diff --git a/build/gcc/Makefile b/build/gcc/Makefile
index e3a39c0..36cdabe 100644
--- a/build/gcc/Makefile
+++ b/build/gcc/Makefile
@@ -1,6 +1,9 @@
 CC=gcc
-CFLAGS_D=-std=gnu89 -fsigned-char -Wall -Wextra -Wno-unused-parameter -Wno-overlength-strings -pedantic -O0 -g2
-CFLAGS_R=-std=gnu89 -fsigned-char -Wall -Wextra -Wno-unused-parameter -Wno-overlength-strings -pedantic -O2 -DNDEBUG
+CFLAGS_0=-std=gnu89 -fsigned-char -Wall -Wextra -Wno-overlength-strings -pedantic
+CFLAGS_D=        $(CFLAGS_0) -Wno-unused-parameter -O0 -g2
+CFLAGS_EXAMPLE_D=$(CFLAGS_0)                       -O0 -g2
+CFLAGS_R=        $(CFLAGS_0) -Wno-unused-parameter -O2 -DNDEBUG
+CFLAGS_EXAMPLE_R=$(CFLAGS_0)                       -O2 -DNDEBUG
 LDFLAGS_D=
 LDFLAGS_R=
 
diff --git a/src/packcc.c b/src/packcc.c
index 3ce3b28..d73fa6c 100644
--- a/src/packcc.c
+++ b/src/packcc.c
@@ -2898,9 +2898,9 @@ static code_reach_t generate_quantifying_code(generate_t *gen, const node_t *exp
                 indent += 4;
             }
             stream__write_characters(gen->stream, ' ', indent);
-            stream__puts(gen->stream, "const size_t p = ctx->cur;\n");
+            stream__puts(gen->stream, "const size_t p MARK_VAR_AS_USED = ctx->cur;\n");
             stream__write_characters(gen->stream, ' ', indent);
-            stream__puts(gen->stream, "const size_t n = chunk->thunks.len;\n");
+            stream__puts(gen->stream, "const size_t n MARK_VAR_AS_USED = chunk->thunks.len;\n");
             {
                 const int l = ++gen->label;
                 if (generate_code(gen, expr, l, indent, FALSE) != CODE_REACH__ALWAYS_SUCCEED) {
@@ -3024,9 +3024,9 @@ static code_reach_t generate_alternative_code(generate_t *gen, const node_array_
         indent += 4;
     }
     stream__write_characters(gen->stream, ' ', indent);
-    stream__puts(gen->stream, "const size_t p = ctx->cur;\n");
+    stream__puts(gen->stream, "const size_t p MARK_VAR_AS_USED = ctx->cur;\n");
     stream__write_characters(gen->stream, ' ', indent);
-    stream__puts(gen->stream, "const size_t n = chunk->thunks.len;\n");
+    stream__puts(gen->stream, "const size_t n MARK_VAR_AS_USED = chunk->thunks.len;\n");
     for (i = 0; i < nodes->len; i++) {
         const bool_t c = (i + 1 < nodes->len) ? TRUE : FALSE;
         const int l = ++gen->label;
@@ -3365,6 +3365,11 @@ static bool_t generate(context_t *ctx) {
             "#else\n"
             "#define MARK_FUNC_AS_USED __attribute__((__unused__))\n"
             "#endif\n"
+            "#ifdef _MSC_VER\n"
+            "#define MARK_VAR_AS_USED\n"
+            "#else\n"
+            "#define MARK_VAR_AS_USED __attribute__((__unused__))\n"
+            "#endif\n"
             "\n"
             "#ifndef PCC_BUFFER_MIN_SIZE\n"
             "#define PCC_BUFFER_MIN_SIZE 256\n"
@@ -3666,7 +3671,7 @@ static bool_t generate(context_t *ctx) {
             "#define PCC_DEBUG(auxil, event, rule, level, pos, buffer, length) ((void)0)\n"
             "#endif /* !PCC_DEBUG */\n"
             "\n"
-            "static char *pcc_strndup_e(pcc_auxil_t auxil, const char *str, size_t len) {\n"
+            "static char *pcc_strndup_e(pcc_auxil_t auxil MARK_VAR_AS_USED, const char *str, size_t len) {\n"
             "    const size_t m = strnlen(str, len);\n"
             "    char *const s = (char *)PCC_MALLOC(auxil, m + 1);\n"
             "    memcpy(s, str, m);\n"
@@ -3677,13 +3682,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_char_array__init(pcc_auxil_t auxil, pcc_char_array_t *array) {\n"
+            "static void pcc_char_array__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_char_array_t *array) {\n"
             "    array->len = 0;\n"
             "    array->max = 0;\n"
             "    array->buf = NULL;\n"
             "}\n"
             "\n"
-            "static void pcc_char_array__add(pcc_auxil_t auxil, pcc_char_array_t *array, char ch) {\n"
+            "static void pcc_char_array__add(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_char_array_t *array, char ch) {\n"
             "    if (array->max <= array->len) {\n"
