Psil - Python S-expression Intermediate Language

Greg Hewgill
http://hewgill.com

Psil is a Lisp family language designed for close integration with Python.

Requirements

Psil requires Python 3.1 or later.

Usage

To run a REPL (interactive read-eval-print-loop):

$ python3.1 psil.py
PSIL interactive mode
Use (quit) to exit
> 

To run a Psil script in a file:

$ python3.1 psil.py hello.psil
hello world

or (on Unix-like systems):

$ ./hello.psil
hello world

To run Psil code from within Python:

#!/usr/bin/env python3.1

from psil.interpreter import psil

square = psil("""
    (lambda (x)
        (* x x))
""")

print(square(5))

A slightly more advanced example where the glob=globals() is needed so that the Psil code can see back into the Python module for the fact function:

#!/usr/bin/env python3.1

from psil.interpreter import psil

fact = psil("""
    (lambda (x)
      (if (== x 0)
          1
          (* x (fact (- x 1)))))
""", glob=globals())

print(fact(5))

The psil.test file is a doctest module with many examples including macros. To run the tests:

$ python3.1 psil.py --test