REPL

Run rontolisp with no file argument to start an interactive read-eval-print loop. It reads one expression at a time, evaluates it on the tree-walking interpreter, and prints the result -- the quickest way to explore the language.

rontolisp

CL-USER> (+ 1 2)
3
CL-USER> (* 3 (+ 4 5))
27
CL-USER> (defun fact (n) (if (= n 0) 1 (* n (fact (- n 1)))))
FACT
CL-USER> (fact 10)
3628800
CL-USER> (quit)

Each top-level form is evaluated as soon as it is complete, and its value is echoed back. Definitions persist across inputs: a defun, defvar, or setq entered at one prompt is visible at every later one, so you can build up state incrementally within a session.

The prompt is the name of the current package, the way CL-USER> names it in any Common Lisp REPL. It is read again before every line, so an (in-package ...) typed at one prompt shows at the next -- which package a bare symbol is read into is never left invisible:

CL-USER> (defpackage :app (:use :cl))
APP
CL-USER> (in-package :app)
:APP
APP> (defun greet () "hi")
APP::GREET
APP> (in-package :cl-user)
:CL-USER
CL-USER> (app::greet)
"hi"

A form that returns multiple values echoes every value, one per line -- the quotient and the remainder of floor, the value and the present-p flag of gethash. (values) returns no value at all and echoes nothing:

CL-USER> (floor 10 3)
3
1
CL-USER> (gethash 'b (make-hash-table))
NIL
NIL
CL-USER> (values 1 2 3)
1
2
3
CL-USER> (values)
CL-USER>

The prompt accepts multi-line input -- if an expression has unbalanced parentheses, the REPL keeps reading until it is closed before evaluating. It also supports line editing, history navigation with the up/down arrow keys, and Ctrl-C to cancel the current input. Type (quit) or press Ctrl-D to exit.

Try a quick expression here: