def __apply1(self, arg):
#sys.stdin.write('inside apply1')
sym = self.symbol.getName()
if sym == "car":
return arg.getCar()
elif sym == "cdr":
return arg.getCdr()
elif sym == "number?":
return BoolLit.getInstance(arg.isNumber())
elif sym == "symbol?":
return BoolLit.getInstance(arg.isSymbol())
elif sym == "null?":
return BoolLit.getInstance(arg.isNull())
elif sym == "pair?":
return BoolLit.getInstance(arg.isPair())
elif sym == "procedure?":
return BoolLit.getInstance(arg.isProcedure())
elif sym == "write":
arg.print(-1)
return Nil.getInstance()
elif sym == "display":
StrLit.DoubleQuotes = False
arg.print(-1)
StrLit.DoubleQuotes = True
return Nil.getInstance()
elif sym == "load":
#sys.stdout.write('load successful')
if not arg.isString():
self._error("first argument error")
return Nil.getInstance()
f = arg.getStrVal()
#sys.stdout.write('before try')
try:
scan = Scanner(open(f))
#sys.stdout.write('1')
build = TreeBuilder()
#sys.stdout.write('2')
parse = Parser(scan, build)
#sys.stdout.write('3')
head = parse.parseExp()
#sys.stdout.write('4')
while head != None:
head.eval(BuiltIn.env)
#sys.stdout.write('loop1')
head = parse.parseExp()
#sys.stdout.write('loop2')
except IOError:
self._error("file not found " + f)
return Nil.getInstance()
else:
self._error("first argument error")
return Nil.getInstance()
def __evaluate(self, exp, env):
if exp.isNull():
return Nil.getInstance()
cnd = exp.getCar()
if Special.util.length(cnd) < 1:
self._error("first cond error")
return Nil.getInstance()
name = cnd.getCar()
rest = cnd.getCdr()
if name.isSymbol():
if test.getName() == "else":
if not (rest.isNull() or exp.getCdr().isNull()):
self._error("second cond error")
return Nil.getInstance()
return Special.util.begin(rest, env)
val = test.eval(env)
if val != BoolLit.getInstance(False):
if rest.isNull():
return val
t = rest.getCar()
if t.isSymbol():
if t.getName() == "=>":
if Special.util.length(rest) != 2:
self._error("third cond error")
return Nil.getInstance()
func = body.getCdr().getCar().eval(env)
return func.apply(val)
return Special.util.begin(body, env)
else:
return self.__evalClauses(exp.getCdr(), env)
def __apply2(self, arg1, arg2):
#sys.stdout.write('inside apply2')
sym = self.symbol.getName()
if sym == "eq?":
return BoolLit.getInstance(arg1 is arg2)
elif sym == "cons":
return Cons(arg1, arg2)
elif sym == "set-car!":
arg1.setCar(arg2)
return Nil.getInstance()
elif sym == "set-cdr!":
arg1.setCdr(arg2)
return Nil.getInstance()
elif sym == "eval":
if arg2.isEnvironment():
return arg1.eval(arg2)
self._error("second argument error")
return Nil.getInstance()
elif sym == "apply":
return arg1.apply(arg2)
else:
if sym[0] == "b":
pass
if len(sym) == 2:
if arg1.isNumber():
if arg2.isNumber():
return self.__IntOps(arg1.getIntVal(),
arg2.getIntVal())
self._error("argument error")
return Nil.getInstance()
self._error("argument error")
return Nil.getInstance()
def eval(self, exp, env):
if(Special.util.length(exp) != 2):
self._error('invalid expression: incorrect number of arguments')
return Nil.getInstance()
expressions = exp.getCdr()
while(not (expressions.isNull())):
clause = expressions.getCar()
if(Special.util.length(clause)<1):
self._error('invalid expression: invalid cond clause')
return Nil.getInstance()
test = clause.getCar()
body = clause.getCdr()
first = body.getCar()
if(first == '=>'):
body = body.getCdr().getCar().eval(env)
else:
body = body.eval(env)
if(test.isSymbol()):
if(test.getName()=='else'):
return body.apply(test)
test = test.eval(env)
if(test == BoolLit(True)):
return body.apply(test)
expressions = expressions.getCdr()
return Nil.getInstance()
def __IntOps(self, arg1, arg2):
sym = self.symbol.getName()
if sym == "b+":
return IntLit(arg1 + arg2)
elif sym == "b-":
return IntLit(arg1 - arg2)
elif sym == "b*":
return IntLit(arg1 * arg2)
elif sym == "b/":
return IntLit(arg1 / arg2)
elif sym == "b=":
return BoolLit.getInstance(arg1 == arg2)
elif sym == "b<":
return BoolLit.getInstance(arg1 < arg2)
else:
