Hi all If I have a happy parser for an AST that is polymorphic, is there any way to put constraints on the individual rules? e.g. if I have data Foo a = Foo String a and a rule something like foo :: { (Show a) => Foo a } foo : otherrule { Foo (show $1) $1 } Because of the way the tables are constructed in happy, the Show constraint is not attached to the point where the rule RHS is applied. Is this simply impossible? Alan