diff --git a/.idea/rustic-sysy.iml b/.idea/rustic-sysy.iml
index cf84ae4..bbe0a70 100644
--- a/.idea/rustic-sysy.iml
+++ b/.idea/rustic-sysy.iml
@@ -3,6 +3,7 @@
   <component name="NewModuleRootManager">
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/tests" isTestSource="true" />
       <excludeFolder url="file://$MODULE_DIR$/target" />
     </content>
     <orderEntry type="inheritedJdk" />
diff --git a/src/lib.rs b/src/lib.rs
index a33fb60..5768976 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1 @@
-mod tokenizer;
\ No newline at end of file
+pub mod tokenizer;
\ No newline at end of file
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
new file mode 100644
index 0000000..197b016
--- /dev/null
+++ b/src/tokenizer.rs
@@ -0,0 +1,43 @@
+use nom::IResult;
+use crate::tokenizer::parser::{combine_parser, junk_parser};
+
+mod parser;
+
+#[derive(PartialEq, Debug, Copy, Clone)]
+pub enum LexicalTokenType {
+    Identifier,
+    ConstInteger(u32),
+    ConstFloat(f32),
+    Keyword,
+    Delimiter,
+    Operator,
+}
+
+#[derive(PartialEq, Debug, Copy, Clone)]
+pub struct LexicalToken<'a> {
+    pub token_type: LexicalTokenType,
+    pub literal_value: &'a str,
+}
+
+pub fn lexical_parser(mut input: &str) -> IResult<&str, Vec<LexicalToken>> {
+    let mut array = vec![];
+
+    while !input.is_empty() {
+        if let Ok((i, _)) = junk_parser(input) {
+            input = i;
+            continue;
+        }
+
+        if input.is_empty() {
+            break;
+        }
+
+        let (i, token) = combine_parser(input)?;
+        input = i;
+        array.push(token);
+    }
+
+    Ok((input, array))
+}
+
+
diff --git a/src/tokenizer/parser.rs b/src/tokenizer/parser.rs
new file mode 100644
index 0000000..eb0cbcf
--- /dev/null
+++ b/src/tokenizer/parser.rs
@@ -0,0 +1,375 @@
+use crate::tokenizer::{LexicalToken, LexicalTokenType};
+use nom::branch::alt;
+use nom::bytes::complete::{tag, take_until};
+use nom::character::complete::{alpha1, alphanumeric1, digit0, digit1, hex_digit0, multispace1, oct_digit0, one_of};
+use nom::combinator::{map, not, peek, recognize, value};
+use nom::multi::many0_count;
+use nom::sequence::{pair, tuple};
+use nom::IResult;
+use std::str::FromStr;
+
+fn keyword_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(
+        recognize(tuple((
+            alt((
+                tag("break"),
+                tag("const"),
+                tag("continue"),
+                tag("else"),
+                tag("float"),
+                tag("if"),
+                tag("int"),
+                tag("return"),
+                tag("void"),
+                tag("while")
+            )),
+            not(
+                alt((peek(alphanumeric1), tag("_")))
+            )
+        ))),
+        |x| LexicalToken {
+            token_type: LexicalTokenType::Keyword,
+            literal_value: x,
+        },
+    )(input)
+}
+
+fn delimiter_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(
+        alt((
+            tag(","),
+            tag(";"),
+            tag("("),
+            tag(")"),
+            tag("["),
+            tag("]"),
+            tag("{"),
+            tag("}"),
+        )),
+        |x| LexicalToken {
+            token_type: LexicalTokenType::Delimiter,
+            literal_value: x,
+        },
+    )(input)
+}
+
+fn operator_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(
+        alt((
+            tag(">="),
+            tag("<="),
+            tag("=="),
+            tag("!="),
+            tag("&&"),
+            tag("||"),
+            tag("="),
+            tag("+"),
+            tag("-"),
+            tag("!"),
+            tag("*"),
+            tag("/"),
+            tag("%"),
+            tag(">"),
+            tag("<"),
+        )),
+        |x| LexicalToken {
+            token_type: LexicalTokenType::Operator,
+            literal_value: x,
+        },
+    )(input)
+}
+
+fn identifier_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(recognize(pair(
+        alt((alpha1, tag("_"))),
+        many0_count(alt((alphanumeric1, tag("_")))),
+    )), |s| LexicalToken {
+        token_type: LexicalTokenType::Identifier,
+        literal_value: s,
+    })(input)
+}
+
+fn decimal_integer_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(recognize(pair(
+        one_of("123456789"),
+        digit0,
+    )), |x| {
+        let number = u32::from_str_radix(x, 10).unwrap();
+
+        LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(number),
+            literal_value: x,
+        }
+    })(input)
+}
+
+fn octal_integer_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(recognize(pair(
+        tag("0"),
+        oct_digit0,
+    )), |x| {
+        let number = u32::from_str_radix(x, 8).unwrap();
+
+        LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(number),
+            literal_value: x,
+        }
+    })(input)
+}
+
+fn hexadecimal_integer_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(recognize(pair(
+        alt((tag("0x"), tag("0X"))),
+        hex_digit0,
+    )), |x: &str| {
