class ParseExpression(object):
'''
Parses a lambda expression into a representative
data structure composed of objects in the LambdaForms
module.
'''
def __init__(self):
self.table = LookupTable()
def go(self, string):
self.eval(string)
def parse(self, string):
self.val = self.__parse(string)
print('\n' + str(string))
print(str(self.val) + '\n')
return self.val
def eval(self, string):
self.result = self.parse(string).eval()
print('\n' + str(self.result) + '\n')
return self.result
def __handleAbs(self, st):
m = re.match(r'^\\+([a-zA-Z]+)\.(.+)$', st)
var = m.group(1)
boundVars = []
for c in var:
varid = self.table.rename(c)
boundVars.append(Identifier(c, varid))
expr = m.group(2)
result = Abstraction(boundVars, self.__parse(expr))
for c in var:
self.table.unbind(c)
return result
def __handleApp(self, st):
count = 0
begin = -1
lst = []
for i in range(len(st)):
if st[i] == '(':
if begin == -1:
begin = i + 1
count += 1
elif st[i] == ')':
count -= 1
if count == 0:
lst.append(st[begin:i])
begin = -1
elif count == 0:
lst.append(st[i])
return Application([self.__parse(x) for x in lst])
def __parse(self, st):
if len(st) == 1:
return Identifier(st, self.table.lookup(st))
elif len(st) > 0:
c = st[0]
if c == '\\': #Expression is an abstraction
return self.__handleAbs(st)
elif c == '(' or c.isalpha(): #Expression is an application
return self.__handleApp(st)
else:
#print('len(st) < 0?')
raise IndexError
def __init__(self):
self.table = LookupTable()
