# addingUpElementsOfAList.py
#   P. Conrad for CS5nm, 11/17/08
#   Show how to add up all elements of a list of numbers using recursion


# check_expect checks whether a function produces the expected result
# consumes:
#     test: a string describing the test
#    check: the value we are testing (typically result of a function call)
#   expect: the value we are expecting (typically a literal value)
# produces:
#    nothing (there is no return value)
# side effect:
#    prints a message indicating whether the test passed or failed

def check_expect(test,check,expect):
    if (check == expect):
        print "Test " + test + " passed."
    else:
        print "Test " + test + " failed: expected " + str(expect)  + \
              " but I got " + str(check)


def isEmpty(myList):
    return len(myList)==0


def first(myList):
    return myList[0]

def rest(myList):
    return myList[1:]

# consumes: a list of numbers
# produces: the sum of those numbers

def sumListNums(myList):
    if (isEmpty(myList)):
        return 0
    elif len(myList)==1:
        return first(myList)
    else:
        return first(myList) + sumListNums(rest(myList))


check_expect("sumListNums([2,3,4])",
             sumListNums([2,3,4]),
             9)

check_expect("sumListNums([])",
             sumListNums([]),
             0)