REPL

With no file, --source-language scheme starts a Scheme REPL. Values are echoed as write prints them. A definition echoes nothing, and neither does the unspecified value -- what display, set!, for-each or an if with no branch taken answer, also when a procedure of your own ends in one. A form may span lines. An error, a stack overflow included, is reported and the session goes on with its definitions; (exit) ends it. With input piped in, the session is a script runner, as the Common Lisp REPL is: no prompt, errors on standard error, exit status 1 if any form failed.

$ rontolisp --source-language scheme
scheme> (define (square x) (* x x))
scheme> (map square '(1 2 3))
(1 4 9)
scheme> (set! square -)
scheme> (square 5)
-5
scheme> (list #t #f '() 'Sym)
(#t #f () Sym)
scheme> (define (show x) (display x) (newline))
scheme> (show 'done)
done
scheme> (exit)

Everything those twelve libraries export -- plus the Structure and Interpretation of Computer Programs (SICP)-compatibility names, which no (import ...) names, unless --scheme-standard r7rs -- is visible from the start, and an (import ...) typed at the prompt only adds names. Definitions typed at separate prompts see each other in either order, as they would in one file. Two things differ from a file, because a form is fixed when it is typed: redefining a built-in procedure (square) does not reach the forms typed before it, and a procedure that calls itself in tail position keeps looping on itself if a later set! replaces it while an old copy is still held.