Quoting Jesper Louis Andersen <jlouis@mongers.org>: > datatype ('a, 'b) either = INL of 'a > | INR of 'b I like this one. Now that I think about it, I recall seeing this naming used somewhere (article or book). The "IN" part also nicely suggests the antonym for the occasionally useful partial destructors: fun outL (INL x) = x fun outR (INR x) = x -Vesa Karvonen