Dynamic extension of typed functional languages

We present a solution to the problem of dynamic extension in staticallytyped functional languages with type erasure. The presented solutionretains the benefits of static checking, including type safety,aggressive optimizations, and native code compilation of components,while allowing extensibility of programs at runtime.Our approach is based on a framework for dynamic extension in astatically typed setting, combining dynamic linking, runtime typechecking, first class modules and code hot swapping. We show that thisframework is sufficient to allow a broad class of dynamic extensioncapabilities in any statically typed functional language with typeerasure semantics.Uniquely, we employ the full compile-time type system to perform runtimetype checking of dynamic components, and emphasize the use of nativecode extension to ensure that the performance benefits of static typingare retained in a dynamic environment. We also develop the concept offully dynamic software architectures, where the static core isminimal and all code is hot swappable. Benefits of the approach includehot swappable code and sophisticated application extension via embeddeddomain specific languages.We instantiate the concepts of the framework via a full implementationin the Haskell programming language: providing rich mechanisms fordynamic linking, loading, hot swapping, and runtime type checking inHaskell for the first time. We demonstrate the feasibility of thisarchitecture through a number of novel applications: an extensible texteditor; a plugin-based network chat bot; a simulator for polymerchemistry; and xmonad, an extensible window manager. In doing so, wedemonstrate that static typing is no barrier to dynamic extension