diff --git a/src/nasal_lexer.cpp b/src/nasal_lexer.cpp
index 7ff1f21..425b700 100644
--- a/src/nasal_lexer.cpp
+++ b/src/nasal_lexer.cpp
@@ -35,12 +35,16 @@ bool lexer::is_str(char c) {
     return c=='\'' || c=='\"' || c=='`';
 }
 
+bool lexer::is_quesmark(char c) {
+    return c=='?';
+}
+
 bool lexer::is_single_opr(char c) {
     return (
         c=='(' || c==')' || c=='[' || c==']' ||
         c=='{' || c=='}' || c==',' || c==';' ||
-        c==':' || c=='?' || c=='`' || c=='@' ||
-        c=='%' || c=='$' || c=='\\'
+        c==':' || c=='`' || c=='@' || c=='%' ||
+        c=='$' || c=='\\'
     );
 }
 
@@ -103,6 +107,8 @@ void lexer::open(const std::string& file) {
 }
 
 tok lexer::get_type(const std::string& str) {
+    // search token type from mapper
+    // if cannot find, just return null
     return token_mapper.count(str)? token_mapper.at(str):tok::tk_null;
 }
 
@@ -333,6 +339,24 @@ token lexer::str_gen() {
     };
 }
 
+token lexer::quesmark_gen() {
+    u64 begin_line = line;
+    u64 begin_column = column;
+    std::string str(1, res[ptr]);
+    ++column;
+    ++ptr;
+    if (ptr < res.size() && (res[ptr]=='?' || res[ptr]=='.')) {
+        str += res[ptr];
+        ++column;
+        ++ptr;
+    }
+    return {
+        {begin_line, begin_column, line, column, filename},
+        get_type(str),
+        str
+    };
+}
+
 token lexer::single_opr() {
     u64 begin_line = line;
     u64 begin_column = column;
@@ -398,6 +422,8 @@ const error& lexer::scan(const std::string& file) {
             toks.push_back(num_gen());
         } else if (is_str(res[ptr])) {
             toks.push_back(str_gen());
+        } else if (is_quesmark(res[ptr])) {
+            toks.push_back(quesmark_gen());
         } else if (is_single_opr(res[ptr])) {
             toks.push_back(single_opr());
         } else if (res[ptr]=='.') {
diff --git a/src/nasal_lexer.h b/src/nasal_lexer.h
index 3a00f2b..2e60d65 100644
--- a/src/nasal_lexer.h
+++ b/src/nasal_lexer.h
@@ -50,6 +50,8 @@ enum class tok {
     tk_dot,      // .
     tk_ellipsis, // ...
     tk_quesmark, // ?
+    tk_quesques, // ??
+    tk_quesdot,  // ?.
     tk_colon,    // :
     tk_add,      // operator +
     tk_sub,      // operator -
@@ -79,9 +81,10 @@ enum class tok {
 };
 
 struct token {
-    span loc; // location
-    tok type; // token type
+    span loc;        // location
+    tok type;        // token type
     std::string str; // content
+
     token() = default;
     token(const token&) = default;
 };
@@ -128,6 +131,8 @@ private:
         {"."       , tok::tk_dot     },
         {"..."     , tok::tk_ellipsis},
         {"?"       , tok::tk_quesmark},
+        {"??"      , tok::tk_quesques},
+        {"?."      , tok::tk_quesdot },
         {":"       , tok::tk_colon   },
         {"+"       , tok::tk_add     },
         {"-"       , tok::tk_sub     },
@@ -162,6 +167,7 @@ private:
     bool is_oct(char);
     bool is_dec(char);
     bool is_str(char);
+    bool is_quesmark(char);
     bool is_single_opr(char);
     bool is_calc_opr(char);
 
@@ -173,6 +179,7 @@ private:
     token id_gen();
     token num_gen();
     token str_gen();
+    token quesmark_gen();
     token single_opr();
     token dots();
     token calc_opr();
diff --git a/src/nasal_parse.h b/src/nasal_parse.h
index 3cb334f..5e28d35 100644
--- a/src/nasal_parse.h
+++ b/src/nasal_parse.h
@@ -53,6 +53,8 @@ private:
         {tok::tk_dot     , "."       },
         {tok::tk_ellipsis, "..."     },
         {tok::tk_quesmark, "?"       },
+        {tok::tk_quesques, "??"      },
+        {tok::tk_quesdot , "?."      },
         {tok::tk_colon   , ":"       },
         {tok::tk_add     , "+"       },
         {tok::tk_sub     , "-"       },