This is my third and final version of the Trac Interpreter from Recipe 577366. It processes the character stream into appropriate class objects and stores these objects on a stack.
Python, 349 lines
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import unittest
import time
EOF = ""
SEGMENT_GAP = "\xff"
INCOMPLETE, COMPLETE = range(0,2)
class TracError(Exception):
pass
class Io(object):
def __init__(self, s=""):
self.buffer = []
self.buffer += s
def pop(self, default=EOF):
try:
return self.buffer.pop(0)
except:
return default
def push(self, s):
self.buffer[0:0] += s
def delete(self, i, j):
del self.buffer[i:j]
def peek(self, count=1):
try:
chars = self.buffer[0:0 + count]
except:
chars = [EOF]
return "".join(chars)
def get_trac_protected_string(self):
chars = []
paren_count = 0
matched = False
c = self.pop()
while c != EOF and not matched:
if c == '(':
paren_count += 1
elif c == ')':
paren_count -= 1
chars.append(c)
if paren_count != 0:
c = self.pop()
else:
matched = True
if not matched:
raise TracError, "%s: can't find matching end parenthesis" %("get_trac_protected_string")
s = "".join(chars[1:-1])
return s
def list_get(list_, index, default=""):
try:
return list_[index]
except:
return default
class Expr(object):
def __init__(self):
self.chars = []
def value(self):
return "".join(self.chars)
def append(self, c):
self.chars.append(c)
def process_char(self, c):
self.append(c)
return INCOMPLETE
def __repr__(self):
return '%s(%s)' % (self.__class__.__name__, self.chars)
class Root(Expr):
def __init__(self):
Expr.__init__(self)
class Protected(Expr):
def __init__(self):
Expr.__init__(self)
class Function(Expr):
def __init__(self):
Expr.__init__(self)
self.args = []
def process_char(self, c):
if c == ',' or c == ')':
arg = self.value()
self.args.append(arg)
del self.chars[:]
if c == ')':
return COMPLETE
else:
self.append(c)
return INCOMPLETE
def __repr__(self):
return '%s(%s %s)' % (self.__class__.__name__, self.chars, self.args)
class Active(Function):
def __init__(self):
Function.__init__(self)
class Neutral(Function):
def __init__(self):
Function.__init__(self)
class Processor(object):
def __init__(self, program=""):
self.io = Io(program)
self.forms = {} # key-value storage for program variables
self.output = "" # last string printed to output by ps for unit testing
self.trace = True # flag for printing trace results of function evaluation
def tn(self, args):
self.trace = True
return ""
def tf(self, args):
self.trace = False
return ""
def ds(self, args):
key = list_get(args, 0)
value = list_get(args, 1)
self.forms[key] = value
return ""
def ps(self, args):
try:
s = list_get(args, 0)
print s
self.output = s
except:
pass
return ""
def ad(self, args):
try:
num1 = int(list_get(args, 0))
num2 = int(list_get(args, 1))
return str(num1 + num2)
except:
return ""
def su(self, args):
try:
num1 = int(list_get(args, 0))
num2 = int(list_get(args, 1))
return str(num1 - num2)
except:
return ""
def ml(self, args):
try:
num1 = int(list_get(args, 0))
num2 = int(list_get(args, 1))
return str(num1 * num2)
except:
return ""
def dv(self, args):
try:
num1 = int(list_get(args, 0))
num2 = int(list_get(args, 1))
return str(num1 / num2)
except:
return ""
def eq(self, args):
try:
s1 = list_get(args, 0)
s2 = list_get(args, 1)
eq_result = list_get(args, 2)
neq_result = list_get(args, 3)
if s1 == s2:
return eq_result
else:
return neq_result
except:
return ""
def ss(self, args):
try:
form_key = args.pop(0)
form = self.forms[form_key]
form_marked = form
for i in range(len(args)):
arg = args[i]
marker = "%s%s" % (SEGMENT_GAP, chr(i))
form_marked = form_marked.replace(arg, marker)
self.forms[form_key] = form_marked
form_list = []
form_list += form_marked
#print "ss: %s" % (form_list)
return ""
except:
return ""
def cl(self, args):
try:
form_key = args.pop(0)
form = self.forms[form_key]
form_processed = form
for i in range(len(args)):
arg = args[i]
marker = "%s%s" % (SEGMENT_GAP, chr(i))
form_processed = form_processed.replace(marker, arg)
return form_processed
except:
return ""
def initialize(self, program=""):
self.forms = {}
self.io = Io(program)
self.primitives = {"ds":self.ds, \
"ps":self.ps, \
"ss":self.ss, \
"cl":self.cl, \
"ad":self.ad, \
"su":self.su, \
