As a point of historical note, Haskell has not had encapsulated effects from the start. Monadic IO was introduced in version 1.3, roughly 6 years after version

As a point of historical note, Haskell has not had encapsulated effects from the start. Monadic IO was introduced in version 1.3, roughly 6 years after version 1.0. http://research.microsoft.com/en-us/um/people/simonpj/papers/history-of-haskell/history.pdf http://research.microsoft.com/en-us/um/people/simonpj/papers...