             "        const size_t n = array->len + 1;\n"
             "        size_t m = array->max;\n"
@@ -3696,21 +3701,21 @@ static bool_t generate(context_t *ctx) {
             "    array->buf[array->len++] = ch;\n"
             "}\n"
             "\n"
-            "static void pcc_char_array__term(pcc_auxil_t auxil, pcc_char_array_t *array) {\n"
+            "static void pcc_char_array__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_char_array_t *array) {\n"
             "    PCC_FREE(auxil, array->buf);\n"
             "}\n"
             "\n"
         );
         stream__puts(
             &sstream,
-            "static void pcc_value_table__init(pcc_auxil_t auxil, pcc_value_table_t *table) {\n"
+            "static void pcc_value_table__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_table_t *table) {\n"
             "    table->len = 0;\n"
             "    table->max = 0;\n"
             "    table->buf = NULL;\n"
             "}\n"
             "\n"
             "MARK_FUNC_AS_USED\n"
-            "static void pcc_value_table__resize(pcc_auxil_t auxil, pcc_value_table_t *table, size_t len) {\n"
+            "static void pcc_value_table__resize(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_table_t *table, size_t len) {\n"
             "    if (table->max < len) {\n"
             "        size_t m = table->max;\n"
             "        if (m == 0) m = PCC_ARRAY_MIN_SIZE;\n"
@@ -3723,24 +3728,24 @@ static bool_t generate(context_t *ctx) {
             "}\n"
             "\n"
             "MARK_FUNC_AS_USED\n"
-            "static void pcc_value_table__clear(pcc_auxil_t auxil, pcc_value_table_t *table) {\n"
+            "static void pcc_value_table__clear(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_table_t *table) {\n"
             "    memset(table->buf, 0, sizeof(pcc_value_t) * table->len);\n"
             "}\n"
             "\n"
-            "static void pcc_value_table__term(pcc_auxil_t auxil, pcc_value_table_t *table) {\n"
+            "static void pcc_value_table__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_table_t *table) {\n"
             "    PCC_FREE(auxil, table->buf);\n"
             "}\n"
             "\n"
         );
         stream__puts(
             &sstream,
-            "static void pcc_value_refer_table__init(pcc_auxil_t auxil, pcc_value_refer_table_t *table) {\n"
+            "static void pcc_value_refer_table__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_refer_table_t *table) {\n"
             "    table->len = 0;\n"
             "    table->max = 0;\n"
             "    table->buf = NULL;\n"
             "}\n"
             "\n"
-            "static void pcc_value_refer_table__resize(pcc_auxil_t auxil, pcc_value_refer_table_t *table, size_t len) {\n"
+            "static void pcc_value_refer_table__resize(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_refer_table_t *table, size_t len) {\n"
             "    size_t i;\n"
             "    if (table->max < len) {\n"
             "        size_t m = table->max;\n"
@@ -3754,21 +3759,21 @@ static bool_t generate(context_t *ctx) {
             "    table->len = len;\n"
             "}\n"
             "\n"
-            "static void pcc_value_refer_table__term(pcc_auxil_t auxil, pcc_value_refer_table_t *table) {\n"
+            "static void pcc_value_refer_table__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_value_refer_table_t *table) {\n"
             "    PCC_FREE(auxil, table->buf);\n"
             "}\n"
             "\n"
         );
         stream__puts(
             &sstream,
-            "static void pcc_capture_table__init(pcc_auxil_t auxil, pcc_capture_table_t *table) {\n"
+            "static void pcc_capture_table__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_table_t *table) {\n"
             "    table->len = 0;\n"
             "    table->max = 0;\n"
             "    table->buf = NULL;\n"
             "}\n"
             "\n"
             "MARK_FUNC_AS_USED\n"
-            "static void pcc_capture_table__resize(pcc_auxil_t auxil, pcc_capture_table_t *table, size_t len) {\n"
