The REPL as such is on its base a relatively primitive thing: it reads an expression from a stream, evaluates the expression, while doing that it prints any sid

The REPL as such is on its base a relatively primitive thing: it reads an expression from a stream, evaluates the expression, while doing that it prints any side effects and then prints the result. On top of that one can image various user interfaces. * sophisticated text based repls with integrated repl debuggers and things like structure editors: example Interlisp. * graphical REPLs which use a graphics capable stream * presentation-based REPLs like the one from Symbolics Dynamic Windows or CLIM (the Common Lisp interface manager) * rich structure browser REPLs like the one from Apply Dylan * REPLs inside a text editor UI * REPLs inside an IDE Then there is also the Notebook user interface, which was mostly developed around interactive mathematics software with visualization features. Mathematica made it popular (there were a few earlier systems with similar ideas). It adds a notebook-based graphical user interface with 2d and 3d graphics. It also usually makes it kind of persistent -> one can store and reopen saved Notebooks. No wonder that it is popular in areas where data visualization and maths is important. I haven't seen it used outside of that area that much, though.