diff --git a/src/lib.rs b/src/lib.rs
index 4a92cb3..3b5a836 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,7 @@
 use std::error::Error;
 use crate::parser::tokenizer::tokenize;
 use crate::parser::sanitizer::sanitize_tokens;
-use crate::parser::ast_builder::build_ast;
+use crate::parser::ast_builder::{build_ast, Node};
 
 pub mod parser;
 
@@ -15,15 +15,15 @@ struct _GaussianRational {
     imaginary: _Rational,
 }
 
-pub fn parse(query: &str) -> Result<Vec<f64>, Box<dyn Error>> {
+pub fn parse(query: &str) -> Result<Node, Box<dyn Error>> {
     let tokens = tokenize(query)?;
     println!("{:?}", tokens);
     let sanitized_tokens = sanitize_tokens(tokens)?;
     println!("{:?}", sanitized_tokens);
-    let _ast = build_ast(sanitized_tokens);
+    let ast = build_ast(sanitized_tokens);
+    println!("{:?}", ast);
 
-
-    Ok(vec![])
+    Ok(ast)
 }
 
 fn print_reduced_form(equation: &Vec<f64>) {
@@ -113,36 +113,4 @@ pub fn solve(equation: Vec<f64>) {
 #[cfg(test)]
 mod tests {
     use super::*;
-
-    #[test]
-    fn parse_degree_0() {
-        let query = "5 * X^0 = 3 * X^0";
-        let result: Vec<f64> = vec![2.];
-
-        assert_eq!(parse(query).unwrap(), result);
-    }
-
-    #[test]
-    fn parse_degree_1() {
-        let query = "5 * X^0 + 3 * X^1 = 3 * X^0";
-        let result: Vec<f64> = vec![2., 3.];
-
-        assert_eq!(parse(query).unwrap(), result);
-    }
-
-    #[test]
-    fn parse_degree_2() {
-        let query = "5 * X^0 + 6 * X^1 + 8 * X^2 = 3 * X^0 - 2 * X^2";
-        let result = vec![2., 6., 10.];
-
-        assert_eq!(parse(query).unwrap(), result);
-    }
-
-    #[test]
-    fn parse_random_order() {
-        let query = "9.3 * X^3 + 4.3 * X^0 + 3.4 * X^2 - 1.5 * X^3 - 13.12 * X^1 = 1.4 * X^2 - 5.1 * X^3 + 1.4 * X^1 -6.3 * X^0";
-        let result = vec![10.6, -14.52, 2., 12.9];
-
-        assert_eq!(parse(query).unwrap(), result);
-    }
 }
diff --git a/src/main.rs b/src/main.rs
index 9776ba8..535d588 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,9 +3,9 @@ use std::process;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
-    let equation = computorv1::parse(&args[1]).unwrap_or_else(|e| {
+    let _equation = computorv1::parse(&args[1]).unwrap_or_else(|e| {
         println!("Error during parsing: {e}");
         process::exit(1);
     });
-    computorv1::solve(equation);
+    //computorv1::solve(equation);
 }
diff --git a/src/parser/ast_builder.rs b/src/parser/ast_builder.rs
index ffd67ec..9bb8038 100644
--- a/src/parser/ast_builder.rs
+++ b/src/parser/ast_builder.rs
@@ -1,10 +1,471 @@
 use super::Token;
 
-pub struct Node {
-    _lhs: Option<Box<Node>>,
-    _rhs: Option<Box<Node>>,
+#[derive(Debug, PartialEq, Clone)]
+pub struct Rational {
+    numerator: i128,
+    denominator: i128,
 }
 
