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• Does "Value Restriction" practically mean that there is no higher order functional programming?

  - by Sadache

  Does "Value Restriction" practically mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" and I would like to know whether it is a problem of a prticular implementation of VR or it is a general problem that has no solution in a mutable type-infered language that doesn't include mutation in the type system.

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• c++ Array passing dilemma

  - by Thomas

  Hi, I am writing a function that takes a string, string pointer and an int. The function splits the string based on a set of rules and puts each token into an array. I need to return the array out of the function with the number of elements in the int variable etc. I am stuck as to how I return the array as I can not use auto other wise it is destroyed and I am reluctant to use new as I feel this is patchy. I have other ideas on how to go about this but would like to see how other people go about this first. I could also be wrong and it could be possible to pass an auto out of an array. I can also not use vectors so there goes a copy constructor.

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• Problem with variable argument function in C++

  - by Freezerburn

  I'm trying to create a variable length function (obviously, heh) in C++, and what I have right now works, but only for the first argument. If someone could please let me know how to get this working with all the arguments that are passed, I would really appreciate it. Code: void udStaticObject::accept( udObjectVisitor *visitor, ... ) { va_list marker; udObjectVisitor *i = visitor; va_start( marker, visitor ); while( 1 ) { i->visit_staticObject( this ); //the if here will always go to the break immediately, allowing only //one argument to be used if( ( i = va_arg( marker, udObjectVisitor* ) ) ) break; } va_end( marker ); } Based on my past posts, and any help posts I make in general, there is probably some information that I did not provide that you will need to know to help. I apologize in advance if I forgot anything, and please let me know what you need to know so I can provide the information.

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• Passing an array as a function parameter in JavaScript

  - by Robert

  Hi all, i'd like to call a function using an array as a parameters: var x = [ 'p0', 'p1', 'p2' ]; call_me ( x[0], x[1], x[2] ); // i don't like it function call_me (param0, param1, param2 ) { // ... } Is there a better way of passing the contents of x into call_me()? Ps. I can't change the signature of call_me(), nor the way x is defined. Thanks in advance

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• How to find the length of a parameter pack ?

  - by Eternal Learner

  Hi All, Suppose I have a variadic template function like template<typename... Args> unsigned length(Args... args); How do I find the length of the parameter list ?

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• include() Why should I not use it?

  - by aliov

  I am working through an older php mysql book written in 2003. The author uses the include() function to construct html pages by including header.inc, footer.inc, main.inc files, etc. Now I find out that this is not allowed in the default ini settings, (allow_url_include is set to Off) after I got many warnings from the server. I noticed also that you can use include without the parenthesis. I tried this and it works and I get no error messages or warnings. Are the two different? That is, is include() different from include ?

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• Assigning function within function object without invoking the function itself.

  - by webzide

  Dear experts, I am trying to assign an function within an function object property without actually invoking then function itself. for instance, I have the following function object class definition function objectOne(name, value, id){ this.name=name; this.value=value; this.id=id; this.methodOne=methodFunction(this); } the last line this.methodOne=methodFunction(this); I want to pass the current object to the function but at the same time i don't want to execute the function right now. But if I do it this way without the bracket this.methodOne=methodFunction then the argument of this object would not be passed as a parameter to the function. Is there a way to work through this. Thank you in advance

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• Postgresql - Edit function signature

  - by drave

  POSTGRESQL 8.4.3 - i created a function with this signature CREATE OR REPLACE FUNCTION logcountforlasthour() RETURNS SETOF record AS realised i wanted to change it to this CREATE OR REPLACE FUNCTION logcountforlasthour() RETURNS TABLE(ip bigint, count bigint) record AS but when i apply that change in the query tool it isnt accepted or rather it is accepted, there is no syntax error, but the text of the function has not been changed. even if i run "DROP FUNCTION logcountforlasthour()" between edits the old syntax comes back if i edit the body of the function, thats fine, it changes but not the signature is there something i'm missing thanks

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• Is return an operator or a function?

  - by eSKay

  This is too basic I think, but how do both of these work? return true; // 1 and return (true); // 2 Similar: sizeof, exit My guess: If return was a function, 1 would be erroneous. So, return should be a unary operator that can also take in brackets... pretty much like unary minus: -5 and -(5), both are okay. Is that what it is - a unary operator?

