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In computer programming, an anonymous function (function literal, expression or block) is a function definition that is not bound to an identifier.Anonymous functions are often arguments being passed to higher-order functions or used for constructing the result of a higher-order function that needs to return a function. [1]
sort is a generic function in the C++ Standard Library for doing comparison sorting.The function originated in the Standard Template Library (STL).. The specific sorting algorithm is not mandated by the language standard and may vary across implementations, but the worst-case asymptotic complexity of the function is specified: a call to sort must perform no more than O(N log N) comparisons ...
C++11 and later – via lambda expressions (see quicksort example above) [11] Eiffel – explicitly disallows nesting of routines to keep the language simple; does allow the convention of using a special variable, Result, to denote the result of a (value-returning) function; C# and Visual Basic – via lambda expressions
Of course, this is just a trivial example. To understand what power a functor provides more than a regular function, consider the common use case of sorting objects by a particular field. In the following example, a functor is used to sort a simple employee database by each employee's ID number.
In this example, the lambda expression (lambda (book) (>= (book-sales book) threshold)) appears within the function best-selling-books. When the lambda expression is evaluated, Scheme creates a closure consisting of the code for the lambda expression and a reference to the threshold variable, which is a free variable inside the lambda expression.
Sorting functions, which take a comparison function as a parameter, allowing the programmer to separate the sorting algorithm from the comparisons of the items being sorted. The C standard function qsort is an example of this.
In this manner, function definition expressions of the kind shown above can be thought of as the variable binding operator, analogous to the lambda expressions of lambda calculus. Other binding operators, like the summation sign, can be thought of as higher-order functions applying to a function. So, for example, the expression
The lambda expression being analyzed. The table parameter lists for names. The table of values for parameters. The returned parameter list, which is used internally by the; Abstraction - A lambda expression of the form (.) is analyzed to extract the names of parameters for the function. {-- [(.