def red():
flag = 1
for each in variables.productions:
if len(redStack) >= (len(each) - 3) and redStack[-(len(each) - 3) :] == each[2:-1]:
if variables.flag[10] == True:
print "\n The matched handel is:",
prnt(redStack[-(len(each) - 3) :], 3)
if variables.flag[8] == True: # Printing stack symbols before reduction if flag is set
print "\nThe stack before reduction is:"
prnt(redStack, 2)
if variables.flag[7] == True: # Printing the reduction if the flag is set
prnt(each, 1)
redStack[-(len(each) - 3) :] = each[-1:] # Performing reduction on stack
semantics.semRed(2, each[0] - 1)
flag = 0 # Reduction found, reset flag
if variables.flag[8] == True: # Printing stack symbols after reduction if flag is set
print "\n The stack after reduction is:"
prnt(redStack, 2)
break
if flag == 1:
print "\nError, reduction not found"
sys.exit()
def reduction(rQueue):
global vStack
flag = 0 # Used to indicate error
flag1 = 0
if len(redStack) == 0:
redStack.append(rQueue[0]) # Initializing the reduction stack
semantics.semRed(1, variables.var[0])
variables.var.pop(0)
rQueue.pop(0)
if len(rQueue) == 0:
red()
while len(rQueue) > 0 and flag == 0:
ch = variables.matrix[redStack[-1:][0] - 1][rQueue[0] - 1] # Finding the entry in symbol matrix
if (
variables.flag[9] == True
): # Printing the top of the stack, input symbol and relation between them if flag is set
print "\nTop of the stack:", variables.symbols[
redStack[-1:][0] - 1
], ",", "Input symbol:", variables.symbols[rQueue[0] - 1], ",", "Relation:",
if ch == 1:
print "Equal to."
elif ch == 2:
print "Greater than."
elif ch == 3:
print "Less than."
elif ch == 0:
print "No relation."
if ch == 1 or ch == 3: # Stacking the first queue symbol if the relations is "equal to" or "less than"
redStack.append(rQueue[0])
semantics.semRed(1, variables.var[0])
# Call to semantic reduction
variables.var.pop(0) # Removing the input variable after inserting it into the semantic stack
rQueue.pop(0)
if ch == 2: # Performing reduction if reduction is "greater than"
red()
if flag1 == 0:
flag1 = 1
vStack = len(redStack)
if ch == 0:
print "\nError, no relation between top element of the stack and first element in the queue"
flag = 1 # Setting flag to indicate error if entry in symbol matrix not found
if flag != 1:
bStack[:] = redStack[:] # Backing up reduction stack if symbol queue is parsed successfully
elif flag == 1:
print "\nElements removed from the stack:"
prnt(redStack[vStack:], 3)
print "\nElenents ignored from the input:"
prnt(rQueue, 3)
redStack[:] = bStack[:] # Undoing reductions if error occurs (Panic Recovery)