Functional languages such as Standard ML, Scheme and Scala do not restrict side effects, but it is customary for programmers to avoid them. The functional language Haskell eliminates side effects such as I/O and other stateful computations by replacing them with monadic actions. The lack of side effects makes it easier to do formal verification of a program. By contrast, declarative programming is commonly used to report on the state of system, without side effects.įunctional programming aims to minimize or eliminate side effects.
SIDE EFFECT SYNONYM UPDATE
For example, imperative programming is commonly used to produce side effects, to update a system's state. The degree to which side effects are used depends on the programming paradigm. Side effects play an important role in the design and analysis of programming languages. Understanding and debugging a function with side effects requires knowledge about the context and its possible histories. In the presence of side effects, a program's behaviour may depend on history that is, the order of evaluation matters. Example side effects include modifying a non-local variable, modifying a static local variable, modifying a mutable argument passed by reference, performing I/O or calling other functions with side-effects. In computer science, an operation, function or expression is said to have a side effect if it modifies some state variable value(s) outside its local environment, which is to say if it has any observable effect other than its primary effect of returning a value to the invoker of the operation. For similar uses, see hidden variable (disambiguation).
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