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 S.mit.edu> et al, MIT/LCS/TR-407, Oct 1987]. (1995-01-31)