This is an interpreter for a sub-set of the Scheme programming language. It was written as a learning exercise, and should not be used for anything important.

To use the interpreter, write your Scheme code into a text file and run scheme.py, passing the file name and location as a command-line argument, for example:

python scheme.py mycode.txt

The interpreter supports basic arithmetic and equality operators, conditional statements, the cons/car/cdr list operations, define and lambda.

Each statement in the source file will be evaluated in turn, and any printable results will be displayed to standard output. A few working Scheme programs and their resulting output are shown below:

(define factorial (
lambda (n) (
if (= n 1) 1 (* n (factorial (- n 1)))
)
)
)
(factorial 6)

720.0

(define fib (
lambda (n) (
if (< n 3)
1
(+ (fib (- n 1)) (fib (- n 2)))
)
)
)
(fib 10)

55.0

(define ackermann (
lambda (m n) (
if (= m 0)
(+ n 1)
(if (= n 0)
(ackermann (- m 1) 1)
(ackermann (- m 1) (ackermann m (- n 1))))
)
)
)
(ackermann 3 3)

61.0