+            "static void pcc_capture_table__resize(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_table_t *table, size_t len) {\n"
             "    size_t i;\n"
             "    for (i = len; i < table->len; i++) PCC_FREE(auxil, table->buf[i].string);\n"
             "    if (table->max < len) {\n"
@@ -3787,7 +3792,7 @@ static bool_t generate(context_t *ctx) {
             "    table->len = len;\n"
             "}\n"
             "\n"
-            "static void pcc_capture_table__term(pcc_auxil_t auxil, pcc_capture_table_t *table) {\n"
+            "static void pcc_capture_table__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_table_t *table) {\n"
             "    while (table->len > 0) {\n"
             "        table->len--;\n"
             "        PCC_FREE(auxil, table->buf[table->len].string);\n"
@@ -3798,13 +3803,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_capture_const_table__init(pcc_auxil_t auxil, pcc_capture_const_table_t *table) {\n"
+            "static void pcc_capture_const_table__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_const_table_t *table) {\n"
             "    table->len = 0;\n"
             "    table->max = 0;\n"
             "    table->buf = NULL;\n"
             "}\n"
             "\n"
-            "static void pcc_capture_const_table__resize(pcc_auxil_t auxil, pcc_capture_const_table_t *table, size_t len) {\n"
+            "static void pcc_capture_const_table__resize(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_const_table_t *table, size_t len) {\n"
             "    size_t i;\n"
             "    if (table->max < len) {\n"
             "        size_t m = table->max;\n"
@@ -3818,7 +3823,7 @@ static bool_t generate(context_t *ctx) {
             "    table->len = len;\n"
             "}\n"
             "\n"
-            "static void pcc_capture_const_table__term(pcc_auxil_t auxil, pcc_capture_const_table_t *table) {\n"
+            "static void pcc_capture_const_table__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_capture_const_table_t *table) {\n"
             "    PCC_FREE(auxil, (void *)table->buf);\n"
             "}\n"
             "\n"
@@ -3840,7 +3845,7 @@ static bool_t generate(context_t *ctx) {
             "    return thunk;\n"
             "}\n"
             "\n"
-            "static pcc_thunk_t *pcc_thunk__create_node(pcc_auxil_t auxil, const pcc_thunk_array_t *thunks, pcc_value_t *value) {\n"
+            "static pcc_thunk_t *pcc_thunk__create_node(pcc_auxil_t auxil MARK_VAR_AS_USED, const pcc_thunk_array_t *thunks, pcc_value_t *value) {\n"
             "    pcc_thunk_t *const thunk = (pcc_thunk_t *)PCC_MALLOC(auxil, sizeof(pcc_thunk_t));\n"
             "    thunk->type = PCC_THUNK_NODE;\n"
             "    thunk->data.node.thunks = thunks;\n"
@@ -3867,13 +3872,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_thunk_array__init(pcc_auxil_t auxil, pcc_thunk_array_t *array) {\n"
+            "static void pcc_thunk_array__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_thunk_array_t *array) {\n"
             "    array->len = 0;\n"
             "    array->max = 0;\n"
             "    array->buf = NULL;\n"
             "}\n"
             "\n"
-            "static void pcc_thunk_array__add(pcc_auxil_t auxil, pcc_thunk_array_t *array, pcc_thunk_t *thunk) {\n"
+            "static void pcc_thunk_array__add(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_thunk_array_t *array, pcc_thunk_t *thunk) {\n"
             "    if (array->max <= array->len) {\n"
             "        const size_t n = array->len + 1;\n"
             "        size_t m = array->max;\n"
@@ -3904,13 +3909,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_memory_recycler__init(pcc_auxil_t auxil, pcc_memory_recycler_t *recycler, size_t element_size) {\n"
+            "static void pcc_memory_recycler__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_memory_recycler_t *recycler, size_t element_size) {\n"
             "    recycler->pool_list = NULL;\n"
             "    recycler->entry_list = NULL;\n"
             "    recycler->element_size = element_size;\n"
