At the moment HsExpr includes the following two constructors | ExprWithTySig (LHsExpr id) (LHsSigWcType id) | ExprWithTySigOut -- Post typechecking (LHsExpr id) (LHsSigWcType Name) -- Retain the signature, -- as HsSigType Name, for -- round-tripping purposes I do not understand why we need the second one, which hard-codes Name instead of id. There are a couple of places where there is an XXXOut variant with hard coded Name parameter, and these complicate creating any kind of custom class intended to work on a parameterised AST as it ripples out and forces Name instances of it everywhere. Perhaps we should introduce HsExprLR id id to cope with renaming? Alan