===== para_match.l =====

%{
#include <stdio.h>
int cnt1 = 0, cnt2 = 0, cnt3 = 0;
extern FILE *yyin;
%}
%%
\(     { cnt1++; }
\)     { cnt1--; }
\[     { cnt2++; }
\]     { cnt2--; }
\{     { cnt3++; }
\}     { cnt3--; }
[a-zA-Z] {}
\n {
    if (cnt1 == 0 && cnt2 == 0 && cnt3 == 0)
        printf("matching \n");
    else
        printf("not matching \n");

    cnt1 = cnt2 = cnt3 = 0;}
. {}
%%
int main(){
    yyin = fopen("input.txt", "r");
    if (!yyin) {
        perror("Cannot open input.txt");
        return 1;}
    yylex();
    fclose(yyin);
    return 0;
}

===== input.txt =====
(a+b)
(a{)
({})

===== output.txt =====
matching
not matching
matching

===== run =====
nano para_match.l
lex para_match.l
gcc lex.yy.c -o para_match -ll
./para_match