diff --git a/src/cell.rs b/src/cell.rs
new file mode 100644
index 0000000..5a196dd
--- /dev/null
+++ b/src/cell.rs
@@ -0,0 +1,77 @@
+use std::collections::HashSet;
+
+use crate::evaluator::*;
+
+#[derive(Clone)]
+pub struct Cell {
+    eval: Option<Eval>,
+    raw: String,
+    deps: HashSet<CellRef>,
+}
+
+impl Cell {
+    pub fn new(eval: Option<Eval>, raw: String) -> Self {
+        Self {
+            eval,
+            raw,
+            deps: HashSet::new(),
+        }
+    }
+
+    pub fn raw(&self) -> String {
+        self.raw.clone()
+    }
+
+    pub fn eval(&self) -> Option<Eval> {
+        self.eval.clone()
+    }
+}
+
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub struct CellRef {
+    pub row: i64,
+    pub col: i64,
+}
+
+impl CellRef {
+    pub fn new(s: String) -> Result<CellRef, String> {
+        let s = s.trim();
+        let mut col: i64 = 0;
+        let mut i = 0;
+
+        // consume leading letters for the column
+        for (idx, ch) in s.char_indices() {
+            if ch.is_ascii_alphabetic() {
+                let u = ch.to_ascii_uppercase() as u8;
+                let val = (u - b'A' + 1) as i64; // A->1 ... Z->26
+                col = col * 26 + val;
+                i = idx + ch.len_utf8();
+            } else {
+                break;
+            }
+        }
+
+        if col <= 0 {
+            return Err(format!(
+                "Parse error: missing column letters in cell ref: {s}"
+            ));
+        }
+
+        let row_part = &s[i..];
+        if row_part.is_empty() {
+            return Err(format!(
+                "Parse error: missing column letters in cell ref: {s}"
+            ));
+        } else if !row_part.chars().all(|c| c.is_ascii_digit()) {
+            return Err(format!(
+                "Parse error: row part must be numeric in cell ref: {s}"
+            ));
+        }
+
+        if let Ok(row) = row_part.parse::<i64>() {
+            Ok(CellRef { row, col })
+        } else {
+            Err(format!("Parse error: invalid row number."))
+        }
+    }
+}
diff --git a/src/evaluator.rs b/src/evaluator.rs
index ee5f412..4b9958e 100644
--- a/src/evaluator.rs
+++ b/src/evaluator.rs
@@ -1,8 +1,10 @@
+use crate::cell::{Cell, CellRef};
 use crate::parser::*;
 use crate::tokenizer::Literal;
+use std::collections::HashMap;
 use std::fmt;
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum Eval {
     Literal(Literal),
     Expr(Expr),
@@ -17,25 +19,70 @@ impl fmt::Display for Eval {
     }
 }
 
-pub fn _evaluate(expr: &mut Expr) -> Result<Eval, String> {
-    let res = match expr {
-        Expr::Literal(lit) => Eval::Literal(lit.clone()),
-        Expr::Infix { op, lhs, rhs } => {
-            let lval = _evaluate(lhs)?;
-            let rval = _evaluate(rhs)?;
+pub struct Evaluator {
+    cells: HashMap<CellRef, Cell>,
+}
 
-            match op {
-                InfixOp::ADD => eval_add(&lval, &rval)?,
-                InfixOp::SUB => eval_sub(&lval, &rval)?,
-                InfixOp::MUL => eval_mul(&lval, &rval)?,
-                InfixOp::DIV => eval_div(&lval, &rval)?,
-                _ => return Err(format!("Evaluation error: Unsupported operator {:?}", op)),
-            }
+impl Evaluator {
+    pub fn new() -> Evaluator {
+        return Evaluator {
+            cells: HashMap::new(),
+        };
+    }
+
+    pub fn set_cell(&mut self, cell_ref: CellRef, raw_val: String) -> Result<(), String> {
+        if self.cells.contains_key(&cell_ref) && self.cells[&cell_ref].raw() == raw_val {
+            return Ok(());
         }
-        it => return Err(format!("Evaluation error: Unsupported expression {:?}", it)),
-    };
 
