Flex + Lemon problems

grammar.y

%include {
    #include <assert.h>
    #include <stdlib.h>
}

%token_type { char* }

%syntax_error { fprintf(stderr, "Syntax error.\n"); }
%stack_overflow { fprintf(stderr, "Stack overflow.\n"); }
%parse_failure { fprintf(stderr, "Parse failed.\n"); }

%type top { int }
%type prog { int }
%type sexp_list { int }
%type sexp { int }
%type atom { int }

top(T)         ::= prog(P). { T = P; printf("AST=%d.\n", T); }

prog(P)        ::= sexp_list(L). { P = L; }
prog(P)        ::= . { P = -1; }

sexp_list(L)   ::= sexp(S) sexp_list(L1). { L = S + L1; }
sexp_list(L)   ::= sexp(S). { L = S; }

sexp(S)        ::= atom(A). { S = A; }

atom(A)        ::= INT(V). { A = atoi(V); printf("found int of %s.\n", V); }

lexer.l

%top{
    #include "grammar.h"
}

%option reentrant warn
%option noyywrap noinput nounput

%%

[0-9]+          { return INT; }

%%

main.c

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

#include "grammar.h"
#include "lexer.h"

// Declarations for the lemon parser.
void* ParseAlloc(void* (*allocProc)(size_t));
void Parse(void*, int, char*);
void ParseFree(void*, void(*freeProc)(void*));

int main() {
    yyscan_t lexer;
    void* parser = ParseAlloc(malloc);
    int token;

    yylex_init(&lexer);
    yyset_in(stdin, lexer);

    do {
        token = yylex(lexer);
        Parse(parser, token, yyget_text(lexer));
    } while(token != 0);

    yylex_destroy(lexer);
    ParseFree(parser, free);
    return 0;
}