Context.md

Contextual Object

One of the reasons the original code clean-up failed is that the one-file interpreter relied too heavily on global variable; in order to access values such as flag settings, input levels and context values (the ones used with n), variables had to be scoped as global within functions. Ignoring the fact that global variables are generally a bad programming practice, this was an issue because you can't access global variables from one file inside another file.

The best solution to this is to have a special Context class that contains all the variables that were previously global. The definition of the class might look like:

class Context:
    def __init__(self):
        self.stack = []
        self.register = 0
        # and so on

At the start of the interpreter, an instance of Context called ctx (think ctx = Context()) will be created. This will need to be passed between element functions, meaning they all need a ctx parameter.

The Explicit Way

(for example, this could be vyxal.py)

# Simulate main.py

import elements

class Context:
    def __init__(self):
        self.reverse_arguments = False


ctx = Context()
ctx.reverse_arguments = False

lst = [1, 2, 3, 4]
print(lst)
x = elements.pop(lst, 2, ctx)
print(x, lst)

(and this could be elements.py)

def pop(stack, n=1, *, ctx):
    ret = [stack.pop() for i in range(n)]
    if ctx.reverse_arguments: ret = ret[::-1]
    return ret