ocaml)

    - by beta
    When explaining the Y combinator in the context of Haskell, it's usually noted that the straight-forward implementation won't type-check in Haskell because of its recursive type. For example, from Rosettacode [1]: The obvious definition of the Y combinator in Haskell canot be used because it contains an infinite recursive type (a = a -> b). Defining a data type (Mu) allows this recursion to be broken. newtype Mu a = Roll { unroll :: Mu a -> a } fix :: (a -> a) -> a fix = \f -> (\x -> f (unroll x x)) $ Roll (\x -> f (unroll x x)) And indeed, the “obvious” definition does not type check: ?> let fix f g = (\x -> \a -> f (x x) a) (\x -> \a -> f (x x) a) g <interactive>:10:33: Occurs check: cannot construct the infinite type: t2 = t2 -> t0 -> t1 Expected type: t2 -> t0 -> t1 Actual type: (t2 -> t0 -> t1) -> t0 -> t1 In the first argument of `x', namely `x' In the first argument of `f', namely `(x x)' In the expression: f (x x) a <interactive>:10:57: Occurs check: cannot construct the infinite type: t2 = t2 -> t0 -> t1 In the first argument of `x', namely `x' In the first argument of `f', namely `(x x)' In the expression: f (x x) a (0.01 secs, 1033328 bytes) The same limitation exists in Ocaml: utop # let fix f g = (fun x a -> f (x x) a) (fun x a -> f (x x) a) g;; Error: This expression has type 'a -> 'b but an expression was expected of type 'a The type variable 'a occurs inside 'a -> 'b However, in Ocaml, one can allow recursive types by passing in the -rectypes switch: -rectypes Allow arbitrary recursive types during type-checking. By default, only recursive types where the recursion goes through an object type are supported. By using -rectypes, everything works: utop # let fix f g = (fun x a -> f (x x) a) (fun x a -> f (x x) a) g;; val fix : (('a -> 'b) -> 'a -> 'b) -> 'a -> 'b = <fun> utop # let fact_improver partial n = if n = 0 then 1 else n*partial (n-1);; val fact_improver : (int -> int) -> int -> int = <fun> utop # (fix fact_improver) 5;; - : int = 120 Being curious about type systems and type inference, this raises some questions I'm still not able to answer. First, how does the type checker come up with the type t2 = t2 -> t0 -> t1? Having come up with that type, I guess the problem is that the type (t2) refers to itself on the right side? Second, and perhaps most interesting, what is the reason for the Haskell/Ocaml type systems to disallow this? I guess there is a good reason since Ocaml also will not allow it by default even if it can deal with recursive types if given the -rectypes switch. If these are really big topics, I'd appreciate pointers to relevant literature. [1] http://rosettacode.org/wiki/Y_combinator#Haskell

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