fp_exercise3.py

def zero(s):
    if s[0] == "0":
        return s[1:]
 
def one(s):
    if s[0] == "1":
        return s[1:]
 
"""
def rule_sequence(s, rules):
    for rule in rules:
        s = rule(s)
        if s == None:
            break

    return s
"""
 
print rule_sequence('0101', [zero, one, zero])
# => 1
 
print rule_sequence('0101', [zero, zero])
# => None
 
# Reimplement rule_sequence as a recursive function.
# Make sure that when it is run, it returns the results shown above.