The void type, in several programming languages derived from C and Algol68, is the type for the result of a function that returns normally, but does not provide a result value to its caller. Usually such functions are called for their side effects, such as performing some task or writing to their output parameters. The usage of the void type in such context is comparable to that of the syntactic constructs which define subroutines in Visual Basic and procedures in Pascal. It is also similar to the unit type used in functional programming languages and type theory; however, there are some differences in allowable usage, in that the void type is taken to be an empty type with no values. See Unit type#In programming languages for a comparison.