The Rakudo REPL’s prompt consists of a result number in square brackets followed by a space character, a closing angle bracket, and another space character. Currently, there is no way to customize this prompt at runtime.

So, if, e.g., you are testing code examples in the REPL and then want to put the code and results into your notebook or share them with others, but without the result count included (because it doesn’t serve any meaningful purpose in your use case), you will have do extra work to remove it.

There are probably a couple of other good reasons to have a run-time configurable prompt, e. g., adding other bits of information or color to it in order to distinguish between several REPLs running in parallel.