self._error("Unknown BuiltIn function")
return Nil.getInstance()
def eval(self, exp, env):
condition = exp.getCdr().getCar()
if condition.eval(env) == BoolLit.getInstance(True):
return exp.getCdr().getCdr().getCar().eval(env)
elif not (exp.getCdr().getCdr().getCdr() == Nil.getInstance()):
return exp.getCdr().getCdr().getCdr().getCar().eval(env)
else:
return StrLit("else expression not found")
def eval(self, exp, env):
#sys.stdout.write('inside apply.eval')
t = Special.util.length(exp)
if t < 3 or t > 4:
self._error("special if error")
return Nil.getInstance()
temp = exp.getCdr().getCar()
temp1 = exp.getCdr().getCdr().getCar()
if t == 3:
eexp = Nil.getInstance()
else:
eexp = exp.getCdr().getCdr().getCdr().getCar()
if temp.eval(env) != BoolLit.getInstance(False):
return temp1.eval(env)
else:
return eexp.eval(env)
def eval(self, exp, env):
n = Special.util.length(exp)
# Test for a valid if statement
if (n < 3 or n > 4):
self._error(
'invalid expression, incorrect number of arguments for if statement'
)
return Nil.getInstance()
# extract the conditional test from the if statement
testExp = exp.getCdr().getCar()
# extract the expression to evaluate if the conditional evaluates to true
trueExp = exp.getCdr().getCdr().getCar()
# extract the expression to evaluate if the conditional evaluates to false
if (n == 3):
elseExp = Nil.getInstance(
) # Else expression is unspecified, return Unspecified if implemented
else:
elseExp = exp.getCdr().getCdr().getCdr().getCar()
# evaluate the test and return the desired expression
if (testExp.eval(env) == BoolLit.getInstance(True)):
return trueExp.eval(env)
else:
return elseExp.eval(env)
def buildBoolLit(self,b):
return BoolLit.getInstance(b)
def apply(self, args):
argLength = self.util.length(args)
name = self.symbol.strVal
if name == "b+": #Binary Addition
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
sum = args.getCar().intVal + args.getCdr().getCar().intVal
return IntLit(sum)
elif name == "b-": #Binary Subtraction
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
diff = args.getCar().intVal - args.getCdr().getCar().intVal
return IntLit(diff)
elif name == "b*": #Binary Multiplication
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
return IntLit(args.getCar().intVal * args.getCdr().getCar().intVal)
elif name == "b/": #Binary Division
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
return IntLit(args[0].intVal / args.getCdr().getCar().intVal)
elif name == "number?": #Check if is a number
if argLength is not 1:
return self.invalidArgCount()
if args.getCar().isNumber():
return BoolLit.getInstance(True)
return BoolLit.getInstance(False)
elif name == "b=":
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
return BoolLit.getInstance(True) if args.getCar(
).intVal == args.getCdr().getCar().intVal else BoolLit.getInstance(
False)
elif name == "b<":
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isNumber() or not args.getCdr().getCar(
).isNumber():
return self.invalidArgType()
return BoolLit.getInstance(True) if args.getCar(
).intVal < args.getCdr().getCar().intVal else BoolLit.getInstance(
False)
elif name == "null?":
if argLength is not 1:
return self.invalidArgCount()
if args.getCar().isNull():
return BoolLit.getInstance(True)
return BoolLit.getInstance(False)
elif name == "procedure?":
if argLength is not 1:
return self.invalidArgCount()
if args.getCar().isProcedure():
return BoolLit.getInstance(True)
return BoolLit.getInstance(False)
elif name == "pair?":
if argLength is not 1:
return self.invalidArgCount()
return BoolLit.getInstance(
True) if args.getCar().isPair() else BoolLit.getInstance(False)
elif name == "cons":
if argLength is not 2:
return self.invalidArgCount()
return Cons(args.getCar(), args.getCdr().getCar())
elif name == "car":
if argLength is not 1:
return self.invalidArgCount()
if not args.getCar().isPair():
return self.invalidArgType()
return args.getCar().getCar()
elif name == "cdr":
if argLength is not 1:
return self.invalidArgCount()
