We address the problem of writing compilers targeting
complex execution environments
, such as computer clusters composed of machines with multi-core CPUs. To that end we introduce
. These compilers can pass sub-programs to several child (partial) compilers, combining the code generated by their children to generate the final target code. We define a set of high-level polymorphic operations manipulating both compilers and partial compilers as first-class values. These mechanisms provide a software architecture for modular compiler construction. This allows the building of a forest of compilers, providing a structured treatment of multistage compilers.