| > and is it (still?) true that GHC never expands them? | | I'm not sure if GHC guarantees never to duplicate a redex, Simon PJ | might know. Yes, it's very careful not to duplicate a redex, except for ones of known bounded size, like x +# y, where sharing the work costs more than duplicating int. But I'd advise against relying on this guarantee, because it's a pragmatic one rather than a semantic one. Simon