Effect, Eff, and Aff

Some History

Before the 0.12.0 release, the Effect monad used to be called Eff.

In short, the decision was made to drop Eff's "extensible effects". Presumably, to prevent code breakage, Eff and package location in imports was unchanged. Rather, it can now be found in the purescript-eff package. Its replacement was called Effect.

(You can read more about the decision making process here. If one is curious about Eff, read through the related section in the "Purescript by Example" book as it won't be covered here.)


The Aff monad was introduced and in use before this decision was made. Thus, history explains the naming behind Aff: if Eff was for synchronous effects, then Aff is for asychronous effects.

Aff will be covered in more depth in the upcoming files.