if not args.getCar().isPair():
return self.invalidArgType()
return args.getCar().getCdr()
elif name == "set-car!":
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isPair():
return self.invalidArgType()
args.getCar().setCar(args.getCdr().getCar())
return Nil.getInstance()
elif name == "set-cdr!":
if argLength is not 2:
return self.invalidArgCount()
if not args.getCar().isPair():
return self.invalidArgType()
args.getCar().setCdr(args.getCdr().getCar())
return Nil.getInstance()
elif name == "eq?":
if args.getCar().isSymbol() and args.getCdr().getCar().isSymbol():
arg1_name = args.getCar().getName()
arg2_name = args.getCdr().getCar().getName()
return BoolLit.getInstance(arg1_name == arg2_name)
return BoolLit.getInstance(args.getCar() == args.getCdr().getCar())
#load
elif name == "load":
if not args.getCar().isString():
return self.invalidArgType()
filename = args.getCar().strVal
try:
scanner = Scanner(open(filename))
builder = TreeBuilder()
parser = Parser(scanner, builder)
root = parser.parseExp()
while root != None:
root.eval(BuiltIn.env)
root = parser.parseExp()
except IOError:
self._error("could not find file " + filename)
return Nil.getInstance() # or Unspecific.getInstance()
#read, calls parser and returns a parse tree
elif name == "read":
scanner = Scanner(sys.stdin)
builder = TreeBuilder()
parser = Parser(scanner, builder)
#return parse tree here
if parser != None:
return parser.parseExp()
return Ident('End of Parse Tree')
#write, calls pretty printer
elif name == "write":
if argLength is not 1:
return self.invalidArgCount()
args.getCar().print(-1)
return Nil.getInstance()
#display, calls pretty printer
elif name == "display":
if argLength is not 1:
return self.invalidArgCount()
StrLit.include_quote = 0
args.getCar().print(-1)
StrLit.include_quote = 1
return Nil.getInstance()
#eval, calls python eval function
elif name == 'eval':
if argLength is not 2:
return self.invalidArgCount()
if args.getCdr().getCar().isEnvironment():
return args.getCar().eval(args.getCdr().getCar())
return self.invalidArgType()
#apply, calls python apply function
elif name == "apply":
if argLength is not 2:
return self.invalidArgCount()
return args.getCar().apply(args.getCdr().getCar())
#interaction-environment, returns a pointer to interpreter's global environment
elif name == "interaction-environment":
return BuiltIn.env
#newline without optional port argument
elif name == "newline":
sys.stdout.write('\n')
sys.stdout.flush()
return Nil.getInstance()
return StrLit("Error: BuiltIn.apply not yet implemented for " +
self.symbol)
def apply(self, args):
# Retrive the length of the argument
length = BuiltIn.util.length(args)
# Error check for invalid number of arguments
if (length > 2):
self._error('invalid expression: too many arguments')
return Nil.getInstance()
# Extract the name
name = self.symbol.getName()
# Apply for arguments of length 0
if (length == 0):
if (name == "read"):
scanner = Scanner(sys.stdin)
builder = TreeBuilder()
parser = Parser(scanner, builder)
result = parser.parseExp()
if (result != None):
return result
return Ident('end-of-file')
if (name == "newline"):
sys.stdout.write('\n')
sys.stdout.flush()
return Nil.getInstance()
if (name == "interaction-environment"):
return self.env
self._error('unknown built-in function')
return Nil.getInstance()
# Apply for arguments of length 1
if (length == 1):
# Retrieve the argument
arg1 = args.getCar()
# Apply for load
if (name == "load"):
if (not arg1.isString()):
self._error("wrong type of argument")
return Nil.getInstance()
filename = arg1.getStrVal()
try:
scanner = Scanner(open(filename))
builder = TreeBuilder()
parser = Parser(scanner, builder)
root = parser.parseExp()
while root != None:
root.eval(BuiltIn.env)
root = parser.parseExp()
except IOError:
self._error("could not find file " + filename)
return Nil.getInstance() # or Unspecific, if implemented
# Apply for car
if (name == "car"):
return arg1.getCar()
# Apply for cdr
if (name == "cdr"):
return arg1.getCdr()
