文法：
E->E+T | T
T->T*F | F
F->(E)|i
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消除左递归：
E->TH
H->+TH|e(空)
T->FY
Y->*FY|e
F->(E)|i
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非终结符集：
E，H，T，Y，F
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终结符集:
i,+,*,(,),#
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求出非终结符的FIRST集和FOLLOW集
FIRST(E)={(,i} FOLLOW = {),#}
FIRST(H)={+,e} FOLLOW = {),#}
FIRST(T)={(,i} FOLLOW = {+,),#}
FIRST(Y)={*,e} FOLLOW = {+,),#}
FIRST(F)={(,i} FOLLOW = {*,+,),#}
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生成的预测分析表如下:
预测分析器模型图:
#!/usr/env python
# -*- coding: UTF-8 -*-
"""
Created by zhoupan on 12/5/16.
"""
"""
文法：
E->E+T | T
T->T*F | F
F->(E)|i
消除左递归：
E->TH
H->+TH|e(一普赛肋)
T->FY
Y->*FY|e
F->(E)|i
非终结符：
E，H，T，Y，F
终结符:
i,+,*,(,),#
"""
# 手动构造预测分析表
dists = {
('E', 'i'): 'TH',
('E', '('): 'TH',
('H', '+'): '+TH',
('H', ')'): 'e',
('H', '#'): 'e',
('T', 'i'): 'FY',
('T', '('): 'FY',
('Y', '+'): 'e',
('Y', '*'): '*FY',
('Y', ')'): 'e',
('Y', '#'): 'e',
('F', 'i'): 'i',
('F', '('): '(E)',
}
# 构造终结符集合
Vt = ('i', '+', '*', '(', ')')
# 构造非终结符集合
Vh = ('E', 'H', 'T', 'Y', 'F')
# 获取输入栈中的内容
def printstack(stack):
rtu = ''
for i in stack:
rtu += i
return rtu
# 得到输入串剩余串
def printstr(str, index):
rtu = ''
for i in range(index, len(str), 1):
rtu += str[i]
return rtu
# 定义error函数
def error():
print('Error')
exit()
# 总控程序
def masterctrl(str):
'''
总控程序，用于进程文法的判断
'''
# 用列表模拟栈
stack = []
location = 0
# 将#号入栈
stack.append(str[location])
# 将文法开始符入栈
stack.append('E')
# 将输入串第一个字符读进a中
location += 1
a = str[location]
printstack(stack)
flag = True
count = 0
print('%d\t\t%s\t\t%s' % (count, printstack(stack), printstr(str, location)))
while flag:
if count == 0:
pass
else:
if x in Vt:
print('%d\t\t%s\t\t%s' % (count, printstack(stack), printstr(str, location)))
else:
print('%d\t\t%s\t\t%s\t\t%s->%s' % (count, printstack(stack), printstr(str, location), x, s))
x = stack.pop()
if x in Vt:
if x == str[location]:
location += 1
a = str[location]
else:
error()
elif x == '#':
if x == a:
flag = False
else:
error()
elif (x, a) in dists.keys():
s = dists[(x, a)]
for i in range(len(s) - 1, -1, -1):
if s[i] != 'e':
stack.append(s[i])
else:
error()
count += 1
def main():
# str = input()
str = '#i*i+i#'
print("步骤\t\t符号栈\t\t输入串\t\t\t所用产生式")
masterctrl(str)
if __name__ == '__main__':
main()
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