Feature Request: Control Structures

Is it possible to implement simple control structures to repeat a macro or a block inside a macro (or even a macro calling another macro) n-times or until end-of-line or end-of-file, for example?

The issue names no files, tests, syntax, or execution entry point. Begin by surveying the repository to find how macros and blocks are represented and executed. Before implementation, agree on syntax and termination semantics; done would require defined behavior and tests for repetition, end-of-line or end-of-file stopping, and nested macro calls.

Written by the indexing model from the issue text.