quiz3-14.py

# --------------
# User Instructions
#
# Complete the code for the compiler by completing the constructor
# for the patterns alt(x, y) and oneof(chars). 

def lit(s):         return lambda Ns: set([s]) if len(s) in Ns else null
def alt(x, y):      return lambda Ns: set([opr for opr in list(x(Ns)|y(Ns)) if len(opr) in Ns])
def star(x):        return lambda Ns: opt(plus(x))(Ns)
def plus(x):        return lambda Ns: genseq(x, star(x), Ns, startx=1) #Tricky
def oneof(chars):   return lambda Ns: set([opr for opr in chars if 1 in Ns])
def seq(x, y):      return lambda Ns: genseq(x, y, Ns)
def opt(x):         return alt(epsilon, x)
dot = oneof('?')    # You could expand the alphabet to more chars.
epsilon = lit('')   # The pattern that matches the empty string.

null = frozenset([])

def test():
    
    f = lit('hello')
    assert f(set([1, 2, 3, 4, 5])) == set(['hello'])
    assert f(set([1, 2, 3, 4]))    == null 
    
    g = alt(lit('hi'), lit('bye'))
    assert g(set([1, 2, 3, 4, 5, 6])) == set(['bye', 'hi'])
    assert g(set([1, 3, 5])) == set(['bye'])
    
    h = oneof('theseletters')
    assert h(set([1, 2, 3])) == set(['t', 'h', 'e', 's', 'l', 'r'])
    assert h(set([2, 3, 4])) == null
    
    return 'tests pass'

print test()