Experiment two recursive-descent parsing - Job 12

First, the purpose of the experiment:

The use of C language compiled recursive descent parsing procedures, and simple language parsing.

The preparation of a recursive descent parser, syntax checking and realize the structure of the word lexical analysis program provided by sequence analysis.

 

Second, the experimental principle

Each nonterminal symbol corresponds to a subroutine.

This subroutine is determined according to a next input symbol (SELECT sets) which are processed in a production, then the right end of the production according to:

• Each encounter a terminator, it is determined whether the current read word matches the terminator, if matched, then the next word is read to continue the analysis; do not match, an error process is performed
• Each encounter a nonterminal, the appropriate subroutine is called

 

Third, the experiment asked for clarification

Enter the word string to "#" end if the grammar is correct sentences, the output success information, print "success", otherwise output "error", and pointed out grammatical errors of the type and location.

E.g:

Input begin a: = 9; x: = 2 * 3; b: = a + x end #

Output success

Input x: = a + b * c end #

Output 'end' error

 

Fourth, the experimental procedures

      1. Grammar of the language to be analyzed (refer to P90)

      2. Grammar to be expressed, at least comprising

- Statement

-condition

-expression

3. eliminate left recursion

4. Extract the left common factor

5. SELECT set computing

6. LL (1) grammar is determined

7. recursive descent parser

 

Fifth, the experimental source:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

char PROG [] = " A + B * # 20 is " , token [ 20 is ];         // Block, word symbols 
char CH;
 int SYN, P, m, n-, SUM;             // word SYN symbol type, integer SUM 
char rwtab * [ . 6 ] = { " the begin " , " IF " , " the then " , " the while " , " do " , " End " };
 
void E();
void T();
void E1();
void T1();
void F();
void error();

void scanner()
{
    for (n=0;n<20;n++) token[n]=NULL;
    m=0;
    sum=0;
    ch=prog[p++];
    while (ch==' ') {ch=prog[p++];}
    if (ch>='a' && ch<='z')
        {while (ch>='a' && ch<='z'||ch>='0' && ch<='9')
            {
                token[m++]=ch;
                CH = prog [i ++ ];
            }
                    
         syn=10;p--;
         for(n=0;n<6;n++)
             if(strcmp(token,rwtab[n])==0) {syn=n+1;break;}
        }
    else
        if(ch>='0' && ch<='9')
            {while (ch>='0' && ch<='9')
                {
                    sum=sum*10+(ch-'0');
                    CH = prog [i ++ ];
                }
                
             syn = 11 ; p-- ;
            }
        else    
            switch(ch)
            {
                case '<': token[m++]=ch;
                          ch=prog[p++];
                          if (ch=='>') {syn=21;token[m++]=ch;}
                          else if (ch=='='){syn=22;token[m++]=ch;}
                              else {syn=20;p--;}
                          break;
                          
                case '>': m=0; token[m++]=ch;
                          ch=prog[p++];
                          if (ch=='=') {syn=24;token[m++]=ch;}
                          else {syn=23;p--;}
                          break;    
                          
                case ':': m=0; token[m++]=ch;
                          ch=prog[p++];
                          if (ch=='=') {syn=18;token[m++]=ch;}
                          else {syn=17;p--;}
                          break;
                          
                case '+': syn=13;token[0]=ch;break;
                case '-': syn=14;token[0]=ch;break;    
                case '*': syn=15;token[0]=ch;break;    
                case '/': syn=16;token[0]=ch;break;    
                case '=': syn=25;token[0]=ch;break;
                case ';': syn=26;token[0]=ch;break;    
                case '(': syn=27;token[0]=ch;break;    
                case ')': syn=28;token[0]=ch;break;    
                case '#': syn=0; token[0]=ch;break;
                default : syn=-1;token[0]=ch;                
            }
}

void E()
{
    T();
    E1 ();
}

void E1()
{
    if (syn==13) {
        scanner();
        T();
        E1 ();
    }
    else  if (syn == 0 || view == 28 ) {
    }
    else
        error();
} 

void T()
{
    F();
    T1 ();    
}

void T1()
{
    if(syn==15){
        scanner();
        F();
        T1 ();
    }
    else clauses  the if (syn == 0 || syn == 28 || syn == 13 ) {
    }
    else
        error();
}

void F()
{
    if (syn==27){
        scanner();
        E();
        if (syn==28)
            scanner();
        else
            error();
        }
    else  if (syn == 11 || view == 10 )
        scanner();
    else
        error();
}

void error()
{
    the printf ( " \ n-(% S, Error)! " , token);
}

main()
{
    scanner();
    E();
}