import os
import tkinter as tk
import tkinter.messagebox
import tkinter.font as tf
zhuizhong = ""
wenfa = {"非左递归文法"}
xi_ = ""
huo = ""
window = tk.Tk()
window.title('消除左递归')
window.minsize(500,500)
#转换坐标显示形式为元组
def getIndex(text, pos):
return tuple(map(int, str.split(text.index(pos), ".")))
def zhijie(x,y):
if not len(y):
pass
else:
if x == y[0]:
wenfa.discard("非左递归文法")
#处理直接左递归
zuobian = y.split('|')
feizhongjie = []
zhongjie = []
for item in zuobian:
if x in item:
item = item[1:]
textt = str(item) + str(x) + "'"
feizhongjie.append(textt)
else:
text = str(item) + str(x) + "'"
zhongjie.append(text)
if not zhongjie:#处理A -> Ax的情况
zhongjie.append(str(x + "'"))
cheng = str(x) + " -> " + "|".join(zhongjie)
zi = str(x) + "'" + " -> " + "|".join(feizhongjie) + "|"
text_output.insert('insert','直接左递归文法','tag1')
text_output.insert('insert','n')
text_output.insert('insert',cheng,'tag2')
text_output.insert('insert','n')
text_output.insert('insert',zi,'tag2')
'''
加上会判断输出非递归产生式，但会导致间接左递归不能删除多余产生式
else:
h ="不变： " + x + " -> " + y
text_output.insert('insert','非左递归文法','tag1')
text_output.insert('insert','n')
text_output.insert('insert',h,'tag2')
'''
text_output.insert('insert','n')
def zhijie2(x,y):
if not len(y):
pass
else:
if x == y[0]:
wenfa.discard("非左递归文法")
#处理直接左递归
zuobian = y.split('|')
feizhongjie = []
zhongjie = []
for item in zuobian:
if x in item:
item = item[1:]
textt = str(item) + str(x) + "'"
feizhongjie.append(textt)
else:
text = str(item) + str(x) + "'"
zhongjie.append(text)
cheng = str(x) + " -> " + "|".join(zhongjie)
zi = str(x) + "'" + " -> " + "|".join(feizhongjie) + "|"
text_output.insert('insert',"间接左递归文法",'tag1')
text_output.insert('insert','n')
text_output.insert('insert',cheng,'tag2')
text_output.insert('insert','n')
text_output.insert('insert',zi,'tag2')
text_output.insert('insert','n')
def tihuan(xk,yi,yk):
yi_you = []
yi_wu =[]
yi_he = ""
yi_wuhe = ""
yi_zhong = ""
yi_feizhong = []
if xk in yi:
yk_replace = yk.split('|')
yi_fenjie = yi.split('|')#将含非终结与不含分开
for ba in yi_fenjie:
if xk in ba:
yi_you.append(ba)
else:
yi_wu.append(ba)
yi_he = "|".join(yi_you)
for item in yk_replace:
yi_zhong = yi_he.replace(xk,item)#替换
yi_feizhong.append(yi_zhong)
yi_wuhe = "|".join(yi_wu)#再合并
global zhuizhong
zhuizhong = "|".join(yi_feizhong) + "|" + yi_wuhe
#点击按钮后执行的函数
def changeString():
text_output.delete('1.0','end')
text = text_input.get('1.0','end')
text_list = list(text.split('n'))#一行一行的拿文法
text_list.pop()
if not text_list[0]:
print(tkinter.messagebox.showerror(title = '出错了！',message='输入不能为空'))
else:
for cfg in text_list:
x,y = cfg.split('->')#将文法左右分开
x = ''.join(x.split())#消除空格
y = ''.join(y.split())
if not (len(x) == 1 and x >= 'A' and x <= 'Z'):
pos = text_input.search(x, '1.0', stopindex="end")
result = tkinter.messagebox.showerror(title = '出错了！',
message='非上下文无关文法!坐标%s'%(getIndex(text_input, pos),))
# 返回值为：ok
print(result)
return 0
else:
zhijie(x,y)
for i in range(len(text_list)):
for k in range(i):
xi,yi = text_list[i].split('->')
xi = ''.join(xi.split())#消除空格
yi = ''.join(yi.split())
xk,yk = text_list[k].split('->')
xk = ''.join(xk.split())#消除空格
yk = ''.join(yk.split())
tihuan(xk,yi,yk)
tihuan(xk,zhuizhong,yk)
global xi_
xi_ = xi
zhijie2(xi_,zhuizhong)
for item in wenfa:
text_output.insert('insert',item,'tag1')
#创建文本输入框和按钮
text_input = tk.Text(window, width=80, height=16)
text_output = tk.Text(window, width=80, height=20)
#简单样式
ft = tf.Font(family='微软雅黑',size=12)
text_output.tag_config("tag1",background="yellow",foreground="red",font=ft)
text_output.tag_config('tag2',font = ft)
#按钮
button = tk.Button(window,text="消除左递归",command=changeString,padx=32,pady=4,bd=4)
text_input.pack()
text_output.pack()
button.pack()
window.mainloop()
做一件事并不难，最难的是没有方向，不知道要做什么；只是感觉时光流逝自己却一点东西都没产出。幸好有具体的题目可供选择，这一次我稍有纠结之后，果断选择文法左递归消除，说实话，我认为这个最简单。
到此这篇关于python实现文法左递归的消除方法的文章就介绍到这了,更多相关python文法左递归消除内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持！
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