diff --git a/src/lib.rs b/src/lib.rs
index dbfe7f3..f045c01 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+pub mod parser;
+
 const VERSION: &str = "0.0.1";
 
 pub fn version() -> &'static str {
diff --git a/src/parser/ast_node/ast_node.rs b/src/parser/ast_node/ast_node.rs
new file mode 100644
index 0000000..644a198
--- /dev/null
+++ b/src/parser/ast_node/ast_node.rs
@@ -0,0 +1,135 @@
+// #[derive(Debug)]
+use super::ast_node_concat::AstNodeConcat;
+use super::ast_node_group::AstNodeGroup;
+use super::ast_node_literal::AstNodeLiteral;
+use super::ast_node_optional::AstNodeOptional;
+use super::ast_node_plus::AstNodePlus;
+use super::ast_node_star::AstNodeStar;
+use super::ast_node_union::AstNodeUnion;
+
+pub(crate) enum AstNode {
+    Literal(AstNodeLiteral),
+    Concat(AstNodeConcat),
+    Union(AstNodeUnion),
+    Star(AstNodeStar),
+    Plus(AstNodePlus),
+    Optional(AstNodeOptional),
+    Group(AstNodeGroup),
+}
+
+impl PartialEq for AstNode {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (AstNode::Literal(lhs), AstNode::Literal(rhs)) => lhs == rhs,
+            (AstNode::Concat(lhs), AstNode::Concat(rhs)) => lhs == rhs,
+            (AstNode::Union(lhs), AstNode::Union(rhs)) => lhs == rhs,
+            (AstNode::Star(lhs), AstNode::Star(rhs)) => lhs == rhs,
+            (AstNode::Plus(lhs), AstNode::Plus(rhs)) => lhs == rhs,
+            (AstNode::Optional(lhs), AstNode::Optional(rhs)) => lhs == rhs,
+            (AstNode::Group(lhs), AstNode::Group(rhs)) => lhs == rhs,
+            _ => false,
+        }
+    }
+}
+
+impl std::fmt::Debug for AstNode {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            AstNode::Literal(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Concat(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Union(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Star(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Plus(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Optional(ast_node) => write!(f, "{:?}", ast_node),
+            AstNode::Group(ast_node) => write!(f, "{:?}", ast_node),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn ast_node_literal_equality() {
+        let node1 = AstNode::Literal(AstNodeLiteral::new('a'));
+        let node2 = AstNode::Literal(AstNodeLiteral::new('a'));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_concat_equality() {
+        let node1 = AstNode::Concat(AstNodeConcat::new(
+            AstNode::Literal(AstNodeLiteral::new('a')),
+            AstNode::Literal(AstNodeLiteral::new('b')),
+        ));
+        let node2 = AstNode::Concat(AstNodeConcat::new(
+            AstNode::Literal(AstNodeLiteral::new('a')),
+            AstNode::Literal(AstNodeLiteral::new('b')),
+        ));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_union_equality() {
+        let node1 = AstNode::Union(AstNodeUnion::new(
+            AstNode::Literal(AstNodeLiteral::new('a')),
+            AstNode::Literal(AstNodeLiteral::new('b')),
+        ));
+        let node2 = AstNode::Union(AstNodeUnion::new(
+            AstNode::Literal(AstNodeLiteral::new('a')),
+            AstNode::Literal(AstNodeLiteral::new('b')),
+        ));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_star_equality() {
+        let node1 = AstNode::Star(AstNodeStar::new(AstNode::Literal(AstNodeLiteral::new('a'))));
+        let node2 = AstNode::Star(AstNodeStar::new(AstNode::Literal(AstNodeLiteral::new('a'))));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_plus_equality() {
+        let node1 = AstNode::Plus(AstNodePlus::new(AstNode::Literal(AstNodeLiteral::new('a'))));
