forked from raviraj437/comp
-
Notifications
You must be signed in to change notification settings - Fork 0
/
shift reduce parser.cpp
66 lines (65 loc) · 1.57 KB
/
shift reduce parser.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
#include<bits/stdc++.h>
using namespace std;
/*SHIFT REDUCE PARSER FOR FOLLOWING GRAMMAR
E->2E2
E->3E3
E->4
*/
string LHS[]={"E","E","E"};
string RHS[]={"2E2","3E3","4"};
void print(queue<char> q){
while(q.size()){
cout<<q.front();
q.pop();
}
cout<<"\t\t";
}
int main(){
string ip;
cout<<"Enter the Input String to be parsed"<<endl;
cin>>ip;
queue<char> q;
for(char x:ip)
q.push(x);
q.push('$');
string Stack="$";
cout<<"STACK\tINPUT BUFFER\tPARSING ACTION"<<endl;
bool accept=false;
while((q.size()>1)||(Stack.length()>=2)){
//print output;
cout<<Stack<<"\t";
print(q);
int act=-1;
//can i reduce?
int rule=-1;
for(int i=0;i<3;i++){
size_t found=Stack.rfind(RHS[i]);
if(found!=string::npos){
if(found+RHS[i].length()==Stack.length()){
rule=i;
Stack.replace(found,RHS[i].length(),LHS[i]);
break;
}
}
}
if(rule!=-1){
cout<<"REDUCE USING RULE "<<LHS[rule]<<"->"<<RHS[rule]<<endl;
continue;
}
//can i shift
if(q.size()>1){
Stack=Stack+q.front();
q.pop();
cout<<"SHIFT"<<endl;
continue;
}
break;
}
if(Stack=="$E"&&q.size()==1){
cout<<"ACCEPT"<<endl;
}
else{
cout<<"ERROR! NOT A VALID EXPRESSION"<<endl;
}
return 0;
}