Python Lambda Experiment

This is "pyle", an interpreter for s-expressions and lambda functions written in Python.

Copyright (C) 2017, 2018 Juergen Nickelsen ni@w21.org. See LICENSE for the conditions under which this code is licensed to you.

Pyle is meant to be a rather (although not strictly) minimal interpreter, with few features in the builtin core. More functionality shall, if possible, be implemented in the language itself. In order to do that, it has macros.

The supported data types are symbols, strings, numbers, pairs, and errors. Variable numbers of arguments to functions are implemented using improper argument lists like in Scheme. This, together with the traditional defun syntax, means, consequently, that a function of zero or more arguments will not have a parameter list, but rather a parameter symbol, like this:

  (defun adder args
    (apply '+ args))

I admit this is more elegant in Scheme with (define (adder . args) ...)

Update 2018-09: Like similar interpreters before, I wrote Pyle to learn more about its implementation language. I started it short after starting to learn Python at all, and working on Pyle helped me with that.

In between, as I have gained more experience with Python in other projects, I would certainly do quite a few things in Pyle differently now, e.g. register the builtin functions using a decorator, and make the Object hierarchy somewhat less messy. I don't know if I'll ever get around to doing that, but there are certainly quite a few places where I could do things more elegant and more pythonic.