+        let node2 = AstNode::Plus(AstNodePlus::new(AstNode::Literal(AstNodeLiteral::new('a'))));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_optional_equality() {
+        let node1 = AstNode::Optional(AstNodeOptional::new(AstNode::Literal(AstNodeLiteral::new(
+            'a',
+        ))));
+        let node2 = AstNode::Optional(AstNodeOptional::new(AstNode::Literal(AstNodeLiteral::new(
+            'a',
+        ))));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_group_equality() {
+        let node1 = AstNode::Group(AstNodeGroup::new(AstNode::Literal(AstNodeLiteral::new(
+            'a',
+        ))));
+        let node2 = AstNode::Group(AstNodeGroup::new(AstNode::Literal(AstNodeLiteral::new(
+            'a',
+        ))));
+        assert_eq!(node1, node2);
+    }
+
+    #[test]
+    fn ast_node_basic_debug() {
+        let node = AstNode::Concat(AstNodeConcat::new(
+            AstNode::Star(AstNodeStar::new(AstNode::Union(AstNodeUnion::new(
+                AstNode::Literal(AstNodeLiteral::new('a')),
+                AstNode::Literal(AstNodeLiteral::new('b')),
+            )))),
+            AstNode::Optional(AstNodeOptional::new(AstNode::Group(AstNodeGroup::new(
+                AstNode::Plus(AstNodePlus::new(AstNode::Literal(AstNodeLiteral::new('c')))),
+            )))),
+        ));
+        assert_eq!(format!("{:?}", node), "Concat( Star( Union( Literal('a') Literal('b') ) ) Optional( Group( Plus ( Literal('c') ) ) ) )");
+    }
+}
diff --git a/src/parser/ast_node/ast_node_concat.rs b/src/parser/ast_node/ast_node_concat.rs
new file mode 100644
index 0000000..748bacf
--- /dev/null
+++ b/src/parser/ast_node/ast_node_concat.rs
@@ -0,0 +1,27 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodeConcat {
+    m_op1: Box<AstNode>,
+    m_op2: Box<AstNode>,
+}
+
+impl AstNodeConcat {
+    pub(crate) fn new(p0: AstNode, p1: AstNode) -> AstNodeConcat {
+        AstNodeConcat {
+            m_op1: Box::new(p0),
+            m_op2: Box::new(p1),
+        }
+    }
+}
+
+impl PartialEq for AstNodeConcat {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1 && self.m_op2 == other.m_op2
+    }
+}
+
+impl std::fmt::Debug for AstNodeConcat {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Concat( {:?} {:?} )", self.m_op1, self.m_op2)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_group.rs b/src/parser/ast_node/ast_node_group.rs
new file mode 100644
index 0000000..2d390be
--- /dev/null
+++ b/src/parser/ast_node/ast_node_group.rs
@@ -0,0 +1,25 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodeGroup {
+    m_op1: Box<AstNode>,
+}
+
+impl AstNodeGroup {
+    pub(crate) fn new(p0: AstNode) -> AstNodeGroup {
+        AstNodeGroup {
+            m_op1: Box::new(p0),
+        }
+    }
+}
+
+impl PartialEq for AstNodeGroup {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1
+    }
+}
+
+impl std::fmt::Debug for AstNodeGroup {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Group( {:?} )", self.m_op1)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_literal.rs b/src/parser/ast_node/ast_node_literal.rs
new file mode 100644
index 0000000..c23362c
--- /dev/null
+++ b/src/parser/ast_node/ast_node_literal.rs
@@ -0,0 +1,23 @@
+use std::fmt;
+
+pub(crate) struct AstNodeLiteral {
+    m_value: char,
+}
+
+impl AstNodeLiteral {
+    pub(crate) fn new(p0: char) -> AstNodeLiteral {
+        AstNodeLiteral { m_value: p0 }
+    }
+}
+
+impl PartialEq for AstNodeLiteral {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_value == other.m_value
+    }
+}
+
+impl fmt::Debug for AstNodeLiteral {
