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In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens.This means the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures. [1]
Call by reference (or pass by reference) is an evaluation strategy where a parameter is bound to an implicit reference to the variable used as argument, rather than a copy of its value. This typically means that the function can modify (i.e., assign to) the variable used as argument—something that will be seen by its caller. Call by reference ...
Replace each free variable with an additional argument to the enclosing function, and pass that argument to every use of the function. Replace every local function definition that has no free variables with an identical global function. Repeat steps 2 and 3 until all free variables and local functions are eliminated.
In a given programming language design, a first-class citizen [a] is an entity which supports all the operations generally available to other entities. These operations typically include being passed as an argument, returned from a function, and assigned to a variable. [1]
Calling f with a regular function argument first applies this function to the value 2, then returns 3. However, when f is passed to call/cc (as in the last line of the example), applying the parameter (the continuation) to 2 forces execution of the program to jump to the point where call/cc was called, and causes call/cc to return the value 2.
In the lambda calculus, which only uses functions of a single variable, this can be done via the Y combinator. First make the higher-order function of two variables be a function of a single variable, which directly returns a function, by currying:
In an object-oriented programming language such as Java versions before function-valued arguments, the behavior of a callback can be achieved by passing an object that implements an interface. The methods of this object are callbacks.
This property is inherited from lambda calculus, where multi-argument functions are usually represented in curried form. Currying is related to, but not the same as partial application . [ 1 ] [ 2 ] In practice, the programming technique of closures can be used to perform partial application and a kind of currying, by hiding arguments in an ...