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• Dynamic creation of a pointer function in c++

  - by Liberalkid

  I was working on my advanced calculus homework today and we're doing some iteration methods along the lines of newton's method to find solutions to things like x^2=2. It got me thinking that I could write a function that would take two function pointers, one to the function itself and one to the derivative and automate the process. This wouldn't be too challenging, then I started thinking could I have the user input a function and parse that input (yes I can do that). But can I then dynamically create a pointer to a one-variable function in c++. For instance if x^2+x, can I make a function double function(double x){ return x*x+x;} during run-time. Is this remotely feasible, or is it along the lines of self-modifying code?

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• What are good uses for Python3's "Function Annotations"

  - by agscala

  Function Annotations: PEP-3107 I ran across a snippet of code demonstrating Python3's function annotations. The concept is simple but I can't think of why these were implemented in Python3 or any good uses for them. Perhaps SO can enlighten me? How it works: def foo(a: 'x', b: 5 + 6, c: list) -> max(2, 9): ... function body ... Everything following the colon after an argument is an 'annotation', and the information following the -> is an annotation for the function's return value. foo.func_annotations would return a dictionary: {'a': 'x', 'b': 11, 'c': list, 'return': 9} What's the significance of having this available?

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• If a Matlab function returns a variable number of values, how can I get all of them as a cellarray,

  - by kaleidomedallion

  I am writing a function to remove some values from a cellarray, like so: function left = remove(cells, item); left = cells{cellfun(@(i) ~isequal(item, i), cells)}; But when I run this, left has only the first value, as the call to cells{} with a logical array returns all of the matching cells as separate values. How do I group these separate return values into a single cellarray? Also, perhaps there is already a way to remove a given item from a cellarray? I could not find it in the documentation.

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• Toggle Image Overlays in Google Maps API v3

  - by Douglas

  Hey guys. I've been building a small library for myself for a job I have at the moment building a map for a university. I've gotten pretty well everything I need in some basic form, but one thing has simply not been working, and is simply not giving me results. The university itself is sort of in a partnership with the neighboring college. It's been decided that both campuses should be included. I need to be able to toggle on/off the overlays of the campuses individually. i.e. Start with all campuses ON. User then turns OFF college campus, university overlay stays up. User can then turn it back on to display the college once more, or turn off the university as well, leaving no overlays. Here's a work in progress I'm doing at the moment: http://bgsweb.ca/maps/generator.html Basically, we need to take the one overlay, split it into multiple overlays, and enable the toggling of each individual overlay. Any assistance much appreciated!

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• Template class + virtual function = must implement?

  - by sold

  This code: template <typename T> struct A { T t; void DoSomething() { t.SomeFunction(); } }; struct B { }; A<B> a; is easily compiled without any complaints, as long as I never call a.DoSomething(). However, if I define DoSomething as a virtual function, I will get a compile error saying that B doesn't declare SomeFunction. I can somewhat see why it happens (DoSomething should now have an entry in the vtable), but I can't help feeling that it's not really obligated. Plus it sucks. Is there any way to overcome this? EDIT 2: Okay. I hope this time it makes sence: Let's say I am doing intrusive ref count, so all entities must inherit from base class Object. How can I suuport primitive types too? I can define: template <typename T> class Primitive : public Object { T value; public: Primitive(const T &value=T()); operator T() const; Primitive<T> &operator =(const T &value); Primitive<T> &operator +=(const T &value); Primitive<T> &operator %=(const T &value); // And so on... }; so I can use Primitive<int>, Primitive<char>... But how about Primitive<float>? It seems like a problem, because floats don't have a %= operator. But actually, it isn't, since I'll never call operator %= on Primitive<float>. That's one of the deliberate features of templates. If, for some reason, I would define operator %= as virtual. Or, if i'll pre-export Primitive<float> from a dll to avoid link errors, the compiler will complain even if I never call operator %= on a Primitive<float>. If it would just have fill in a dummy value for operator %= in Primitive<float>'s vtable (that raises an exception?), everything would have been fine.

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• how to interleaving lists

  - by user2829177

  I have two lists that could be not equal in lengths and I want to be able to interleave them. I want to be able to append the extra values in the longer list at the end of my interleaved list.I have this: a=xs b=ys minlength=[len(a),len(b)] extralist= list() interleave= list() for i in range((minval(minlength))): pair=a[i],b[i] interleave.append(pair) flat=flatten(interleave) c=a+b if len(b)>len(a): remainder=len(c)-len(a) for j in range(-remainder): extra=remainder[j] extralist.append(extra) if len(a)>len(b): remainder=len(c)-len(b) for j in range(-remainder): extra=remainder[j] final=flat+extralist return final but if I test it: >>> interleave([1,2,3], ["hi", "bye",True, False, 33]) [1, 'hi', 2, 'bye', 3, True] >>> The False and 33 don't appear. What is it that Im doing wrong?

