编译原理-语法制导翻译实现计算器

原文链接

任务描述

设计一个文法，匹配合法的计算式，并返回正确计算式的结果。

文法

 

A→BCC→+BC∣−BC∣εB→DEE→∗DE∣/DE∣εD→digit∣(A)A→BCC→+BC∣−BC∣εB→DEE→∗DE∣/DE∣εD→digit∣(A)

 

 

FIRST(A)={digit,(}FIRST(B)={digit,(}FIRST(C)={+,−,ε}FIRST(D)={digit,(}FIRST(E)={∗,/,ε}FOLLOW(A)={$,)}FOLLOW(B)={$,),+,−}FOLLOW(C)={$,)}FOLLOW(D)={$,),∗,/,+,−}FOLLOW(E)={$,),+,−}FIRST(A)={digit,(}FOLLOW(A)={$,)}FIRST(B)={digit,(}FOLLOW(B)={$,),+,−}FIRST(C)={+,−,ε}FOLLOW(C)={$,)}FIRST(D)={digit,(}FOLLOW(D)={$,),∗,/,+,−}FIRST(E)={∗,/,ε}FOLLOW(E)={$,),+,−}

 

LL(1) 预测分析表

 digit()+-*/$
A A→BCA→BC A→BCA→BC            
B B→DEB→DE B→DEB→DE            
C     C→εC→ε C→+BCC→+BC C→−BCC→−BC     C→εC→ε
D D→digitD→digit D→(A)D→(A)            
E     E→εE→ε E→εE→ε E→εE→ε E→∗DEE→∗DE E→/DEE→/DE E→εE→ε

SDD

 产生式语义规则
0) A→BCA→BC
C.inh=B.synA.syn=C.synC.inh=B.synA.syn=C.syn
1) C→+BC1C→+BC1
C1.inh=C.inh+B.synC.syn=C1.synC1.inh=C.inh+B.synC.syn=C1.syn
2) C→−BC1C→−BC1
C1.inh=C.inh−B.synC.syn=C1.synC1.inh=C.inh−B.synC.syn=C1.syn
3) C→εC→ε
C.syn=C.inhC.syn=C.inh
4) B→DEB→DE
E.inh=D.synB.syn=E.synE.inh=D.synB.syn=E.syn
5) E→∗DE1E→∗DE1
E1.inh=E.inh×D.synE.syn=E1.synE1.inh=E.inh×D.synE.syn=E1.syn
6) E→/DE1E→/DE1
E1.inh=E.inh/D.synE.syn=E1.synE1.inh=E.inh/D.synE.syn=E1.syn
7) E→εE→ε
E.syn=E.inhE.syn=E.inh
8) D→digitD→digit
D.syn=digit.lexvalD.syn=digit.lexval
9) D→(A)D→(A) \begin{align} &D.syn = A.syn \end{align*}

程序实现

- 收起代码
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#include <vector>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <exception>
#include <algorithm>
using namespace std;
 
struct node {
int id, syn, inh;
node(int id=0, int syn=0, int inh=0): id(id), syn(syn), inh(inh) {}
};
char key[128];
int M[10][10];
vector<int> v[10];
 
inline int idx(char c) {
return key[c];
}
 
inline void initid() {
memset(key, 0, sizeof key);
 
for(int k='0'; k <= '9'; ++k) key[k] = 1;
key['('] = 2;
key[')'] = 3;
key['+'] = 4;
key['-'] = 5;
key['*'] = 6;
key['/'] = 7;
key['$'] = 8;
 
key['A'] = -1;
key['B'] = -2;
key['C'] = -3;
key['D'] = -4;
key['E'] = -5;
}
 
inline void inittable() {
#define pb push_back
for(int i=0; i < 10; ++i) v[i].clear();
 
v[0].pb(idx('B')); v[0].pb(idx('C')); // A --> BC
v[1].pb(idx('+')); v[1].pb(idx('B')); v[1].pb(idx('C')); // C --> +BC
v[2].pb(idx('-')); v[2].pb(idx('B')); v[2].pb(idx('C')); // C --> -BC
// C --> \varepsilon
v[4].pb(idx('D')); v[4].pb(idx('E')); // B --> DE
v[5].pb(idx('*')); v[5].pb(idx('D')); v[5].pb(idx('E')); // E --> *DE
v[6].pb(idx('/')); v[6].pb(idx('D')); v[6].pb(idx('E')); // E --> /DE
// E --> \varepsilon
v[8].pb(idx('0')); // D --> digit
v[9].pb(idx('(')); v[9].pb(idx('A')); v[9].pb(idx(')')); // D --> (A)
 
