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tlis.py
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tlis.py
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import math
import operator as op
#Explicitly stating Scheme objects
Symbol = str
List = list
Number = (int, float)
Env = dict
def parse(program):
'''parse combines tokenize and readFromTokens'''
return readFromTokens(tokenize(program))
def tokenize(chars):
return chars.replace('(', ' ( ').replace(')', ' ) ').split()
def readFromTokens(tokens):
if len(tokens) == 0:
raise ValueError("Unexpected end of line while parsing")
token = tokens.pop(0)
if token == '(':
L = []
try :
while (tokens[0] != ')'):
L.append(readFromTokens(tokens))
except IndexError:
raise ValueError("Unexpected end of line while parsing")
tokens.pop(0)
return L
elif token == ')':
raise SyntaxError("Missing (")
else:
return atom(token)
def atom(token):
try: return int(token)
except ValueError:
try: return float(token)
except ValueError:
return Symbol(token)
def standardEnv():
env = Env()
env.update(vars(math))
env.update({
"+" : op.add, "-" : op.sub, "*" : op.mul, "/" : op.div
})
return env
globalEnv = standardEnv()
def eval(x, env = globalEnv):
print x
if isinstance(x, Symbol):
return env[x]
program = "(begin (define r 10) (* pi (* r r)))"
program3 = "(define r 10)"
##program2 = "(define circle-area (lambda (r) (* pi (* r r))))"
print parse(program3)