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• Javascript function programming — receiving elaborate parameters

  - by Barney

  I'm writing a Javascript function that would manipulate an array written on-the-fly and sent as a parameter. The function is written as follows: function returnJourney(animation,clean){ var properties = {}; // loads of other inane stuff for(i in animation[0]) properties[animation[0][i]] = animation[0].i; // heaps more inane stuff } The animation in question is a set of parameters for a jQuery animation. Typically it takes the format of ({key:value,key:value},speedAsInteger,modifierAsString). So to kick off initial debugging I call it with: returnJouney(({'foo':'bar'},3000),1); And straight off the bat things are way off. As far as I see it this would have returnJourney acknowledge clean === 1, and animation being an array with an object as its first child and the number 3000 as its second. Firebug tells me animation evaluates as the number 3000. What am I doing wrong?

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• Can I execute a "variable statements" within a function and without defines.

  - by René Nyffenegger

  I am facing a problem that I cannot see how it is solvable without #defines or incuring a performance impact although I am sure that someone can point me to a solution. I have an algorithm that sort of produces a (large) series of values. For simplicity's sake, in the following I pretend it's a for loop in a for loop, although in my code it's more complex than that. In the core of the loop I need to do calculations with the values being produced. Although the algorithm for the values stays the same, the calculations vary. So basically, what I have is: void normal() { // "Algorithm" producing numbers (x and y): for (int x=0 ; x<1000 ; x++) { for (int y=0 ; y<1000 ; y++) { // Calculation with numbers being produced: if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } // end of calculation }} } So, the only part I need to change is if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } So, in order to solve that, I could construct an abstract base class: class inner_0 { public: virtual void call(int x, int y) = 0; }; and derive a "callable" class from it: class inner : public inner_0 { public: virtual void call(int x, int y) { if ( x+y == 800 && y > 790) { std::cout << x << ", " << y << std::endl; } } }; I can then pass an instance of the class to the "algorithm" like so: void O(inner i) { for (int x=0 ; x<1000 ; x++) { for (int y=0 ; y<1000 ; y++) { i.call(x,y); }} } // somewhere else.... inner I; O(I); In my case, I incur a performance hit because there is an indirect call via virtual function table. So I was thinking about a way around it. It's possible with two #defines: #define OUTER \ for (int x=0 ; x<1000 ; x++) { \ for (int y=0 ; y<1000 ; y++) { \ INNER \ }} // later... #define INNER \ if (x + y == 800 && y > 790) \ std::cout << x << ", " << y << std::endl; OUTER While this certainly works, I am not 100% happy with it because I don't necessarly like #defines. So, my question: is there a better way for what I want to achieve?

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• What are parts of a PHP function named?

  - by MikeG

  I am having trouble figuring out a problem and it is because I don't know the correct terms to be searching for. Could someone please name all the parts of a PHP function and if I'm missing something please add it. function my_function( non_variable $variable_one, $variable_two = "", $variable_three ) { /* inside stuff (Statement?) */ } The answer I'm looking for would look something like this function: declaration my_function: name non_variable: Please Answer $variable_one: variable filled with non_variable The one I really need to know about are non_variable and $variable_one, Thanks! EDIT: more detail about the function function my_function(custom_name $company) { $website = $company->company_website; /* Additional stuff */ }

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• How to call virtual function of an object in C++

  - by SoonDead

  I'm struggling with calling a virtual function in C++. I'm not experienced in C++, I mainly use C# and Java so I might have some delusions, but bear with me. I have to write a program where I have to avoid dynamic memory allocation if possible. I have made a class called List: template <class T> class List { public: T items[maxListLength]; int length; List() { length = 0; } T get(int i) const { if (i >= 0 && i < length) { return items[i]; } else { throw "Out of range!"; } }; // set the value of an already existing element void set(int i, T p) { if (i >= 0 && i < length) { items[i] = p; } else { throw "Out of range!"; } } // returns the index of the element int add(T p) { if (length >= maxListLength) { throw "Too many points!"; } items[length] = p; return length++; } // removes and returns the last element; T pop() { if (length > 0) { return items[--length]; } else { throw "There is no element to remove!"; } } }; It just makes an array of the given type, and manages the length of it. There is no need for dynamic memory allocation, I can just write: List<Object> objects; MyObject obj; objects.add(obj); MyObject inherits form Object. Object has a virtual function which is supposed to be overridden in MyObject: struct Object { virtual float method(const Input& input) { return 0.0f; } }; struct MyObject: public Object { virtual float method(const Input& input) { return 1.0f; } }; I get the elements as: objects.get(0).method(asdf); The problem is that even though the first element is a MyObject, the Object's method function is called. I'm guessing there is something wrong with storing the object in an array of Objects without dynamically allocating memory for the MyObject, but I'm not sure. Is there a way to call MyObject's method function? How? It's supposed to be a heterogeneous collection btw, so that's why the inheritance is there in the first place. If there is no way to call the MyObject's method function, then how should I make my list in the first place?

