"""The interpreter"""
from .parser import parse
from .tokenize import tokenize

class ParseError(Exception):
    pass

def callIMP(chars, env=None):
    """
        The entry point for everyone who wants to call
        IMP from within Python. The function either
        returns the value or None, if the call did not
        succeed.

        chars -- the string to evaluate
        env   -- a environment to bootstrap the imp
                 environment with

        returns -- the IMP environment | None
    """
    if not chars: return None
    tokens = tokenize(chars)
    if not tokens: raise ParseError("tokens could not be generated")
    parsed = parse(tokens)
    if not parsed or not parsed.value: raise ParseError("tokens could not be parsed")
    ast = parsed.value
    if not env: env = {}
    ast.eval(env)
    return env