only print out ast if DEBUG env var is set.

c/mul/main.c

}
int main(int argc, char** argv) {
	int debug_mode = 0;
	if (getenv("DEBUG")) {
		debug_mode = 1;
	}
	mpc_parser_t* Number = mpc_new("number");
	mpc_parser_t* Operator = mpc_new("operator");
	mpc_parser_t* Expr = mpc_new("expr");
		mpc_result_t r;
		if (mpc_parse("<stdin>", input, Lang, &r)) {
			mpc_ast_t* t = r.output;
			mpc_ast_print(t->children[1]);
			if (debug_mode) {
				mpc_ast_print(t->children[1]);
			}
			long result = eval(t->children[1]);
			printf("%li\n", result);
			mpc_ast_delete(r.output);