Warning: This is the manual of the legacy Guile 2.0 series. You may want to read the manual of the current stable series instead.

6.13.5 Prompts

Prompts are control-flow barriers between different parts of a program. In the same way that a user sees a shell prompt (e.g., the Bash prompt) as a barrier between the operating system and her programs, Scheme prompts allow the Scheme programmer to treat parts of programs as if they were running in different operating systems.

We use this roundabout explanation because, unless you’re a functional programming junkie, you probably haven’t heard the term, “delimited, composable continuation”. That’s OK; it’s a relatively recent topic, but a very useful one to know about.