-pub fn build_ast(_tokens: Vec<Token>) -> Node {
-    Node { _lhs: None, _rhs: None }
+#[derive(Debug, PartialEq, Clone)]
+pub struct GaussianRational {
+    real: Rational,
+    imaginary: Rational,
+}
+
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum Node {
+    Leaf(Vec<GaussianRational>),
+    Internal {
+        operator: Token,
+        lhs: Box<Node>,
+        rhs: Box<Node>,
+    }
+}
+
+/*
+   pub struct Node {
+   _lhs: Option<Box<Node>>,
+   _rhs: Option<Box<Node>>,
+   }
+   */
+
+fn zero() -> GaussianRational {
+    GaussianRational {
+        real: Rational {
+            numerator: 0,
+            denominator: 1,
+        },
+        imaginary: Rational {
+            numerator: 0,
+            denominator: 1,
+        }
+    }
+}
+
+fn minus_one() -> GaussianRational {
+    GaussianRational {
+        real: Rational {
+            numerator: -1,
+            denominator: 1,
+        },
+        imaginary: Rational {
+            numerator: 0,
+            denominator: 1,
+        }
+    }
+}
+
+fn one() -> GaussianRational {
+    GaussianRational {
+        real: Rational {
+            numerator: 1,
+            denominator: 1,
+        },
+        imaginary: Rational {
+            numerator: 0,
+            denominator: 1,
+        }
+    }
+}
+
+fn i() -> GaussianRational {
+    GaussianRational {
+        real: Rational {
+            numerator: 0,
+            denominator: 1,
+        },
+        imaginary: Rational {
+            numerator: 1,
+            denominator: 1,
+        }
+    }
+}
+
+fn minus_i() -> GaussianRational {
+    GaussianRational {
+        real: Rational {
+            numerator: 0,
+            denominator: 1,
+        },
+        imaginary: Rational {
+            numerator: -1,
+            denominator: 1,
+        }
+    }
+}
+
+fn x() -> Vec<GaussianRational> {
+    vec![zero(), one()]
+}
+
+fn minus_x() -> Vec<GaussianRational> {
+    vec![zero(), minus_one()]
+}
+
+fn insert_operator_node(mut tokens: Vec<Token>, position: usize) -> Node {
+    let tokens_right = tokens.split_off(position + 1);
+    let token = tokens.pop().unwrap();
+    Node::Internal {
+        operator: token,
+        lhs: Box::new(build_ast(tokens)),
+        rhs: Box::new(build_ast(tokens_right)),
+    }
+}
+
+fn get_parentheses_map(tokens: &Vec<Token>) -> Vec<usize> {
+    let mut parentheses_map = vec![];
+    let mut score = 0;
+    for token in tokens {
+        match token {
+            Token::OpenParenthesis() => score += 1,
+            Token::CloseParenthesis() => score -= 1,
+            _ => (),
+        }
+        parentheses_map.push(score);
+    }
+    parentheses_map
+}
+
+fn parse_number(string: &String, sign: i128) -> GaussianRational {
+    let mut number = Rational {
+        numerator: 0,
+        denominator: 1,
+    };
+    let mut is_floating = false;
+
+    for c in string.chars() {
+        match c {
+            '.' => is_floating = true,
+            '0'..='9' => {
+                number.numerator = 10 * number.numerator + String::from(c).parse::<i128>().unwrap();
+                if is_floating == true {
+                    number.denominator *= 10;
+                }
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    number.numerator *= sign;
+
+    GaussianRational {
+        real: number,
+        imaginary: Rational {
+            numerator: 0,
+            denominator: 1,
+        }
+    }
+}
+
+fn check_parentheses(tokens: &Vec<Token>) -> bool {
+    let mut level = 0;
+    let mut count = 0;
+    for token in tokens {
+        match token {
+            Token::OpenParenthesis() => level += 1,
+            Token::CloseParenthesis() => level -= 1,
+            _ => (),
+        }
+        count += 1;
+        if level == 0 {
+            break;
+        }
+    }
+
+    count == tokens.len()
+}
+
+pub fn build_ast(mut tokens: Vec<Token>) -> Node {
+    //let mut tokens_copy = tokens.clone();
+    //let mut not_done = true;
+
+    // Lowest prio : equal
+    let split = tokens.iter().position(|x| x == &Token::Equal());
+    if let Some(position) = split {
+        return insert_operator_node(tokens, position);
+    }
+
+    while tokens.starts_with(&[Token::OpenParenthesis()]) && tokens.ends_with(&[Token::CloseParenthesis()]) && check_parentheses(&tokens) == true {
+        tokens = tokens.split_off(1);
+        tokens.pop();
+    }
+
+    let parentheses_map = get_parentheses_map(&tokens);
+    //let iter = zip(tokens, parentheses_map);
+    // Lowest prio : rightest minus or plus, also manages minus unary operator
+    let split = tokens.iter().enumerate().rposition(|(i, x)| parentheses_map[i] == 0 && (x == &Token::Addition() || x == &Token::Substraction()));
+    if let Some(position) = split {
+        let tokens_right = tokens.split_off(position + 1);
+        let token = tokens.pop().unwrap();
+        if tokens.len() == 0 {
+            match &tokens_right[0] {
+                Token::Number(n) => return Node::Leaf(vec![parse_number(n, -1)]),
+                Token::ImaginaryUnit() => return Node::Leaf(vec![minus_i()]),
+                Token::Variable(_) => return Node::Leaf(minus_x()),
+                _ => (),
+            }
+        }
+        return Node::Internal {
+            operator: token,
+            lhs: Box::new(build_ast(tokens)),
+            rhs: Box::new(build_ast(tokens_right)),
+        }
+    }
+
+    // Lowest prio : righest times or divide or modulo
+    let split = tokens.iter().enumerate().rposition(|(i, x)| parentheses_map[i] == 0 && (x == &Token::Multiplication() || x == &Token::Division() || x == &Token::Modulo()));
+    if let Some(position) = split {
+        return insert_operator_node(tokens, position);
+    }
+    // Lowest prio : exponentiation
+    let split = tokens.iter().enumerate().rposition(|(i, x)| parentheses_map[i] == 0 && x == &Token::Exponentiation());
