"
Read-
EVAL-
Print-
Loop" - the part of any
Lisp (including
Scheme!) known colloquially as "the
interpreter".
Given the rest of the language, the (interactive) interpreter just LOOPs: it READs a sexp, EVALs it, and PRINTs the result.
Edit: Other languages that incorporate a REPL include Python, Haskell and R. Other languages have REPL available through third-party tools. -w