+    fn fmt(&self, p: &mut fmt::Formatter) -> fmt::Result {
+        write!(p, "Literal({:?})", self.m_value)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_optional.rs b/src/parser/ast_node/ast_node_optional.rs
new file mode 100644
index 0000000..b151262
--- /dev/null
+++ b/src/parser/ast_node/ast_node_optional.rs
@@ -0,0 +1,25 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodeOptional {
+    m_op1: Box<AstNode>,
+}
+
+impl AstNodeOptional {
+    pub(crate) fn new(p0: AstNode) -> AstNodeOptional {
+        AstNodeOptional {
+            m_op1: Box::new(p0),
+        }
+    }
+}
+
+impl PartialEq for AstNodeOptional {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1
+    }
+}
+
+impl std::fmt::Debug for AstNodeOptional {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Optional( {:?} )", self.m_op1)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_plus.rs b/src/parser/ast_node/ast_node_plus.rs
new file mode 100644
index 0000000..ea1e006
--- /dev/null
+++ b/src/parser/ast_node/ast_node_plus.rs
@@ -0,0 +1,25 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodePlus {
+    m_op1: Box<AstNode>,
+}
+
+impl AstNodePlus {
+    pub(crate) fn new(p0: AstNode) -> AstNodePlus {
+        AstNodePlus {
+            m_op1: Box::new(p0),
+        }
+    }
+}
+
+impl PartialEq for AstNodePlus {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1
+    }
+}
+
+impl std::fmt::Debug for AstNodePlus {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Plus ( {:?} )", self.m_op1)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_star.rs b/src/parser/ast_node/ast_node_star.rs
new file mode 100644
index 0000000..8ca1c63
--- /dev/null
+++ b/src/parser/ast_node/ast_node_star.rs
@@ -0,0 +1,25 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodeStar {
+    m_op1: Box<AstNode>,
+}
+
+impl AstNodeStar {
+    pub(crate) fn new(p0: AstNode) -> AstNodeStar {
+        AstNodeStar {
+            m_op1: Box::new(p0),
+        }
+    }
+}
+
+impl PartialEq for AstNodeStar {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1
+    }
+}
+
+impl std::fmt::Debug for AstNodeStar {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Star( {:?} )", self.m_op1)
+    }
+}
diff --git a/src/parser/ast_node/ast_node_union.rs b/src/parser/ast_node/ast_node_union.rs
new file mode 100644
index 0000000..5cfe82a
--- /dev/null
+++ b/src/parser/ast_node/ast_node_union.rs
@@ -0,0 +1,27 @@
+use crate::parser::ast_node::ast_node::AstNode;
+
+pub(crate) struct AstNodeUnion {
+    m_op1: Box<AstNode>,
+    m_op2: Box<AstNode>,
+}
+
+impl AstNodeUnion {
+    pub(crate) fn new(p0: AstNode, p1: AstNode) -> AstNodeUnion {
+        AstNodeUnion {
+            m_op1: Box::new(p0),
+            m_op2: Box::new(p1),
+        }
+    }
+}
+
+impl PartialEq for AstNodeUnion {
+    fn eq(&self, other: &Self) -> bool {
+        self.m_op1 == other.m_op1 && self.m_op2 == other.m_op2
+    }
+}
+
+impl std::fmt::Debug for AstNodeUnion {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "Union( {:?} {:?} )", self.m_op1, self.m_op2)
+    }
+}
diff --git a/src/parser/ast_node/mod.rs b/src/parser/ast_node/mod.rs
new file mode 100644
index 0000000..35a6ec4
--- /dev/null
+++ b/src/parser/ast_node/mod.rs
@@ -0,0 +1,8 @@
+pub mod ast_node;
+mod ast_node_concat;
+mod ast_node_group;
+mod ast_node_literal;
+mod ast_node_optional;
+mod ast_node_plus;
+mod ast_node_star;
+mod ast_node_union;
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
new file mode 100644
index 0000000..b8b7e88
--- /dev/null
+++ b/src/parser/mod.rs
@@ -0,0 +1,2 @@
+// Keep ASTNode private and they will be used by parser in the future
+mod ast_node;