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• How do you return a string from a function correctly in Dynamic C?

  - by aquanar

  I have a program I am trying to debug, but Dynamic C apparently treats strings differently than normal C does (well, character arrays, anyway). I have a function that I made to make an 8 character long (well, 10 to include the \0 ) string of 0s and 1s to show me the contents of an 8-bit char variable. (IE, I give it the number 13, it returns the string "0001101\0" ) When I use the code below, it prints out !{happy face] 6 times (well, the second one is the happy face alone for some reason), each return comes back as 0xDEAE or "!\x02. I thought it would dereference it and return the appropriate string, but it appears to just be sending the pointer and attempting to parse it. This may seem silly, but my experience was actually in C++ and Java, so going back to C brings up a few issues that were dealt with in later programming languages that I'm not entirely sure how to deal with (like the lack of string variables). How could I fix this code, or how would be a better way to do what I am trying to do (I thought maybe sending in a pointer to a character array and working on it from the function might work, but I thought I should ask to see if maybe I'm just trying to reinvent the wheel). Currently I have it set up like this: this is an excerpt from the main() display[0] = '\0'; for(i=0;i<6;i++) { sprintf(s, "%s ", *char_to_bits(buffer[i])); strcat(display, s); } DispStr(8,5, display); and this is the offending function: char *char_to_bits(char x) { char bits[16]; strcpy(bits,"00000000\0"); if (x & 0x01) bits[7]='1'; if (x & 0x02) bits[6]='1'; if (x & 0x04) bits[5]='1'; if (x & 0x08) bits[4]='1'; if (x & 0x10) bits[3]='1'; if (x & 0x20) bits[2]='1'; if (x & 0x40) bits[1]='1'; if (x & 0x80) bits[0]='1'; return bits; } and just for the sake of completion, the other function is used to output to the stdio window at a specific location: void DispStr(int x, int y, char *s) { x += 0x20; y += 0x20; printf ("\x1B=%c%c%s", x, y, s); }

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• Making a function for selecting from MySQL, how is mine?

  - by Doug

  This is my first time. I will appreciate any thoughts, tips, and what not. How can I improve this? Ultimately, I don't want so many selects in my script. function mysqlSelectCodes($table, $where, $order, $limit) { $sql = "SELECT * FROM $table WHERE $where ORDER BY $order LIMIT $limit" or die(mysql_error()); }

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• Is there any way a program can crash before main()?

  - by Thi

  Is there any way a program can crash before main()?

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• C++ header file and function declaration ending in "= 0"

  - by Adam

  hi, I have the following code inside the .h file and I'm not sure what does the assignment statement do and how is it called properly? virtual void yield() = 0; I thought that the function returns a value of 0 by default but since this function returns void I am a little bit confused. Can anyone comment on this and maybe say how can I refer to this assignment, I mean how is it called in C++ jargon? Thanks.

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• Question on Virtual Methods

  - by bobber205

  IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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• Is it possible to have a variadic function in C with no non-variadic parameter?

  - by Tim

  I have the following function: void doStuff(int unusedParameter, ...) { va_list params; va_start(params, unusedParameter); /* ... */ va_end(params); } As part of a refactor, I'd like to remove the unused parameter without otherwise changing the implementation of the function. As far as I can tell, it's impossible to use va_start when you don't have a last non-variadic parameter to refer to. Is there any way around this? Background: It is in fact a C++ program, so I could use some operator-overloading magic as suggested here, but I was hoping not to have to change the interface at this point. The existing function does its work by requiring that the variable argument list be null-terminated, and scanning for the NULL, therefore it doesn't need a leading argument to tell it how many arguments it has.

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