This is an interpreter for a really simple dynamically scoped Scheme dialect. It only runs with Gforth, because it uses Gforth's structs to implement its data structures. One of the more involved parts of this interpreter is the reader, where I had to do quite a lot of stack juggling to keep everything in line. It doesn't look very involved now but I remember spending quite some time thinking about the stack layout for the reader routines. Read here why the way I did it is most certainly wrong.

Assuming you have Gforth installed (if you're on MacOS you can get it via Brew), start it with

gforth lisp.fs

There are mainly three words of interest:

• lisp-load-from-string reads and evaluates a string.

• lisp-load-from-file reads and evaluates a file, given a filename.

• lisp-display prints a lisp value.

Example:

s" (+ 1 2 3)" lisp-load-from-string lisp-display
=> 6 ok
s" test.scm" lisp-load-from-file lisp-display
=> 4 120 () ok

In this example, 4 and 120 are printed in test.scm, and () is the result of the evaluation of the file.