fix memory leak

Makefile

 SOURCES := $(wildcard library/*.c) $(wildcard src/*.c)
 
 bin/eval: $(SOURCES)
-	clang $^ -g -Iinclude -fsanitize=address,undefined -lreadline -o bin/eval
+	clang $^ -g -Iinclude -fsanitize=address,undefined,leak -lreadline -o bin/eval
 
 clean:
 	rm -f bin/*

src/main.c

@@ -11,6 +11,10 @@ int main(int argc, char *argv[]) {
     char *temp = readline("expr> ");
     
     do {
+        if (!strcmp(temp, "exit") || !strcmp(temp, "quit")) {
+            free(temp);
+            return 0;
+        }
         add_history(temp);
         //expression_t *expr = expression_cfold(expression_parse(temp));
         expression_t *expr = expression_parse(temp);