3.26 Importing Modules Lazily: lazy-require
(lazy-require [module-path (fun-import ...)] ...)
fun-import = fun-id | (orig-fun-id fun-id)
If the enclosing relative phase level is not 0, then module-path is also placed in a submodule (with a use of define-runtime-module-path-index at phase level 0 within the submodule). Introduced submodules have the names lazy-require-n-m, where n is a phase-level number and m is a number.
When the use of a lazily-required function triggers module loading, register-external-module declares a potential compilation dependency (in case the function is used in the process of compiling a module).