StaticTyping of the (side)effects of a method.

Java's CheckedException is an example of an explicit effect type.

Chapter 3 of "Advanced Topics in Types and Programming Languages" ''Benjamin C. Pierce'' has a nice formal introduction with application to Regions. Available on Google here:

  http://books.google.de/books?hl=de&lr=&id=A5ic1MPTvVsC&oi=fnd&pg=PA87&dq=effect-typing+method&ots=PmoEkJcy5w&sig=QylSEShgA4jypQ6jnNEOdZNP_dQ

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Related to OnMonads (monads and effect types seem to be dual or at least strongly connected)