Exploratory programming
Exploratory programming is an important part of the software engineering cycle: when a domain is not very well understood or open-ended, or it's not clear what algorithms and data structures might be needed for an implementation, it's useful to be able to interactively develop and debug a program without having to go through the usual constraints of the edit-compile-run-debug cycle. Many languages provide support for exploratory programming via interactivity, dynamicity, and extensibility, such as Lisp, Smalltalk, Self, Obliq, Cecil, Dylan, and Python.