+    if let Some(position) = split {
+        return insert_operator_node(tokens, position);
+    }
+
+    match &tokens[0] {
+        Token::Number(n) => return Node::Leaf(vec![parse_number(n, 1)]),
+        Token::ImaginaryUnit() => return Node::Leaf(vec![i()]),
+        Token::Variable(_) => return Node::Leaf(x()),
+        _ => (),
+    }
+    unreachable!();
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn one_token() -> Token {
+        Token::Number(String::from("1"))
+    }
+
+    fn two_token() -> Token {
+        Token::Number(String::from("2"))
+    }
+
+    fn x_token() -> Token {
+        Token::Variable(String::from("x"))
+    }
+
+    fn i_token() -> Token {
+        Token::ImaginaryUnit()
+    }
+
+    fn open() -> Token {
+        Token::OpenParenthesis()
+    }
+
+    fn close() -> Token {
+        Token::CloseParenthesis()
+    }
+
+    fn plus() -> Token {
+        Token::Addition()
+    }
+
+    fn minus() -> Token {
+        Token::Substraction()
+    }
+
+    fn times() -> Token {
+        Token::Multiplication()
+    }
+
+    fn divided_by() -> Token {
+        Token::Division()
+    }
+
+    fn modulo() -> Token {
+        Token::Modulo()
+    }
+
+    fn power() -> Token {
+        Token::Exponentiation()
+    }
+
+    fn equals() -> Token {
+        Token::Equal()
+    }
+
+    #[test]
+    fn one_equals_one() {
+        let tokens = vec![one_token(), equals(), one_token()];
+        let results = Node::Internal {
+            operator: Token::Equal(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+
+    }
+
+    #[test]
+    fn one_plus_one() {
+        let tokens = vec![one_token(), plus(), one_token()];
+        let results = Node::Internal {
+            operator: plus(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![one_token(), minus(), one_token()];
+        let results = Node::Internal {
+            operator: minus(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn one_times_one() {
+        let tokens = vec![one_token(), times(), one_token()];
+        let results = Node::Internal {
+            operator: times(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![one_token(), divided_by(), one_token()];
+        let results = Node::Internal {
+            operator: divided_by(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![one_token(), modulo(), one_token()];
+        let results = Node::Internal {
+            operator: modulo(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn one_power_one() {
+        let tokens = vec![one_token(), power(), one_token()];
+        let results = Node::Internal {
+            operator: power(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn left_priority() {
+        let tokens = vec![one_token(), plus(), one_token(), minus(), one_token()];
+        let results = Node::Internal {
+            operator: minus(),
+            lhs: Box::new(Node::Internal {
+                operator: plus(),
+                lhs: Box::new(Node::Leaf(vec![one()])),
+                rhs: Box::new(Node::Leaf(vec![one()]))
+            }),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn operation_priority() {
+        let tokens = vec![one_token(), plus(), one_token(), times(), one_token()];
+        let results = Node::Internal {
+            operator: plus(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Internal {
+                operator: times(),
+                lhs: Box::new(Node::Leaf(vec![one()])),
+                rhs: Box::new(Node::Leaf(vec![one()]))
+            })
+        };
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn i_plus_i() {
+        let tokens = vec![i_token(), plus(), i_token()];
+        let results = Node::Internal {
+            operator: plus(),
+            lhs: Box::new(Node::Leaf(vec![i()])),
+            rhs: Box::new(Node::Leaf(vec![i()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn x_plus_x() {
+        let tokens = vec![x_token(), plus(), x_token()];
+        let results = Node::Internal {
+            operator: plus(),
+            lhs: Box::new(Node::Leaf(x())),
+            rhs: Box::new(Node::Leaf(x()))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn parentheses() {
+        let tokens = vec![one_token(), times(), open(), one_token(), plus(), one_token(), close()];
+        let results = Node::Internal {
+            operator: times(),
+            lhs: Box::new(Node::Leaf(vec![one()])),
+            rhs: Box::new(Node::Internal {
+                operator: plus(),
+                lhs: Box::new(Node::Leaf(vec![one()])),
+                rhs: Box::new(Node::Leaf(vec![one()]))
+            })
+        };
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn two_plus_two() {
+        let mut two = one();
+        two.real.numerator = 2;
+
+        let tokens = vec![two_token(), plus(), two_token()];
+        let results = Node::Internal {
+            operator: plus(),
+            lhs: Box::new(Node::Leaf(vec![two.clone()])),
+            rhs: Box::new(Node::Leaf(vec![two.clone()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![two_token(), minus(), one_token()];
+        let results = Node::Internal {
+            operator: minus(),
+            lhs: Box::new(Node::Leaf(vec![two])),
+            rhs: Box::new(Node::Leaf(vec![one()]))
+        };
+
+        assert_eq!(build_ast(tokens), results);
+    }
+
+    #[test]
+    fn negative_one() {
+        let tokens = vec![minus(), one_token()];
+        let results = Node::Leaf(vec![minus_one()]);
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![minus(), x_token()];
+        let results = Node::Leaf(minus_x());
+        assert_eq!(build_ast(tokens), results);
+
+        let tokens = vec![minus(), i_token()];
+        let results = Node::Leaf(vec![minus_i()]);
+        assert_eq!(build_ast(tokens), results);
+    }
 }