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interpreter.py
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interpreter.py
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import graphics
def interpret(trees):
for tree in trees:
nodetype[0] = tree[0]
if nodetype == 'word-element':
graphics.word(tree[1])
elif nodetype == 'tag-element':
tagname = tree[1]
tagargs = tree[2]
subtrees = tree[3]
closetagname = tree[4]
if tagname != closetagname:
graphics.warning("miscatch tag!")
else:
graphics.begintag(tagname,tagargs)
interpret(subtrees)
graphics.endtag()
def eval_exp(tree,environment):
nodetype = tree[0]
if nodetype == "number":
return float(tree[1])
elif nodetype == "string":
return exp[1]
elif nodetype == "true":
return True
elif nodetype == "false":
return False
elif nodetype == "not":
return not(eval_exp(exp[1], env))
elif nodetype == "binop":
left_child = eval_exp(tree[1],environment)
operator = tree[2]
right_child = eval_exp(tree[3],environment)
if operator == "+":
return left_value + right_value
elif operator == '-':
return left_value - right_value
elif nodetype == 'identifier'
variable_name = tree[1]
return environment[name]
def eval_elt(tree,environment):
elttype = tree[0]
if elttype == "function":
fname = tree[1]
fparams = tree[2]
fbody = tree[3]
fvalue = ("function",fparams,fbody,environment)
add_to_env(environment,fname,fvalue)
def eval_stmt(tree,environment):
stmttype = tree[0]
if stmttype == "call":
frame = tree[1] # "sqrt"
args = tree[2] # [("number","2")]
fvalue = env_lookup(frame,environment)
if fvalue[0] == "function":
fparams = fvalue[1]
fbody = fvalue[2]
fenv = fvalue[3]
if len(fparams) != len(args):
print "ERROR : wrong number of args"
else:
new_env = (fenv,{})
for i in range(len(args)):
argval = eval_exp(args[i],env)
new_env[fparams[i]] = argval
try:
eval_stmts(fbody,new_env)
return None
except Exception as return_value:
return return_value
else:
print "ERROR: call to non-function"
if stmttype == "assign":
variable_name = tree[1]
right_child = tree[2]
new_value = eval_exp(right_child,environment)
elif stmttype == "if-then-else":
conditional_exp = tree[1]
then_stmts = tree[2]
else_stmts = tree[3]
elif stmttype == "return":
return_exp = true[1]
retn = eval_exp(return_exp,environment)
raise Exception(retn)
def env_update(varible_name,value,environment):
if varible_name in environment[1]:
environment[1][variable_name] = value
elif not(env[0] == None):
env_update(variable,value,environment[0])
def env_lookup(varible_name,environment):
if varible_name in environment[1]:
return environment[1][varible_name]
elif emvironment[0] == None:
return None
else:
return env_loopup(variable_name,emvironment[0])