-    Ok(res)
+        let mut eval: Option<Eval> = None;
+        if let Some(c) = raw_val.chars().nth(0)
+            && c == '='
+        {
+            if let Ok(e) = self.evaluate(raw_val[1..].to_owned()) {
+                eval = Some(e);
+            };
+        }
+
+        self.cells.insert(cell_ref, Cell::new(eval, raw_val));
+        Ok(())
+    }
+
+    pub fn get_cell(&mut self, cell_ref: CellRef) -> Result<(String, Option<Eval>), String> {
+        if !self.cells.contains_key(&cell_ref) {
+            return Err(format!("Cell at {:?} not found.", cell_ref));
+        }
+
+        let cell = &self.cells[&cell_ref];
+
+        Ok((cell.raw(), cell.eval()))
+    }
+
+    pub fn evaluate(&self, str: String) -> Result<Eval, String> {
+        let mut expr = parse(&str)?;
+        self.evaluate_expr(&mut expr)
+    }
+
+    fn evaluate_expr(&self, expr: &mut Expr) -> Result<Eval, String> {
+        let res = match expr {
+            Expr::Literal(lit) => Eval::Literal(lit.clone()),
+            Expr::Infix { op, lhs, rhs } => {
+                let lval = self.evaluate_expr(lhs)?;
+                let rval = self.evaluate_expr(rhs)?;
+
+                match op {
+                    InfixOp::ADD => eval_add(&lval, &rval)?,
+                    InfixOp::SUB => eval_sub(&lval, &rval)?,
+                    InfixOp::MUL => eval_mul(&lval, &rval)?,
+                    InfixOp::DIV => eval_div(&lval, &rval)?,
+                    _ => return Err(format!("Evaluation error: Unsupported operator {:?}", op)),
+                }
+            }
+            it => return Err(format!("Evaluation error: Unsupported expression {:?}", it)),
+        };
+
+        Ok(res)
+    }
 }
 
 fn eval_add(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
@@ -59,16 +106,43 @@ fn eval_add(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
 }
 
 fn eval_sub(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
-    Err("Todo.".to_string())
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x - y, |x, y| x - y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for SUB function.".to_string())
+        }
+        _ => return Err("Evalutation error: expected literals for SUB function.".to_string()),
+    }
 }
 fn eval_mul(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
-    Err("Todo.".to_string())
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x * y, |x, y| x * y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for MUL function.".to_string())
+        }
+        _ => return Err("Evalutation error: expected literals for MUL function.".to_string()),
+    }
 }
 fn eval_div(lval: &Eval, rval: &Eval) -> Result<Eval, String> {
-    Err("Todo.".to_string())
+    match (lval, rval) {
+        (Eval::Literal(a), Eval::Literal(b)) => {
+            if let Some(res) = eval_numeric_infix(a, b, |x, y| x / y, |x, y| x / y) {
+                return Ok(Eval::Literal(res));
+            }
+
+            Err("Evaluation error: expected string or numeric types for DIV function.".to_string())
+        }
+        _ => return Err("Evalutation error: expected literals for DIV function.".to_string()),
+    }
 }
 
-pub fn eval_numeric_infix<FInt, FDouble>(
+fn eval_numeric_infix<FInt, FDouble>(
     lhs: &Literal,
     rhs: &Literal,
     int_op: FInt,
diff --git a/src/main.rs b/src/main.rs
index 21ee077..b9e3f44 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,14 +1,61 @@
+mod cell;
 mod evaluator;
 mod parser;
 mod tokenizer;
 
 use std::io;
 
-fn main() {
-    let mut input = String::new();
-    io::stdin().read_line(&mut input).expect("Expected input.");
+use crate::{cell::CellRef, evaluator::Evaluator};
 