# Apply for number?
if (name == "number?"):
return BoolLit.getInstance(arg1.isNumber())
# Apply for symbol?
if (name == "symbol?"):
return BoolLit.getInstance(arg1.isSymbol())
# Apply for null?
if (name == "null?"):
return BoolLit.getInstance(arg1.isNull())
# Apply for pair?
if (name == "pair?"):
return BoolLit.getInstance(arg1.isPair())
# Apply for procedure?
if (name == "procedure?"):
return BoolLit.getInstance(arg1.isProcedure())
# Apply for write
if (name == "write"):
arg1.print(-1)
return Nil.getInstance()
# Apply for display
if (name == "display"):
StrLit.printQuotes = False
arg1.print(-1)
StrLit.printQuotes = True
return Nil.getInstance()
self._error('unknown built-in function')
return Nil.getInstance()
# Apply for arguments of length 2
if (length == 2):
# Retrieve the two arguments
arg1 = args.getCar()
arg2 = args.getCdr().getCar()
if (name == "eq?"):
if (arg1.isSymbol()):
if (arg2.isSymbol()):
name1 = arg1.getName()
name2 = arg2.getName()
return BoolLit.getInstance(name1 == name2)
else:
return BoolLit.getInstance(False)
return BoolLit.getInstance(arg1 == arg2)
if (name == "cons"):
return Cons(arg1, arg2)
if (name == "set-car!"):
arg1.setCar(arg2)
return Nil.getInstance()
if (name == "set-cdr!"):
arg1.setCdr(arg2)
return Nil.getInstance()
if (name == "eval"):
return arg1.eval(arg2)
if (name == "apply"):
return arg1.apply(arg2)
if (name[0] == 'b'):
if (arg1.isNumber()):
if (arg2.isNumber()):
arg1 = arg1.getIntVal()
arg2 = arg2.getIntVal()
if (name == 'b+'):
return IntLit(arg1 + arg2)
if (name == 'b-'):
return IntLit(arg1 - arg2)
if (name == 'b*'):
return IntLit(arg1 * arg2)
if (name == 'b/'):
return IntLit(arg1 / arg2)
if (name == 'b='):
return BoolLit.getInstance(arg1 == arg2)
if (name == 'b<'):
return BoolLit.getInstance(arg1 < arg2)
self._error('unknown built-in function')
return Nil.getInstance()
else:
self._error('invalid argument type')
return Nil.getInstance()
else:
self._error('invalid argument type')
return Nil.getInstance()
self._error('unknown built-in function')
return Nil.getInstance()
def apply(self, args):
if args == None:
return None
symbolName = self.symbol.getName()
arg1 = args.getCar()
if arg1 == None or arg1.isNull():
arg1 = Nil()
arg2 = args.getCdr()
if arg2 == None or arg2.isNull():
arg2 = Nil()
if symbolName == '+':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return IntLit(x + y)
else:
print('bad argument for +')
return StrLit("")
elif symbolName == '-':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return IntLit(x - y)
else:
print('bad argument for -')
return StrLit("")
elif symbolName == '*':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return IntLit(x * y)
else:
print('bad argument for *')
return StrLit("")
elif symbolName == '/':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return IntLit(x / y)
else:
print('bad argument for /')
return StrLit("")
elif symbolName == '=':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return BoolLit(x == y)
else:
print('bad argument for =')
elif symbolName == '<':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return BoolLit(x < y)
else:
print('bad argument for <')
elif symbolName == '>':
if arg1.isNumber() and arg2.isNumber():
x = arg1.getIntVal()
y = arg2.getIntVal()