             "}\n"
             "\n"
-            "static void *pcc_memory_recycler__supply(pcc_auxil_t auxil, pcc_memory_recycler_t *recycler) {\n"
+            "static void *pcc_memory_recycler__supply(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_memory_recycler_t *recycler) {\n"
             "    if (recycler->entry_list) {\n"
             "        pcc_memory_entry_t *const tmp = recycler->entry_list;\n"
             "        recycler->entry_list = tmp->next;\n"
@@ -3936,13 +3941,13 @@ static bool_t generate(context_t *ctx) {
             "    return (char *)recycler->pool_list + sizeof(pcc_memory_pool_t) + recycler->element_size * recycler->pool_list->unused;\n"
             "}\n"
             "\n"
-            "static void pcc_memory_recycler__recycle(pcc_auxil_t auxil, pcc_memory_recycler_t *recycler, void *ptr) {\n"
+            "static void pcc_memory_recycler__recycle(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_memory_recycler_t *recycler, void *ptr) {\n"
             "    pcc_memory_entry_t *const tmp = (pcc_memory_entry_t *)ptr;\n"
             "    tmp->next = recycler->entry_list;\n"
             "    recycler->entry_list = tmp;\n"
             "}\n"
             "\n"
-            "static void pcc_memory_recycler__term(pcc_auxil_t auxil, pcc_memory_recycler_t *recycler) {\n"
+            "static void pcc_memory_recycler__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_memory_recycler_t *recycler) {\n"
             "    while (recycler->pool_list) {\n"
             "        pcc_memory_pool_t *const tmp = recycler->pool_list;\n"
             "        recycler->pool_list = tmp->next;\n"
@@ -3974,13 +3979,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_rule_set__init(pcc_auxil_t auxil, pcc_rule_set_t *set) {\n"
+            "static void pcc_rule_set__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_rule_set_t *set) {\n"
             "    set->len = 0;\n"
             "    set->max = 0;\n"
             "    set->buf = NULL;\n"
             "}\n"
             "\n"
-            "static size_t pcc_rule_set__index(pcc_auxil_t auxil, const pcc_rule_set_t *set, pcc_rule_t rule) {\n"
+            "static size_t pcc_rule_set__index(pcc_auxil_t auxil MARK_VAR_AS_USED, const pcc_rule_set_t *set, pcc_rule_t rule) {\n"
             "    size_t i;\n"
             "    for (i = 0; i < set->len; i++) {\n"
             "        if (set->buf[i] == rule) return i;\n"
@@ -4011,7 +4016,7 @@ static bool_t generate(context_t *ctx) {
             "    return PCC_TRUE;\n"
             "}\n"
             "\n"
-            "static void pcc_rule_set__clear(pcc_auxil_t auxil, pcc_rule_set_t *set) {\n"
+            "static void pcc_rule_set__clear(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_rule_set_t *set) {\n"
             "    set->len = 0;\n"
             "}\n"
             "\n"
@@ -4023,7 +4028,7 @@ static bool_t generate(context_t *ctx) {
             "    }\n"
             "}\n"
             "\n"
-            "static void pcc_rule_set__term(pcc_auxil_t auxil, pcc_rule_set_t *set) {\n"
+            "static void pcc_rule_set__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_rule_set_t *set) {\n"
             "    PCC_FREE(auxil, set->buf);\n"
             "}\n"
             "\n"
@@ -4110,13 +4115,13 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_lr_memo_map__init(pcc_auxil_t auxil, pcc_lr_memo_map_t *map) {\n"
+            "static void pcc_lr_memo_map__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_memo_map_t *map) {\n"
             "    map->len = 0;\n"
             "    map->max = 0;\n"
             "    map->buf = NULL;\n"
             "}\n"
             "\n"
-            "static size_t pcc_lr_memo_map__index(pcc_context_t *ctx, pcc_lr_memo_map_t *map, pcc_rule_t rule) {\n"
+            "static size_t pcc_lr_memo_map__index(pcc_context_t *ctx MARK_VAR_AS_USED, pcc_lr_memo_map_t *map, pcc_rule_t rule) {\n"
             "    size_t i;\n"
             "    for (i = 0; i < map->len; i++) {\n"
             "        if (map->buf[i].rule == rule) return i;\n"