// for(int i=0; i < 10; ++i) reverse(v[i].begin(), v[i].end());
#undef pb
 
memset(M, -1, sizeof M);
M[1][1] = 0; M[1][2] = 0;
M[2][1] = 4; M[2][2] = 4;
M[3][3] = 3; M[3][4] = 1; M[3][5] = 2; M[3][8] = 3;
M[4][1] = 8; M[4][2] = 9;
M[5][3] = 7; M[5][4] = 7; M[5][5] = 7; M[5][6] = 5; M[5][7] = 6; M[5][8] = 7;
}
 
int getnum(const char*& s) {
int num = 0;
for(; isdigit(*s); ++s)
num = num*10 + *s-'0';
return num;
}
 
const int endsym = idx('$');
void work(const char* &s, node& sy, int cur) {
int id = idx(*s);
if( !id ) throw "不识别的符号";
 
if( sy.id != endsym ) {
if( sy.id == id ) {
if( id == 1 ) {
sy.syn = getnum(s);
} else ++s;
return;
}
if( sy.id > 0 ) throw "error!";
int Mid = M[-sy.id][id];
if( Mid < 0 ) throw "error!";
node sym[4];
for(int i=0; i < v[Mid].size(); ++i)
sym[i].id = v[Mid][i];
if( v[Mid].size() )work(s, sym[0], cur+1);
switch( Mid ) {
case 0:
case 4:
sym[1].inh = sym[0].syn;
work(s, sym[1], cur+1);
sy.syn = sym[1].syn;
break; // A --> BC 或 B --> DE
case 1:
work(s, sym[1], cur+1);
sym[2].inh = sy.inh+sym[1].syn;
work(s, sym[2], cur+1);
sy.syn = sym[2].syn;
break; // C --> +BC
case 2:
work(s, sym[1], cur+1);
sym[2].inh = sy.inh-sym[1].syn;
work(s, sym[2], cur+1);
sy.syn = sym[2].syn;
break; // C --> -BC
case 3:
case 7:
sy.syn = sy.inh;
break; // C --> \epsilon 或 E --> \epsilon
case 5:
work(s, sym[1], cur+1);
sym[2].inh = sy.inh*sym[1].syn;
work(s, sym[2], cur+1);
sy.syn = sym[2].syn;
break; // E --> *DE
case 6:
work(s, sym[1], cur+1);
sym[2].inh = sy.inh/sym[1].syn;
work(s, sym[2], cur+1);
sy.syn = sym[2].syn;
break; // E --> /DE
case 8: sy.syn = sym[0].syn;
break; // D --> digit
case 9:
work(s, sym[1], cur+1);
sy.syn = sym[1].syn;
work(s, sym[2], cur+1);
break; // D --> (A)
}
}
if( cur == 0 ) throw sy.syn;
}
 
int main()
{
string in;
string coin;
initid();
inittable();
while( getline(cin, in) ) {
in.push_back('$');
int len = in.length();
const char* s = in.c_str();
coin.clear();
for(int i=0; i < len; ++i)
if( s[i] !=' ' && s[i] != '\t' && s[i] != '\n' )
coin.push_back(s[i]);
coin.push_back('\0');
/* 以上去除空格 */
 
try {
node sy = node(idx('A'));
s = coin.c_str();
work(s, sy, 0);
}
catch(const char* str) {
puts(str);
}
catch(int ans) {
for(int i=0; i < len-1; ++i) putchar(in[i]);
printf(" = %d\n", ans);
printf("succuss!\n");
}
}
return 0;
}
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posted @ 2017-05-30 18:07  天涯海角路  阅读(512)  评论(0)    收藏  举报