return BoolLit(x > y)
else:
print('bad argument for >')
elif symbolName == 'car':
if arg1.isNull():
return arg1
return arg1.getCar()
elif symbolName == 'cdr':
if arg1.isNull():
return arg1
return arg1.getCdr()
elif symbolName == 'cons':
return Cons(arg1, arg2)
elif symbolName == 'set-car!':
arg1.setCar(arg2)
return arg1
elif symbolName == 'set-cdr!':
arg1.setCdr(arg2)
return arg1
elif symbolName == 'symbol?':
return BoolLit(arg1.isSymbol())
elif symbolName == 'number?':
return BoolLit(arg1.isNumber())
elif symbolName == 'null?':
return BoolLit(arg1.isNull())
elif symbolName == 'pair?':
return BoolLit(arg1.isPair())
elif symbolName == 'eq?':
if (arg1.isBool() and arg2.isBool()) or (arg1.isNumber()
and arg2.isNumber()) or (
arg1.isString()
and arg2.isString()):
return BoolLit(arg1 == arg2)
elif arg1.isSymbol() and arg2.isSymbol():
return BoolLit(arg1.getName() == arg2.getName())
elif arg1.isNull() and arg2.isNull():
return BoolLit(True)
elif arg1.isPair() and arg2.isPair():
frontArgs = Cons(arg1.getCar(), Cons(arg2.getCar(), Nil))
backArgs = Cons(arg1.getCdr(), Cons(arg2.getCdr(), Nil))
return BoolLit(apply(frontArgs) and apply(backArgs))
return BoolLit(false)
elif symbolName == 'procedure?':
return BoolLit(arg1.isProcedure)
elif symbolName == 'display':
return arg1
elif symbolName == 'newline':
return StrLit("", false)
elif symbolName == 'exit' or symbolName == 'quit':
exit()
elif symbolName == 'write':
arg1.print(0)
elif symbolName == 'eval':
return arg1
elif symbolName == 'apply':
return arg1.apply(arg2)
elif symbolName == 'read':
parser = Parser()
return parser.parseExp()
elif symbolName == 'interaction-environment':
self.env.print(0)
else:
arg1.print(0)
return Nil()
return StrLit('>')
def eval(self, exp, env):
cond = exp.getCdr()
while(cond.getCdr() != Nil.getInstance() and cond.getCar().getCar().eval(env) == BoolLit.getInstance(False)):
cond = cond.getCdr()
if cond == Nil.getInstance():
return Nil.getInstance()
else:
return cond.getCar().getCdr().getCar().eval(env)
def apply(self, args):
## The easiest way to implement BuiltIn.apply is as an
## if-then-else chain testing for the different names of
## the built-in functions. E.g., here's how load could
## be implemented:
# if name == "load":
# if not arg1.isString():
# self._error("wrong type of argument")
# return Nil.getInstance()
# filename = arg1.getStrVal()
# try:
# scanner = Scanner(open(filename))
# builder = TreeBuilder()
# parser = Parser(scanner, builder)
# root = parser.parseExp()
# while root != None:
# root.eval(BuiltIn.env)
# root = parser.parseExp()
# except IOError:
# self._error("could not find file " + filename)
# return Nil.getInstance() # or Unspecific.getInstance()
# this may or may not work
# get args (arg 1 is the car, arg 2 is the car of the cdr)
if args == None:
return Nil.getInstance()
name = self.symbol.getName()
car = args.getCar()
if car.isNull():
car = Nil.getInstance()
cdr = args.getCdr()
# if there is no arg 2, just set it to nil
if cdr.isNull():
cdr = Nil.getInstance()
# otherwise arg2 is the car of the cdr
else:
cdr = cdr.getCar()
if name == "b+":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return IntLit(x + y)
else:
return StrLit("Invalid arguments for b+")
