Haskell Ports Library provides ports in Haskell.
Ports are an abstraction for modelling variables
whose values evolve over time without the need to
resort to mutable variable, such as
IORefs. More precisely, a port represents all
values that a time-dependent variable successively
take as a stream, where each element of the stream
corresponds to a state change. A port supports
concurrent construction of the time series, or
stream of values. Ports are ideally suited for
purely functional GUI interfaces that completely
avoid the use of mutable variables.