"ml":self.ml, \
"dv":self.dv, \
"tn":self.tn, \
"tf":self.tf, \
"eq":self.eq \
}
self.output = []
self.stack = []
self.cur_expr = Root()
self.stack.append(self.cur_expr)
return self
def push(self, expr):
self.stack.append(expr)
self.cur_expr = expr
def pop(self):
if self.stack:
expr = self.stack.pop()
self.cur_expr = self.stack[-1]
return expr
return None
def eval(self, func_expr):
result = ""
try:
func_name = func_expr.args[0]
args = func_expr.args[1:]
primitive = self.primitives.get(func_name, None)
if primitive:
result = primitive(args)
if self.trace:
print "eval: %s %s -> [%s]" % (func_name, args, result)
except Exception, e:
raise TracError, "%s: failed - %s" %("eval", e)
return result
def run(self):
while self.io.buffer:
# print "Stack: %s" % self.stack
c = self.io.pop()
if c == '(':
self.io.push(c)
s = self.io.get_trac_protected_string()
self.cur_expr.chars += s
elif c == '#' and self.io.peek(1) == '(':
self.io.delete(0,1)
self.push(Active())
elif c == '#' and self.io.peek(2) == '#(':
self.io.delete(0,2)
self.push(Neutral())
elif c == ',':
self.cur_expr.process_char(c)
elif c in "\n\r\t":
pass
elif c == ')':
complete = self.cur_expr.process_char(c)
if complete == COMPLETE:
func_expr = self.pop()
func_result = self.eval(func_expr)
if isinstance(func_expr, Active):
self.io.push(func_result)
else:
self.cur_expr.chars += func_result
else:
self.cur_expr.process_char(c)
if self.trace:
print "Stack: %s" % self.stack
print "Forms: %s" % self.forms
print "Output: %s" % self.output
class TestTrac(unittest.TestCase):
def setUp(self):
pass
def __setup(self, program, correct=""):
self.processor = Processor()
self.processor.initialize(program)
self.processor.run()
print str(self.processor.stack)
def __test(self, program, output):
self.processor = Processor()
self.processor.initialize(program)
self.processor.run()
self.assertEqual(self.processor.output, output)
def test_1_ps(self):
self.__test("#(ps,Hello world)", "Hello world")
def test_2_equal(self):
self.__test("#(ps,#(eq,Cat,Cat,equal,not equal))", "equal")
def test_3_not_equal(self):
self.__test("#(ps,#(eq,Cat,Dog,equal,not equal))", "not equal")
def test_4_ds(self):
self.__test("#(ds,AA,Cat)#(ps,#(cl,AA))", "Cat")
def test_5_protect_parens(self):
self.__test("#(ds,AA,Cat)#(ds,BB,(#(cl,AA)))#(ps,(#(cl,BB)))", "#(cl,BB)")
def test_6_neutral_func(self):
self.__test("#(ds,AA,Cat)#(ds,BB,(#(cl,AA)))#(ps,##(cl,BB))", "#(cl,AA)")
def test_7_indirection(self):
self.__test("#(ds,AA,Cat)#(ds,BB,(#(cl,AA)))#(ps,#(cl,BB))", "Cat")
def test_8_ss(self):
self.__test("#(ds,AA,Hello X)#(ss,AA,X)#(ps,#(cl,AA,world))", "Hello world")
def test_9_factorial(self):
self.__test("""
#(ds,Factorial,(#(eq,X,1,1,(#(ml,X,#(cl,Factorial,#(su,X,1)))))))
#(ss,Factorial,X)
#(ps,#(cl,Factorial,5))
""", "120")
if __name__ == "__main__":
print __file__
unittest.main()
|
This is even shorter than the Dragon version in Recipe 577396.
The processor handles the character stream a character at a time into the current object which may be either a string, a TRAC active function, or a TRAC neutral function, which is pushed on to the TRAC object stack.
As each function is completed, it is executed, and its result is pushed back on to the stack for neutral functions or back into the character stream for active functions. This continues until the character stream is exhausted and all its functions executed.
I think this is the most straightforward of the three versions. The original Mooers algorithm is close to spaghetti code. The recursive descent approach is overkill because the TRAC language is so simple that there are few tokens and the TRAC algorithm really just moves characters from one place to another. Plus the use of an explicit stack in this recipe makes it easier to visualize IMO than the implicit stack used in the recursive descent version.
Those so inclined may find it interesting to compare this with the other two versions:
http://code.activestate.com/recipes/577366-trac-interpreter-sixties-programming-language/ . http://code.activestate.com/recipes/577396-trac-interpreter-dragon-style/
For a discussion of the TRAC language, see http://code.activestate.com/recipes/577366-trac-interpreter-sixties-programming-language/ .
