An interpreter for the Turbak and Gifford's language PostFix. PostFix is a stack-based language described in Chapter 1 of the book Design Concepts in Programming Languages.

The interpreter is written in Python 3, with a test suite runnable with py.test. After cloning this repo, run the tests with something like:

python3 -m pytest -s -v tests

You can run the interpreter from the command line. Supply the program as the first argument, with subsequent arguments (if any) comprising the initial stack (starting with the top element):

$ ./postfix '((mul sub) (1 nget mul) 4 nget swap exec swap exec)' -10 2
42

You can also invoke the interpreter from within Python code like so:

from interpreter import run
program = "((mul sub) (1 nget mul) 4 nget swap exec swap exec)"
run(command, -10, 2)
# => 42