A Little Scheme in Common Lisp

This is a small interpreter of a subset of Scheme. It runs on CLISP 2.49, SBCL 2.0.3, ECL 16.1.3, GCL 2.6.12 and ABCL 1.6.0. It implements almost the same language as

and their meta-circular interpreter, little-scheme.

As a Scheme implementation, it optimizes tail calls and handles first-class continuations properly.

How to run

$ sbcl --script scm.l
> (+ 5 6)
11
> (cons 'a (cons 'b 'c))
(A B . C)
> (list
1
2
3)
(1 2 3)
>

Press EOF (e.g. Control-D) to exit the session.

> Goodbye
$

You can run it with a Scheme script. Examples are found in little-scheme; download it at .. and you can try the following:

$ sbcl --script scm.l ../little-scheme/examples/yin-yang-puzzle.scm | head

*
**
***
****
*****
******
*******
********
*********
$ sbcl --script scm.l ../little-scheme/examples/amb.scm
((1 A) (1 B) (1 C) (2 A) (2 B) (2 C) (3 A) (3 B) (3 C))
$ sbcl --script scm.l ../little-scheme/examples/nqueens.scm
((5 3 1 6 4 2) (4 1 5 2 6 3) (3 6 2 5 1 4) (2 4 6 1 3 5))

Put a "-" after the script in the command line to begin a session after running the script.

$ sbcl --script scm.l ../little-scheme/examples/fib90.scm -
2880067194370816120
> (globals)
(GLOBALS ERROR NUMBER? = < * - + APPLY CALL/CC SYMBOL? EOF-OBJECT? READ
           NEWLINE DISPLAY LIST NOT NULL? PAIR? EQ? CONS CDR CAR FIBONACCI)
> (fibonacci 16)
987
> (fibonacci 1000)
43466557686937456435688527675040625802564660517371780402481729089536555417949051
89040387984007925516929592259308032263477520968962323987332247116164299644090653
3187938298969649928516003704476137795166849228875
>

The implemented language

Expression types

v [variable reference]
(e0 e1...) [procedure call]
(quote e)
'e [transformed into (quote e) when read]
(if e1 e2 e3)
(if e1 e2)
(begin e...)
(lambda (v...) e...)
(set! v e)
(define v e)

For simplicity, this Scheme treats (define v e) as an expression type.

Built-in procedures


(`car` lst)	(`display` x)	(`+` n1 n2)
(`cdr` lst)	(`newline`)	(`-` n1 n2)
(`cons` x y)	(`read`)	(`*` n1 n2)
(`eq?` x y)	(`eof-object?` x)	(`<` n1 n2)
(`pair?` x)	(`symbol?` x)	(`=` n1 n2)
(`null?` x)	(`call/cc` fun)	(`number?` x)
(`not` x)	(`apply` fun arg)	(`globals`)
(`list` x ...)	(`error` reason arg)

(error reason arg) signals an error with the message "Error: reason: arg". It is based on SRFI-23.
(globals) returns a list of keys of the global environment. It is not in the standard.

Caveat

It does not print #t nor #f properly yet.