Question about scopes / environments

[rcanepa]

First, I want to thank you for this amazing project. Right now, I am working on part 8 and I can tell you that I have learnt and enjoyed the process a lot.

I am not sure if this is the right place to ask for help (I could't find any information about where help question should be asked).

Anyway, I am looking for guidance on how should I approach this situation:

def test_let_bindings_overshadow_outer_environment():
    """
    Let bindings should shadow definitions in from outer environments
    """

    interpret("(define foo 1)", env)

    program = """
        (let ((foo 2))
             foo)
    """

My evaluator function creates a new Environment every time it found a "let" special form, which is created by extending the one its belong to:

def eval_let(ast, env):
    let_env = env.extend({})

    bindings = ast[1]

    print bindings

    args = {}
    for b in bindings:
        key = b[0]
        val = evaluate(b[1], let_env)
        args[key] = val
        let_env.set(key, val)

    print args

    return evaluate(ast[2], let_env)

However, this only work if I allow override already defined variables in my Environment (this way I can use the set method to change the value of a variable), but this doesn't seem to be right way to do it because I can also define multiple times the same variable, which of course is wrong.

How should I implement this behaviour correctly?. I need to be able to read variables from the parent environment and at the same time, define a local variable without raising a duplicated definition error.

Thanks!!

[rcanepa]

I found a solution extending the environment instead of defining (with set) new values.

[kvalle]

Hi! Good to hear that you figured it out. If you get stuck again, feel free to ask new questions here.

Part 8 is newer than the rest, and thus less tested (by other people than me). So, if you find anything lacking/confusing/strange, feel free to file an issue or send a pull request!

Oh, and by the way, there is a solution branch if you feel like having a peak afterwards or if you get stuck.