diff --git a/src/nasal.h b/src/nasal.h
index 0c59625..225ee82 100644
--- a/src/nasal.h
+++ b/src/nasal.h
@@ -38,7 +38,7 @@ const char* get_platform();
 const char* get_arch();
 
 // virtual machine stack depth, both global depth and value stack depth
-const u32 STACK_DEPTH = 4096;
+const u32 VM_STACK_DEPTH = UINT16_MAX;
 
 f64 hex_to_f64(const char*);
 f64 oct_to_f64(const char*);
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index 86fb620..ab5e42e 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -309,7 +309,7 @@ void codegen::func_gen(function* node) {
     // the local scope should not cause stack overflow
     // and should not greater than upvalue's max size(65536)
     code[lsize].num = local.back().size();
-    if (local.back().size()>=STACK_DEPTH || local.back().size()>=UINT16_MAX) {
+    if (local.back().size()>=VM_STACK_DEPTH || local.back().size()>=UINT16_MAX) {
         die("too many local variants: " +
             std::to_string(local.back().size()),
             block->get_location()
@@ -1361,7 +1361,7 @@ const error& codegen::compile(parse& parse,
     }
 
     // check global variables size
-    if (global.size()>=STACK_DEPTH/2) {
+    if (global.size()>=VM_STACK_DEPTH) {
         err.err("code",
             "too many global variables: " +
             std::to_string(global.size())
diff --git a/src/nasal_codegen.h b/src/nasal_codegen.h
index e171f83..2b4ba53 100644
--- a/src/nasal_codegen.h
+++ b/src/nasal_codegen.h
@@ -87,7 +87,7 @@ private:
     std::list<std::vector<u64>> break_ptr;
 
     // symbol table
-    // global : max STACK_DEPTH-1 values
+    // global : max VM_STACK_DEPTH-1 values
     std::unordered_map<std::string, u64> global;
 
     // nasal namespace
@@ -95,7 +95,7 @@ private:
     std::unordered_map<std::string, std::unordered_set<std::string>> nasal_namespace;
 
     // local  : max 32768 upvalues 65536 values
-    // but in fact local scope also has less than STACK_DEPTH value
+    // but in fact local scope also has less than VM_STACK_DEPTH value
     std::list<std::unordered_map<std::string, u64>> local;
 
     void check_id_exist(identifier*);
diff --git a/src/nasal_lexer.h b/src/nasal_lexer.h
index a37ebe4..461b03d 100644
--- a/src/nasal_lexer.h
+++ b/src/nasal_lexer.h
@@ -36,7 +36,7 @@ enum class tok:u32 {
     rif,      // condition expression keyword if
     elsif,    // condition expression keyword elsif
     relse,    // condition expression keyword else
-    tknil,    // nil literal
+    nil,      // nil literal
     lcurve,   // (
     rcurve,   // )
     lbracket, // [
@@ -114,7 +114,7 @@ private:
         {"if"      ,tok::rif     },
         {"elsif"   ,tok::elsif   },
         {"else"    ,tok::relse   },
-        {"nil"     ,tok::tknil   },
+        {"nil"     ,tok::nil     },
         {"("       ,tok::lcurve  },
         {")"       ,tok::rcurve  },
         {"["       ,tok::lbracket},
diff --git a/src/nasal_parse.cpp b/src/nasal_parse.cpp
index 8bc0159..163c9bb 100644
--- a/src/nasal_parse.cpp
+++ b/src/nasal_parse.cpp
@@ -256,7 +256,7 @@ vector_expr* parse::vec() {
     // array end with tok::null=0
     const tok panic[] = {
         tok::id, tok::str, tok::num, tok::tktrue,
-        tok::tkfalse, tok::opnot, tok::sub, tok::tknil,
+        tok::tkfalse, tok::opnot, tok::sub, tok::nil,
         tok::func, tok::var, tok::lcurve, tok::floater,
         tok::lbrace, tok::lbracket, tok::null
     };
@@ -372,7 +372,7 @@ expr* parse::expression() {
     }
     switch(type) {
         case tok::use: return use_stmt_gen();
-        case tok::tknil:
+        case tok::nil:
         case tok::num:
         case tok::str:
         case tok::id:
@@ -637,9 +637,9 @@ unary_operator* parse::unary() {
 
