Monadic Functional Reactive Programming Atze van der Ploeg Centrum Wiskunde & Informatica
[email protected] Abstract FRP is based on the notion of a reactive computation: a monadic Functional Reactive Programming (FRP) is a way to program reac- computation which may require the occurrence of external events tive systems in functional style, eliminating many of the problems to continue. The Monadic FRP variant of a signal is a signal that arise from imperative techniques. In this paper, we present an computation: a reactive computation that may also emit values alternative FRP formulation that is based on the notion of a reac- during the computation. tive computation: a monadic computation which may require the This novel formulation has two differences with other FRP occurrence of external events to continue. A signal computation approaches: is a reactive computation that may also emit values. In contrast to • In contrast to signals in other FRP formulations, signal compu- signals in other FRP formulations, signal computations can end, tations can end. This leads to a simple, monadic interface for leading to a monadic interface for sequencing behavioral changes. sequencing behavioral changes. This interface has several advantages: routing is implicit, sequencing • behaviors is easier and more intuitive than the switching combina- In other FRP approaches, either the entire FRP expression is tors found in other FRP approaches, and dynamic lists require much re-evaluated on each external stimulus, or impure techniques less boilerplate code. In other FRP approaches, either the entire are used to prevent redundant re-computations: re-computing FRP expression is re-evaluated on each external stimulus, or impure the current value of signal while the input it depends on has not techniques are used to prevent redundant re-computations.