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: If your using Apple's version of C then you can use their new block syntax which adds closures and runtime blocks to the C language. Apple has submitted their change to the C language to be added to the standard (its currently implemented on the the llvm-gcc and clang C compilers. These blocks/closures work in C, C++ and Objective-C
: Here is an example of what they look like in C:
<syntaxhighlight lang="C">
void EvalFuncOnGrid( float(^block)(float) ) {
int i;
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Caller();
}
</syntaxhighlight>
: These blocks can be treated as first class functions, they have a dynamic binding, can be passed around at run time and automatically track references to variables used inside that are declared outside of their scope, thus they act as true closures. The complete specification can be found here: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1370.pdf
: [[Special:Contributions/75.143.82.88|75.143.82.88]] ([[User talk:75.143.82.88|talk]]) 03:29, 3 August 2009 (UTC)
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So this is a classic "proof" of first class functions in php:
<syntaxhighlight lang="php">
function makeDerivative($fn, $deltaX) {
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echo $cos(pi() / 2); // 0
</syntaxhighlight>
But there are a few things wrong with it. First, this code actually throws a catchable fatal error. The label 'sin' doesn't refer to the builtin function but rather the constant sin. Since such a constant wasn't defined, php pretends you meant string 'sin'. What you should actually do is:
<syntaxhighlight lang="text">
$cos = makeDerivative('sin', 0.00000001);
</syntaxhighlight>
and for all intents and purposes, $fn in the closure is a string. When you use $fn($x), php resolves the value of the string to some function and calls it with the arguments $x, but in no situation can you actually store or pass in a reference to a function. The closure object is actually first class (you can pass it around, assign it to variables), but functions are not. [[Special:Contributions/72.235.55.215|72.235.55.215]] ([[User talk:72.235.55.215|talk]]) 09:36, 15 June 2012 (UTC)
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It seems to me that if you have to wrap a function in a 'proc' object in order to assign it to a variable, then your functions are second-class citizens. Something else I would expect to be able to do in a language that supports first class functions:
<syntaxhighlight lang="text">
def f(x)
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g(2)
</syntaxhighlight>
This doesn't work in ruby either. You can't assign a function using = (the normal assignment operator), you have to use def, or wrap the function in an object. That's not first-class.[[User:88.96.214.6|88.96.214.6]] 12:26, 20 March 2007 (UTC)
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:: However you can access them by calling their containing module and asking for the function. Like:
<syntaxhighlight lang="text">
def f(x) # global functions are contained in the Kernel
x + 4
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g.class #=> 'Method'
proc = g.to_proc # returns the method as a Proc
</syntaxhighlight>
:: Also, in Ruby, a Proc is by definition exactly what a first class function is. Granted, you can't directly assign a method to a variable using the = operator like in other languages, I would still argue that Ruby does indeed have first class functions.
:: [[Special:Contributions/75.143.82.88|75.143.82.88]] ([[User talk:75.143.82.88|talk]]) 03:07, 3 August 2009 (UTC)
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I disagree with various statements concerning whether or not this is generally available in C - or that it must somehow require specific hardware. Consider the following:
<syntaxhighlight lang="text">
// imports first_class dll.
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}
</syntaxhighlight>
Windows actually has a "LoadModule" function (I think) that allows you to load dlls when you want them or need them, allowing you to do things like have one version of a program that can use different DLL's according to different OS, or whatever. These can then be loaded during execution rather then when the program first starts up (automatically) and thus avoiding the dreaded "required DLL not found error". The process can even be applied recursively, so that DLL's which have various complicated and interacting dependencies can be linked in and out, etc. In my simple example I am suggesting a kind of persistent data block type (which could also be modified if needed by using placement new, casting to a void pointer, and/or realloc as needed).
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