This paper presents a scheme comprising a type system and a type-directed compilation method that enables users to integrate high-level key-value store (KVS) operations into statically typed polymorphic functional languages such as Standard ML. KVS has become an important building block for cloud applications because of its scalability. The proposed scheme will enhance the productivity and program safety of KVS by eliminating the need for low-level string manipulation. A prototype that demonstrates its feasibility has been implemented in the SML# language and clarifies issues that need to be resolved in further development towards better practical performance.