elif name == "b-":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return IntLit(x - y)
else:
return StrLit("Invalid arguments for b-")
elif name == "b*":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return IntLit(x * y)
else:
return StrLit("Invalid arguments for b*")
elif name == "b/":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return IntLit(x / y)
else:
return StrLit("Invalid arguments for b/")
elif name == "b=":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return BoolLit.getInstance(x == y)
else:
return StrLit("Invalid arguments for b=")
elif name == "b<":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return BoolLit.getInstance(x < y)
else:
return StrLit("Invalid arguments for b<")
elif name == "b>":
if car.isNumber() and cdr.isNumber():
x = car.intVal
y = cdr.intVal
return BoolLit.getInstance(x > y)
else:
return StrLit("Invalid arguments for b>")
elif name == "car":
if car.isPair():
return car.getCar()
return StrLit("Wrong number of arguements")
elif name == "cdr":
if car.isPair():
return car.getCdr()
return StrLit("Wrong number of arguements")
elif name == "cons":
if cdr.isPair():
return Cons(car, cdr)
return StrLit("Wrong number of arguements")
elif name == "set-car!": #does this work??
car.setCar(cdr)
return car
elif name == "set-cdr!": #does this work??
car.setCdr(cdr)
return car
elif name == "symbol?":
return BoolLit.getInstance(car.isSymbol())
elif name == "number?":
return BoolLit.getInstance(car.isNumber())
elif name == "null?":
return BoolLit.getInstance(car == Nil.getInstance())
elif name == "pair?":
return BoolLit.getInstance(car.isPair())
elif name == "eq?": #come back to this
if car.isBool() and cdr.isBool():
return BoolLit.getInstance(car.boolVal == cdr.boolVal)
elif car.isNumber() and cdr.isNumber():
return BoolLit.getInstance(car.intVal == cdr.intVal)
elif car.isSymbol() and cdr.isSymbol():
return BoolLit(car.getName().equals(cdr.getName()))
elif car == Nil.getInstance():
return BoolLit.getInstance(True)
elif (car.isPair() and cdr.isPair()):
opener = Cons(car.getCar(),
Cons(cdr.getCar(), Nil.getInstance()))
closer = Cons(car.getCdr(),
Cons(cdr.getCdr(), Nil.getInstance()))
return BoolLit(apply(opener).boolVal and apply(closer).boolVal)
elif name == "procedure?":
return BoolLit.getInstance(car.isProcedure())
elif name == "display":
return car
elif name == "newline": #come back to this
StrLit("")
elif name == "read":
parser = Parser(Scanner(sys.stdin)) #com back to this
return parser.parseExp()
elif name == "write": #come back to this
car.print(0)
return StrLit("")
elif name == "eval": #come back
return car
elif name == "apply": #come back
return car.apply(cdr)
elif name == "interaction-development": #come back
interaction_environment.print(0)
elif name == "load": #come back
if not car.isString():
self._error("wrong type of argument")
return Nil.getInstance()
filename = arg1.getStrVal()
try:
scanner = Scanner(open(filename))
builder = TreeBuilder()
parser = Parser(scanner, builder)
root = parser.parseExp()
while root != None:
root.eval(BuiltIn.env)
root = parser.parseExp()
except IOError:
self._error("could not find file " + filename)
return Nil.getInstance() # or Unspecific.getInstance()
else:
car.print(0)
return Nil.getInstance()
return StrLit(">")