+        let number = u32::from_str_radix(&x[2..], 16).unwrap();
+
+        LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(number),
+            literal_value: x,
+        }
+    })(input)
+}
+
+fn integer_parser(input: &str) -> IResult<&str, LexicalToken> {
+    alt((
+        hexadecimal_integer_parser,
+        octal_integer_parser,
+        decimal_integer_parser,
+    ))(input)
+}
+
+fn float_parser(input: &str) -> IResult<&str, LexicalToken> {
+    map(recognize(tuple((
+        alt((recognize(pair(one_of("123456789"), digit0)), tag("0"))),
+        tag("."),
+        digit1
+    ))), |x| {
+        let number = f32::from_str(x).unwrap();
+
+        LexicalToken {
+            token_type: LexicalTokenType::ConstFloat(number),
+            literal_value: x,
+        }
+    })(input)
+}
+
+fn comments_parser(input: &str) -> IResult<&str, ()> {
+    alt((
+        value((), tuple((
+            tag("//"),
+            take_until("\n"),
+            tag("\n")
+        ))),
+        value((), tuple((
+            tag("/*"),
+            take_until("*/"),
+            tag("*/")
+        )
+        ))
+    ))(input)
+}
+
+pub fn junk_parser(input: &str) -> IResult<&str, ()> {
+    alt((
+        value((), multispace1),
+        comments_parser
+    ))(input)
+}
+
+pub fn combine_parser(input: &str) -> IResult<&str, LexicalToken> {
+    alt((
+        float_parser,
+        integer_parser,
+        keyword_parser,
+        identifier_parser,
+        delimiter_parser,
+        operator_parser,
+    ))(input)
+}
+
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    
+    fn assert_parse(except: LexicalToken, actual: IResult<&str, LexicalToken>) {
+        let (_, token) = actual.unwrap();
+
+        assert_eq!(except, token);
+    }
+
+    #[test]
+    fn keyword_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Keyword,
+            literal_value: "const",
+        }, keyword_parser("const int a = 3;"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Keyword,
+            literal_value: "return",
+        }, keyword_parser("return 0;"));
+    }
+
+    #[test]
+    fn delimiter_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Delimiter,
+            literal_value: "{",
+        }, delimiter_parser("{ int i = 3;}"));
+    }
+
+    #[test]
+    fn operator_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Operator,
+            literal_value: "!=",
+        }, operator_parser("!="));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Operator,
+            literal_value: "!",
+        }, operator_parser("!"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Operator,
+            literal_value: ">=",
+        }, operator_parser(">="));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Operator,
+            literal_value: ">",
+        }, operator_parser("> 123"));
+    }
+
+    #[test]
+    fn identifier_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Identifier,
+            literal_value: "a",
+        }, identifier_parser("a = 3"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Identifier,
+            literal_value: "_123",
+        }, identifier_parser("_123 = NULL"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Identifier,
+            literal_value: "test_123",
+        }, identifier_parser("test_123 += 3"));
+    }
+
+    #[test]
+    fn decimal_integer_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(100),
+            literal_value: "100",
+        }, decimal_integer_parser("100"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(56),
+            literal_value: "56",
+        }, decimal_integer_parser("56 + 44"));
+    }
+
+    #[test]
+    fn octal_integer_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(63),
+            literal_value: "077",
+        }, octal_integer_parser("077"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(0),
+            literal_value: "0",
+        }, octal_integer_parser("0"));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(0),
+            literal_value: "00",
+        }, octal_integer_parser("00"));
+    }
+
+    #[test]
+    fn hexadecimal_integer_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(0),
+            literal_value: "0x0",
+        }, hexadecimal_integer_parser("0x0"));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(0),
+            literal_value: "0X00",
+        }, hexadecimal_integer_parser("0X00"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(15),
+            literal_value: "0xF",
+        }, hexadecimal_integer_parser("0xF"));
+    }
+
+    #[test]
+    fn integer_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(0),
+            literal_value: "0",
+        }, integer_parser("0"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(45),
+            literal_value: "0055",
+        }, integer_parser("0055"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(291),
+            literal_value: "0X123",
+        }, integer_parser("0X123"));
+    }
+
+    #[test]
+    fn float_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstFloat(100.0),
+            literal_value: "100.0",
