callable

Closures on the other hand bind data to functions; so the function is always callable but the data is bound to this instance of the function.

In Java, this typically means subclassing Callable or some other class and you end up with lots of anonymous subclasses, which can be quite verbose.

For example, std::function is able to wrap any callable type without them having to have any base classes.

In a real world program you would validate input and make sure you get something callable (with either technique).

C/C++ is the language you write the library in, so that it's callable from every other language.

Now what would be really cool is the ability to define a filter function in JS callable from the CSS.

That callable will typically be Django's entry point, where Django consults its root urlconf and routes the request to your application code.

I tend to use map if my mapping function is already available to me as a callable.

Truly cross-platform (not just Windows/Linux/Mac) performance-sensitive libraries that need to be callable (using bindings) from a wide range of programming languages (including C).

This has the being callable from other languages, CPython and PyPy.

Or having code that's callable from another GC-ed language like Ruby/Python/etc.

OS work, drivers, common libs like OpenSSL callable from other apps, infrastructure work, etc.

It is a part of the structured programming idea to make modules callable by a "shorthand".

This is splitting "callable things" into two worlds, functions and macros, rather than all values.

I learnt this "map as callable" idea fron clojure and wondered why it is not more common.

I've certainly never heard of it referred to as such in Javascript or Ruby, and most-often referred to as "Callable" in Java.

It wasn't pretty, but Java <=1.7 could still support a functional programming style by using `Callable` objects.

Even then, Java's had ExecutorService, Callable<T> and BlockingQueue<T> for a long time.