Effects. A polymorphic language based on Scheme, allowing side effects and first-class functions. It attempts to integrate functional and imperative programming. Expressions have types, side effects (e.g. reading, writing or allocating) and regions (stating where the effects may occur).

Versions: FX-89, FX-90.

["The FX-87 Reference Manual", D.K. Gifford <[email protected]> et al, MIT/LCS/TR-407, Oct 1987].