-- | Those variables free in the both the left right hand sides of a rule
-- returned as FV computation
ruleFVs :: CoreRule -> FV
ruleFVs (BuiltinRule {}) = emptyFV
ruleFVs :: CoreRule -> FV
ruleFVs (BuiltinRule {}) = emptyFV
ruleFVs (BuiltinRule {}) = emptyFV