@@ -4182,7 +4187,7 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static void pcc_lr_table__init(pcc_auxil_t auxil, pcc_lr_table_t *table) {\n"
+            "static void pcc_lr_table__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_table_t *table) {\n"
             "    table->ofs = 0;\n"
             "    table->len = 0;\n"
             "    table->max = 0;\n"
@@ -4234,7 +4239,7 @@ static bool_t generate(context_t *ctx) {
             "    table->buf[index]->hold_a = answer;\n"
             "}\n"
             "\n"
-            "static pcc_lr_head_t *pcc_lr_table__get_head(pcc_context_t *ctx, pcc_lr_table_t *table, size_t index) {\n"
+            "static pcc_lr_head_t *pcc_lr_table__get_head(pcc_context_t *ctx MARK_VAR_AS_USED, pcc_lr_table_t *table, size_t index) {\n"
             "    index += table->ofs;\n"
             "    if (index >= table->len || table->buf[index] == NULL) return NULL;\n"
             "    return table->buf[index]->head;\n"
@@ -4268,7 +4273,7 @@ static bool_t generate(context_t *ctx) {
         );
         stream__puts(
             &sstream,
-            "static pcc_lr_entry_t *pcc_lr_entry__create(pcc_auxil_t auxil, pcc_rule_t rule) {\n"
+            "static pcc_lr_entry_t *pcc_lr_entry__create(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_rule_t rule) {\n"
             "    pcc_lr_entry_t *const lr = (pcc_lr_entry_t *)PCC_MALLOC(auxil, sizeof(pcc_lr_entry_t));\n"
             "    lr->rule = rule;\n"
             "    lr->seed = NULL;\n"
@@ -4276,20 +4281,20 @@ static bool_t generate(context_t *ctx) {
             "    return lr;\n"
             "}\n"
             "\n"
-            "static void pcc_lr_entry__destroy(pcc_auxil_t auxil, pcc_lr_entry_t *lr) {\n"
+            "static void pcc_lr_entry__destroy(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_entry_t *lr) {\n"
             "    PCC_FREE(auxil, lr);\n"
             "}\n"
             "\n"
         );
         stream__puts(
             &sstream,
-            "static void pcc_lr_stack__init(pcc_auxil_t auxil, pcc_lr_stack_t *stack) {\n"
+            "static void pcc_lr_stack__init(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_stack_t *stack) {\n"
             "    stack->len = 0;\n"
             "    stack->max = 0;\n"
             "    stack->buf = NULL;\n"
             "}\n"
             "\n"
-            "static void pcc_lr_stack__push(pcc_auxil_t auxil, pcc_lr_stack_t *stack, pcc_lr_entry_t *lr) {\n"
+            "static void pcc_lr_stack__push(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_stack_t *stack, pcc_lr_entry_t *lr) {\n"
             "    if (stack->max <= stack->len) {\n"
             "        const size_t n = stack->len + 1;\n"
             "        size_t m = stack->max;\n"
@@ -4302,11 +4307,11 @@ static bool_t generate(context_t *ctx) {
             "    stack->buf[stack->len++] = lr;\n"
             "}\n"
             "\n"
-            "static pcc_lr_entry_t *pcc_lr_stack__pop(pcc_auxil_t auxil, pcc_lr_stack_t *stack) {\n"
+            "static pcc_lr_entry_t *pcc_lr_stack__pop(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_stack_t *stack) {\n"
             "    return stack->buf[--stack->len];\n"
             "}\n"
             "\n"
-            "static void pcc_lr_stack__term(pcc_auxil_t auxil, pcc_lr_stack_t *stack) {\n"
+            "static void pcc_lr_stack__term(pcc_auxil_t auxil MARK_VAR_AS_USED, pcc_lr_stack_t *stack) {\n"
             "    PCC_FREE(auxil, stack->buf);\n"
             "}\n"
             "\n"
@@ -4589,7 +4594,7 @@ static bool_t generate(context_t *ctx) {
                     }
                     stream__printf(
                         &sstream,
-                        "static void pcc_action_%s_" FMT_LU "(%s_context_t *__pcc_ctx, pcc_thunk_t *__pcc_in, pcc_value_t *__pcc_out) {\n",
+                        "static void pcc_action_%s_" FMT_LU "(%s_context_t *__pcc_ctx MARK_VAR_AS_USED, pcc_thunk_t *__pcc_in MARK_VAR_AS_USED, pcc_value_t *__pcc_out MARK_VAR_AS_USED) {\n",
                         r->name, (ulong_t)d, get_prefix(ctx)
                     );
                     stream__puts(