Accelerated C++ 7 generate sentence

最新推荐文章于 2018-10-21 15:05:04 发布

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本文介绍了一个基于文本的语法生成器，该生成器能够从定义好的文法文件中读取规则并随机生成符合这些规则的句子。通过使用C++实现，文章详细展示了如何解析文法文件、构建语法树以及生成句子的过程。

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split.h
see Note 6
grammar.txt

<noun>  cat
<noun>  dog
<noun>  table
<noun-phrase>   <noun>
<noun-phrase>   <adjective> <noun-phrase>
<adjective> large
<adjective> brown
<adjective> absurd
<verb>  jumps
<verb>  sits
<location>  on the stairs
<location>  under the sky
<location>  wherever it wants
<sentence>  the <noun-phrase> <verb> <location>

main.cpp

#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdexcept>
#include <fstream>
#include "split.h"

using std::cout; using std::endl; using std::domain_error;
using std::string; using std::vector; using std::istream;
using std::map; using std::ifstream;    using std::logic_error;
using std::cerr;

typedef vector<string> Rule;
typedef vector<Rule> Rule_collection;
typedef map<string, Rule_collection> Grammar;

Grammar read_grammar(ifstream& infile) {
    Grammar ret;
    string line;

    while(getline(infile, line)) {
        vector<string> entry = split(line);

        if(!entry.empty()) {
            Rule rules(entry.begin() + 1, entry.end());
            ret[entry[0]].push_back(rules);
        }
    }
    return ret;
}

int nrand(int n) {
    if (n < 0 || n > RAND_MAX)
        throw domain_error("Argument to nrand is out of range");
    const int bucket_size = RAND_MAX / n;
    int r;

    do r = rand() / bucket_size;
    while (r > n);

    return r;
}

bool bracketed(const string& s) {
    return s[0] == '<' && s[s.size() - 1] == '>';
}



void gen_aux(const Grammar& g, const string& s, vector<string>& v) {

    if (bracketed(s)){
        Grammar::const_iterator it = g.find(s);
        if (it == g.end())
            throw logic_error("empty error");

        const Rule_collection& rc = it->second;
        const Rule r = rc[nrand(rc.size())];

        for (Rule::size_type i = 0; i != r.size(); ++i)
            gen_aux(g, r[i], v);
    } else 
        v.push_back(s);

}

vector<string> gen_sentence(const Grammar& g) {
    vector<string> ret;
    gen_aux(g, "<sentence>", ret);

    return ret;
}

int main() {

    string ifile = "grammar.txt";

    ifstream infile(ifile.c_str());

    // check that the open succeede
    if (!infile) {
        cerr << "error: unable to open input file: "
            << ifile << endl;
        return -1;
    }

    // generate the sentence
    Grammar g = read_grammar(infile);
    vector<string> sentence = gen_sentence(g);

    // write the first word, if any
    vector<string>::const_iterator it = sentence.begin();
    if(!sentence.empty()) {
        cout << *it;
        ++it;
    }

    // write the rest of the word, each preceded by a space
    while (it != sentence.end()) {
        cout << " " << *it;
        ++it;
    }

    cout << endl;
    return 0;
}