OCaml First-Class Modules: Runtime Overhead and Type Identity

OCaml's module system provides a mechanism for strong encapsulation through signatures and structures. While static module instantiation is the standard for type-safe abstraction, first-class modules allow modules to be treated as values, enabling dynamic selection of implementations at runtime.

There is a design trade-off between the flexibility of first-class modules and the performance characteristics of static modules. Specifically, the transition from a static module to a first-class module may introduce runtime overhead and impact how the compiler handles type identity across abstraction boundaries.

• What is the specific performance cost associated with invoking functions within a first-class module compared to a statically instantiated module?
• How does the use of first-class modules affect the compiler's ability to optimize type identity when modules are passed as values?