Earley 算法出错

问题描述

我正在尝试实现用于解析语法的 Earley 算法，但是我一定做错了什么，因为在图表中的第一个条目之后，它没有通过输入字符串的其余部分。

我的测试语法如下：
S -> aXbX | bXaX
X -> aXbX | bXaX |厄普西隆
S 和 X 是非终结符； a 和 b 是终端。

我想检查它是否被语法接受的字符串是：'abba'。

这是我的代码：

rules = {
    "S": [
        ['aXbX'],['bXaX'],],"X" : [
        ['aXbX'],['']
    ]
}

def predictor(rule,state):
    if rule["right"][rule["dot"]].isupper(): # NON-TERMINAL
        return [{
            "left": rule["right"][rule["dot"]],"right": right,"dot": 0,"op": "PREDICTOR","completor": []
        } for right in rules[rule["right"][rule["dot"]]]] 
    else:
        return []


def scanner(rule,next_input):
    # TERMINAL
    if rule["right"][rule["dot"]].islower() and next_input in rules[rule["right"][rule["dot"]]]:
        print('scanner')
        return [{
            "left": rule["right"][rule["dot"]],"right": [next_input],"dot": 1,"op": "SCANNER","completor": []
        }] 
    else:
        return []

def completor(rule,charts):
    if rule["dot"] == len(rule["right"]):
        print('completor')
        return list(map(
            lambda filter_rule: {
                "left": filter_rule["left"],"right": filter_rule["right"],"dot": filter_rule["dot"] + 1,"op": "COMPLetoR","completor": [rule] + filter_rule["completor"]
            },filter(
                lambda p_rule: p_rule["dot"] < len(p_rule["right"]) and rule["left"] == p_rule["right"][p_rule["dot"]],charts[rule["state"]]
            )
        )) 
    else:
        return []

input_string = 'abba'
input_arr = [char for char in input_string] + ['']
charts = [[{
    "left": "S'","right": ["S"],"op": "-","completor": []
}]]

for curr_state in range(len(input_arr)):

    curr_chart = charts[curr_state]
    next_chart = []

    for curr_rule in curr_chart:
        if curr_rule["dot"] < len(curr_rule["right"]): # not finished
            curr_chart += [i for i in predictor(curr_rule,curr_state) if i not in curr_chart]
            next_chart += [i for i in scanner(curr_rule,input_arr[curr_state]) if i not in next_chart]
        else:
            print('else')
            curr_chart += [i for i in completor(curr_rule,charts) if i not in curr_chart]

    charts.append(next_chart)

def print_charts(charts,inp):
    for chart_no,chart in zip(range(len(charts)),charts):
        print("\t{}".format("S" + str(chart_no)))
        print("\t\n".join(map(
            lambda x: "\t{} --> {},{} {}".format(
                x["left"],"".join(x["right"][:x["dot"]] + ["."] + x["right"][x["dot"]:]),str(chart_no) + ',',x["op"]
            ),chart
        )))
        print()
print_charts(charts[:-1],input_arr)

这是我得到的输出（对于状态 1 到 4，我应该得到 5 到 9 个条目）：
S0
S' --> .S,-
S --> .aXbX,预测器
S --> .bXaX,预测器

S1

S2

S3

S4

解决方法

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