-    let mut ast = parser::parse(&input).unwrap();
-    println!("{}", ast.pretty());
-    println!("{}", evaluator::_evaluate(&mut ast).unwrap());
+fn main() {
+    // let mut input = String::new();
+    // io::stdin().read_line(&mut input).expect("Expected input.");
+
+    // let mut ast = parser::parse(&input).unwrap();
+    // println!("{}", ast.pretty());
+    let mut evaluator = Evaluator::new();
+    // // println!("{}", evaluator.evaluate(input).unwrap());
+    // let a1 = CellRef { row: 1, col: 2 };
+    // evaluator.set_cell(a1, input).unwrap();
+    // println!("{:?}", evaluator.get_cell(a1).unwrap());
+
+    println!("CMDS : set <cell_ref>, get <cell_ref>");
+    loop {
+        let mut input = String::new();
+        io::stdin().read_line(&mut input).expect("Expected input.");
+
+        let cmds = ["set", "get"];
+        let cmd = &input[0..3];
+        if !cmds.iter().any(|c| c == &cmd) {
+            println!("{} is an invalid command!", cmd);
+            println!("CMDS : set <cell_ref>, get <cell_ref>");
+            continue;
+        }
+
+        let rest = &input[4..];
+        let mut parts = rest.splitn(2, char::is_whitespace);
+
+        let raw_ref = parts.next().unwrap_or("").trim(); // cell reference
+        let raw_str = parts.next().unwrap_or("").trim(); // rest of the string (value)
+        // println!("{} {}", raw_ref, raw_str);
+
+        if let Ok(cell_ref) = CellRef::new(raw_ref.to_owned()) {
+            match cmd {
+                "set" => match evaluator.set_cell(cell_ref, raw_str.to_owned()) {
+                    Ok(_) => println!("Successfully set cell {} to {}.", raw_ref, raw_str),
+                    Err(e) => println!("{}", e),
+                },
+                "get" => match evaluator.get_cell(cell_ref) {
+                    Ok(res) => println!("{:?}", res),
+                    Err(e) => println!("{}", e),
+                },
+                _ => {
+                    continue; // Impossible
+                }
+            }
+        } else {
+            println!("{} is an invalid cell reference!", raw_ref);
+            continue;
+        }
+    }
 }
diff --git a/src/parser.rs b/src/parser.rs
index 4286d4d..c546baf 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -1,19 +1,19 @@
-use crate::tokenizer::*;
+use crate::{cell::CellRef, tokenizer::*};
 use std::fmt;
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum PrefixOp {
     POS,
     NEG,
     NOT,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum PostfixOp {
     PERCENT,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum InfixOp {
     MUL,
     DIV,
@@ -23,10 +23,10 @@ pub enum InfixOp {
     OR,
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, PartialEq, Clone)]
 pub enum Expr {
     Literal(Literal),
-    CellRef(String),
+    CellRef(CellRef),
     Function {
         name: String,
         args: Vec<Expr>,
@@ -86,7 +86,7 @@ impl fmt::Display for Expr {
             Expr::Postfix { op, expr } => write!(f, "({op:?} {expr})"),
             Expr::Infix { op, lhs, rhs } => write!(f, "({lhs} {op:?} {rhs})"),
             Expr::Function { name, args } => write!(f, "{name}({args:?})"),
-            Expr::CellRef(it) => write!(f, "CellRef({it})"),
+            Expr::CellRef(it) => write!(f, "{it:?}"),
         }
     }
 }
@@ -149,7 +149,7 @@ impl Expr {
             Expr::Postfix { op, .. } => format!("Postfix({:?})", op),
             Expr::Infix { op, .. } => format!("Infix({:?})", op),
             Expr::Function { name, .. } => format!("Function({:?})", name),
-            Expr::CellRef(it) => format!("CellRef({:?})", it),
+            Expr::CellRef(it) => format!("{:?}", it),
         }
     }
 }
@@ -218,7 +218,7 @@ pub fn _parse(input: &mut Tokenizer, min_prec: u8) -> Result<Expr, String> {
                     args: args,
                 }
             }
-            _ => Expr::CellRef(id),
+            _ => Expr::CellRef(CellRef::new(id)?),
         },
 
         it => return Err(format!("Parse error: did not expect token {:?}.", it)),