+        }, float_parser("100.0"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstFloat(0.5),
+            literal_value: "0.5",
+        }, float_parser("0.5"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstFloat(123.456),
+            literal_value: "123.456",
+        }, float_parser("123.456"));
+    }
+
+    #[test]
+    fn combine_parser_test() {
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstInteger(120),
+            literal_value: "120",
+        }, combine_parser("120"));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::ConstFloat(120.11),
+            literal_value: "120.110",
+        }, combine_parser("120.110"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Keyword,
+            literal_value: "const",
+        }, combine_parser("const"));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Identifier,
+            literal_value: "const_number",
+        }, combine_parser("const_number"));
+
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Keyword,
+            literal_value: "int"
+        }, combine_parser("int"));
+        assert_parse(LexicalToken {
+            token_type: LexicalTokenType::Identifier,
+            literal_value: "int_a"
+        }, combine_parser("int_a"));
+    }
+}
\ No newline at end of file
diff --git a/tests/lexical_tests.rs b/tests/lexical_tests.rs
new file mode 100644
index 0000000..2e3add0
--- /dev/null
+++ b/tests/lexical_tests.rs
@@ -0,0 +1,171 @@
+use rustic_sysy::tokenizer::{lexical_parser, LexicalTokenType};
+use rustic_sysy::tokenizer::LexicalTokenType::{ConstInteger, Delimiter, Identifier, Keyword, Operator};
+
+fn validate_tokens(input: &'static str, tokens: Vec<LexicalTokenType>) {
+    let (_, actual_tokens) = lexical_parser(input).unwrap();
+
+    assert_eq!(tokens.len(), actual_tokens.len());
+
+    for (actual, except) in actual_tokens.iter().zip(tokens.iter()) {
+        assert_eq!(&actual.token_type, except,
+                   "The literal value of actual token is {}", actual.literal_value);
+    }
+}
+
+#[test]
+fn main_test() {
+    validate_tokens("int main { return 0; }", vec![
+        Keyword,
+        Identifier,
+        Delimiter,
+        Keyword,
+        ConstInteger(0),
+        Delimiter,
+        Delimiter
+    ]);
+}
+
+#[test]
+fn hexadecimal_test() {
+    validate_tokens("// test hexadecimal define
+int main(){
+    int a;
+    a = 0xf;
+    return a;
+}", vec![
+        Keyword,
+        Identifier,
+        Delimiter,
+        Delimiter,
+        Delimiter,
+        Keyword,
+        Identifier,
+        Delimiter,
+        Identifier,
+        Operator,
+        ConstInteger(15),
+        Delimiter,
+        Keyword,
+        Identifier,
+        Delimiter,
+        Delimiter
+    ]);
+}
+
+#[test]
+fn while_and_if_test() {
+    validate_tokens("
+    // test while-if
+    int whileIf() {
+        int a;
+        a = 0;
+        int b;
+        b = 0;
+        while (a < 100) {
+            if (a == 5) {
+                b = 25;
+            }
+            else if (a == 10) {
+                b = 42;
+            }
+            else {
+                b = a * 2;
+            }
+            a = a + 1;
+        }
+        return (b);
+    }", vec![
+        // int whileIf() {
+        Keyword,
+        Identifier,
+        Delimiter,
+        Delimiter,
+        Delimiter,
+        // int a;
+        Keyword,
+        Identifier,
+        Delimiter,
+        // a = 0;
+        Identifier,
+        Operator,
+        ConstInteger(0),
+        Delimiter,
+        // int b;
+        Keyword,
+        Identifier,
+        Delimiter,
+        // b = 0;
+        Identifier,
+        Operator,
+        ConstInteger(0),
+        Delimiter,
+        // while (a < 100) {
+        Keyword,
+        Delimiter,
+        Identifier,
+        Operator,
+        ConstInteger(100),
+        Delimiter,
+        Delimiter,
+        // if (a == 5) {
+        Keyword,
+        Delimiter,
+        Identifier,
+        Operator,
+        ConstInteger(5),
+        Delimiter,
+        Delimiter,
+        // b = 25;
+        Identifier,
+        Operator,
+        ConstInteger(25),
+        Delimiter,
+        // }
+        Delimiter,
+        // else if (a == 10) {
+        Keyword,
+        Keyword,
+        Delimiter,
+        Identifier,
+        Operator,
+        ConstInteger(10),
+        Delimiter,
+        Delimiter,
+        // b = 42;
+        Identifier,
+        Operator,
+        ConstInteger(42),
+        Delimiter,
+        // }
+        Delimiter,
+        // else {
+        Keyword,
+        Delimiter,
+        // b = a * 2;
+        Identifier,
+        Operator,
+        Identifier,
+        Operator,
+        ConstInteger(2),
+        Delimiter,
+        // }
+        Delimiter,
+        // a = a + 1;
+        Identifier,
+        Operator,
+        Identifier,
+        Operator,
+        ConstInteger(1),
+        Delimiter,
+        // }
+        Delimiter,
+        // return (b);
+        Keyword,
+        Delimiter,
+        Identifier,
+        Delimiter,
+        Delimiter,
+        // }
+        Delimiter
+    ]);
+}