%{
    #include "y.tab.h"
    #include <stdlib.h>
%}

%%
[0-9]+      {yylval = atoi(yytext); return INTEGER;}
[+]         return PLUS;
[n]        return NL;
[ t]       ;       /* skip whitespace */
.           {printf("Unknown character '%c'n", yytext[0]); return 0;}
%%

int yywrap(void) {
    return 1;
}

%{
    #include <stdio.h>
    int yylex(void);
    void yyerror(char *);
%}

%token INTEGER PLUS NL
%left PLUS MINUS

%%

prog:   prog expr NL                { printf("%dn", $2); }
        |
        ;
expr:   INTEGER                     { $$ = $1; }
        | expr PLUS expr            { $$ = $1 + $3; }
        ;
%%

void yyerror(char *s) {
    fprintf(stderr, "%sn", s);
}

int main(void) {
    yyparse();
    return 0;
}

bison -y -d badd.y
flex badd.l
gcc y.tab.c lex.yy.c -o badd.exe

%{
    #include "ladd.h"
    #include <stdlib.h>
    extern int yylval;
%}

%%
[0-9]+      {yylval = atoi(yytext); return INTEGER;}
[+]         return PLUS;
[n]        return NL;
[ t]       ;       /* skip whitespace */
.           {printf("Unknown character '%c'n", yytext[0]); return 0;}
%%

int yywrap(void) {
    return 1;
}

%include { #include <assert.h> }
%syntax_error { printf("Lemon syntax errorn"); }
%token_type {int}
%left PLUS MINUS .

start   ::= prog .

prog    ::= prog expr(a) NL .           { printf("%dn", a); }
prog    ::= .

expr(a) ::= INTEGER(b) .                { a = b; }
expr(a) ::= expr(b) PLUS expr(c) .      { a = b + c; }

lemon ladd.y
flex ladd.l
gcc main.c ladd.c lex.yy.c -o ladd.exe

start   ::= prog .

prog    ::= prog print NL .
prog    ::= .

print   ::= expr(a) .         { printf("%dn", a); }