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Various techniques for returning multiple values include: Returning a tuple of values. This is conventional in languages (such as Python) that have a built-in tuple data type and special syntax for handling these: in Python, x, y = f() calls the function f returning a pair of values and assigns the elements of the pair to two variables ...
I/O is inherently impure: input operations undermine referential transparency, and output operations create side effects.Nevertheless, there is a sense in which a function can perform input or output and still be pure, if the sequence of operations on the relevant I/O devices is modeled explicitly as both an argument and a result, and I/O operations are taken to fail when the input sequence ...
By returning a null object (i.e., an empty list) instead, there is no need to verify that the return value is in fact a list. The calling function may simply iterate the list as normal, effectively doing nothing. It is, however, still possible to check whether the return value is a null object (an empty list) and react differently if desired.
In an interactive log-file browser, the right thing to do might be to return the entry unparsed, so the user can see it—but in an automated log-summarizing program, the right thing to do might be to supply null values for the unreadable fields, but abort with an error, if too many entries have been malformed.
In functional programming, a monad is a structure that combines program fragments and wraps their return values in a type with additional computation. In addition to defining a wrapping monadic type, monads define two operators: one to wrap a value in the monad type, and another to compose together functions that output values of the monad type (these are known as monadic functions).
The return value from a function is provided within the function by making an assignment to an identifier with the same name as the function. [5] However, some versions of Pascal provide a special function Exit(exp); that can be used to return a value immediately from a function, or, without parameters, to return immediately from a procedure. [6]
In methods that have a return value of type Task<T>, methods declared with async must have a return statement of type assignable to T instead of Task<T>; the compiler wraps the value in the Task<T> generic. It is also possible to await methods that have a return type of Task or Task<T> that are declared without async.
function factorial (n is a non-negative integer) if n is 0 then return 1 [by the convention that 0! = 1] else if n is in lookup-table then return lookup-table-value-for-n else let x = factorial(n – 1) times n [recursively invoke factorial with the parameter 1 less than n] store x in lookup-table in the n th slot [remember the result of n! for ...