from operator import add, mul
from rlist import *
from ucb import main

def tokenize(s):
    """Splits the provided string into a list of tokens."""
    s = s.replace('(', ' ( ')
    s = s.replace(')', ' ) ')
    return s.split()

def numberize(exp):
    """Converts exp to a number if possible, otherwise leaves it alone."""
    try:
        return int(exp)
    except ValueError:
        try:
            return float(exp)
        except ValueError:
            return exp
        
def read_exp(tokens):
    """Given a list of tokens, returns the first calculator expression (either
    a number, operator, or combination)."""
    if not tokens:
        raise SyntaxError('unexpected end of input')
    token = tokens.pop(0)
    if token == '(':
        exp = read_tail(tokens)
        if exp is nil:
            raise SyntaxError('empty combination')
        return exp
    elif token == ')':
        raise SyntaxError('unexpected )')
    else:
        return numberize(token)
    
def read_tail(tokens):
    """Reads up to and including the first mismatched close parenthesis, then
    forms a combination out all of the values read up to that point."""
    if tokens[0] == ')':
        tokens.pop(0)
        return nil
    return Pair(read_exp(tokens), read_tail(tokens))

def calc_eval(exp):
    """Evaluates a calculator expression."""
    if isinstance(exp, Pair):
        return calc_apply(exp.car, map_rlist(calc_eval, exp.cdr))
    else:
        return exp
    
def calc_apply(op, args):
    """Applies an operator to an rlist of arguments."""
    length = len_rlist(args)
    if op == '+':
        return reduce_rlist(add, 0, args)
    elif op == '*':
        return reduce_rlist(mul, 1, args)
    elif op == '-':
        if length == 0:
            raise TypeError('not enough arguments')
        elif length == 1:
            return -args.car
        else:
            return args.car - reduce_rlist(add, 0, args.cdr)
    elif op == '/':
        if length == 0:
            raise TypeError('not enough arguments')
        elif length == 1:
            return 1 / args.car
        else:
            return args.car / reduce_rlist(mul, 1, args.cdr)
    else:
        raise NameError('unknown operator {}'.format(op))
    
@main
def repl():
    while True:
        try:
            line = input('> ')
            exp = read_exp(tokenize(line))
            print(calc_eval(exp))
        except (KeyboardInterrupt, EOFError):
            print('Calculation complete.')
            return
        except (SyntaxError, TypeError, NameError, ValueError) as e:
            print(type(e).__name__ + ':', e)