We report on a technique for interfacing an untyped logic language to a statically polymorphically typed functional language. Our key insight is that polymorphic types can be interpreted as "need to know" specifications on function arguments. This leads to a criterion for liberally yet safely invoking the functional language to reduce application terms as required during unification in the logic language. This method, called P-unification, enriches the capabilities of each language while retaining the integrity of their individual semantics and implementation technologies. An experimental test has been successfully performed, whereby a Horn clause logic programming (HCLP) interpreter written in Common Lisp was interfaced to the Standard ML of New Jersey system. The latter implementation was employed (i) on untyped or dynamically typed data, even though it is statically typed; (ii) lazily, even though it is strict, and (iii) on alien HCLP terms such as unbound variables --- without the ...