Principal Signatures for Higher-Order Program Modules

Abstract

Under the Damas-Milner type discipline for functional languages, every expression has principal type, if it elaborates at all. In the type discipline for ML Modules, a signature expression has a principal signature, if it elaborates at all. However, while functions can be higher-order in ML, parameterised modules in ML are first-order only. We present a type discipline for a skeletal higher-order module language which has principal signatures. Sharing and multiple views of structures are handled in a manner which is compatible with the semantics of the first-order ML modules.