 expr* parse::scalar() {
     expr* node = nullptr;
-    if (lookahead(tok::tknil)) {
+    if (lookahead(tok::nil)) {
         node = nil();
-        match(tok::tknil);
+        match(tok::nil);
     } else if (lookahead(tok::num)) {
         node = num();
     } else if (lookahead(tok::str)) {
@@ -715,7 +715,7 @@ call_vector* parse::callv() {
     // array end with tok::null=0
     const tok panic[] = {
         tok::id, tok::str, tok::num, tok::tktrue,
-        tok::tkfalse, tok::opnot, tok::sub, tok::tknil,
+        tok::tkfalse, tok::opnot, tok::sub, tok::nil,
         tok::func, tok::var, tok::lcurve, tok::floater,
         tok::lbrace, tok::lbracket, tok::colon, tok::null
     };
@@ -745,7 +745,7 @@ call_function* parse::callf() {
     // array end with tok::null=0
     const tok panic[] = {
         tok::id, tok::str, tok::num, tok::tktrue,
-        tok::tkfalse, tok::opnot, tok::sub, tok::tknil,
+        tok::tkfalse, tok::opnot, tok::sub, tok::nil,
         tok::func, tok::var, tok::lcurve, tok::floater,
         tok::lbrace, tok::lbracket, tok::null
     };
@@ -844,7 +844,7 @@ tuple_expr* parse::multi_scalar() {
     // we will check if value called here can reach a memory space
     const tok panic[] = {
         tok::id, tok::str, tok::num, tok::tktrue,
-        tok::tkfalse, tok::opnot, tok::sub, tok::tknil,
+        tok::tkfalse, tok::opnot, tok::sub, tok::nil,
         tok::func, tok::var, tok::lcurve, tok::floater,
         tok::lbrace, tok::lbracket, tok::null
     };
@@ -1070,7 +1070,7 @@ return_expr* parse::return_expression() {
     auto node = new return_expr(toks[ptr].loc);
     match(tok::ret);
     tok type = toks[ptr].type;
-    if (type==tok::tknil || type==tok::num ||
+    if (type==tok::nil || type==tok::num ||
         type==tok::str || type==tok::id ||
         type==tok::func || type==tok::sub ||
         type==tok::opnot || type==tok::lcurve ||
diff --git a/src/nasal_parse.h b/src/nasal_parse.h
index 2d8ff27..85d351c 100644
--- a/src/nasal_parse.h
+++ b/src/nasal_parse.h
@@ -37,7 +37,7 @@ private:
         {tok::rif     ,"if"      },
         {tok::elsif   ,"elsif"   },
         {tok::relse   ,"else"    },
-        {tok::tknil   ,"nil"     },
+        {tok::nil     ,"nil"     },
         {tok::lcurve  ,"("       },
         {tok::rcurve  ,")"       },
         {tok::lbracket,"["       },
diff --git a/src/nasal_type.cpp b/src/nasal_type.cpp
index 693bc15..91feb10 100644
--- a/src/nasal_type.cpp
+++ b/src/nasal_type.cpp
@@ -171,14 +171,14 @@ void nas_co::clear() {
     if (!ctx.stack) {
         return;
     }
-    for(u32 i = 0; i<STACK_DEPTH; ++i) {
+    for(u32 i = 0; i<VM_STACK_DEPTH; ++i) {
         ctx.stack[i] = var::nil();
     }
 
     ctx.pc = 0;
     ctx.localr = nullptr;
     ctx.memr = nullptr;
-    ctx.canary = ctx.stack+STACK_DEPTH-1;
+    ctx.canary = ctx.stack+VM_STACK_DEPTH-1;
     ctx.top = ctx.stack;
     ctx.funcr = var::nil();
     ctx.upvalr = var::nil();
diff --git a/src/nasal_type.h b/src/nasal_type.h
index d7e3b9d..499befc 100644
--- a/src/nasal_type.h
+++ b/src/nasal_type.h
@@ -234,7 +234,7 @@ struct nas_co {
     status status;
 
     nas_co() {
-        ctx.stack = new var[STACK_DEPTH];
+        ctx.stack = new var[VM_STACK_DEPTH];
         clear();
     }
     ~nas_co() {
diff --git a/src/nasal_vm.cpp b/src/nasal_vm.cpp
index 38edde4..14e80ac 100644
--- a/src/nasal_vm.cpp
+++ b/src/nasal_vm.cpp
@@ -49,14 +49,14 @@ void vm::context_and_global_init() {
     ctx.funcr = nil;
     ctx.upvalr = nil;
 
-    /* set canary = stack[STACK_DEPTH-1] */
-    ctx.canary = ctx.stack+STACK_DEPTH-1;
+    /* set canary = stack[VM_STACK_DEPTH-1] */
+    ctx.canary = ctx.stack+VM_STACK_DEPTH-1;
 
     /* nothing is on stack */
     ctx.top = ctx.stack - 1;
 
     /* clear main stack and global */
-    for(u32 i = 0; i<STACK_DEPTH; ++i) {
+    for(u32 i = 0; i<VM_STACK_DEPTH; ++i) {
         ctx.stack[i] = nil;
         global[i] = nil;
     }
diff --git a/src/nasal_vm.h b/src/nasal_vm.h
index 9e2688c..88920b9 100644
--- a/src/nasal_vm.h
+++ b/src/nasal_vm.h
@@ -176,8 +176,8 @@ public:
 
     /* constructor of vm instance */
     vm() {
-        ctx.stack = new var[STACK_DEPTH];
-        global = new var[STACK_DEPTH];
+        ctx.stack = new var[VM_STACK_DEPTH];
+        global = new var[VM_STACK_DEPTH];
     }
     ~vm() {
         delete[] ctx.stack;