PS: the proposal of my previous message would also fix this (taken from the data decl of Exp) | InfixE (Maybe Exp) Exp (Maybe Exp) -- {x + y} or {(x+)} or {(+ x)} or {(+)} -- It's a bit gruesome to use an Exp as the -- operator, but how else can we distinguish -- constructors from non-constructors? -- Maybe there should be a var-or-con type? -- Or maybe we should leave it to the String itself? Now the operator can be just a Name. I'm even keener. Simon