diff --git a/src/ast.rs b/src/ast.rs
index e25f4db..f659909 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -192,4 +192,4 @@ impl AstNode {
     pub fn null() -> AstNode {
         AstNode::Null
     }
-}
\ No newline at end of file
+}
diff --git a/src/lib.rs b/src/lib.rs
index 8f51669..ff4fdb0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,7 +10,7 @@ pub fn compile(source: &str) -> Vec<u8> {
 
 pub fn compile_wat(source: &str) -> String {
     // let mut s = SymbolGenerator::new();
-    let ast = parse::interpret(source);
+    let ast = parse::run(source);
     // println!("{:?}", ast);
     unimplemented!()
     // let wasm = ast.emit(&mut s);
diff --git a/src/main.rs b/src/main.rs
index cd7c8a4..b32e4f6 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -5,7 +5,7 @@ fn main() -> std::io::Result<()> {
     // Read the source from a file.
     let source = std::fs::read_to_string("test.pvt").unwrap();
     // Compile it
-    let _value = pivot::parse::interpret(&source);
+    let _value = pivot::parse::run(&source);
     // let binary = pivot::compile(&source);
     // Write it to a file.
     // File::create("out.wasm")?.write_all(&binary)?;
diff --git a/src/parse.rs b/src/parse.rs
index 0231f0e..8614e84 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -4,11 +4,16 @@ pub enum Token {
     Float(f64),
     String(String),
     Boolean(bool),
+    Identifier(String),
+    Keyword(String),
+    Comma,
     Plus,
     Minus,
     Star,
     Slash,
     Bang,
+    Equals,
+    Semicolon,
     Quote(char),
     Parenthesis { closing: bool },
     Whitespace(String),
@@ -19,8 +24,21 @@ pub enum Token {
 pub enum InterpreterError {
     /// Error parsing source
     ParseError(String),
+    /// Unexpected token
+    UnexpectedToken,
+    /// Mismatched types
+    MismatchedTypes,
+    /// Type error
+    TypeError,
     /// Unexpected EOF
     UnexpectedEOF,
+    /// Expected value
+    ExpectedValue,
+}
+impl<T> From<Option<T>> for InterpreterError {
+    fn from(value: Option<T>) -> InterpreterError {
+        InterpreterError::ExpectedValue
+    }
 }
 
 pub fn tokenize(source: &str) -> Result<Vec<Token>, InterpreterError> {
@@ -37,18 +55,37 @@ pub fn tokenize(source: &str) -> Result<Vec<Token>, InterpreterError> {
         if chars_consumed == 0 {
             Err(())
         } else if current_value.contains(".") {
-            Ok((Token::Float(current_value.parse::<f64>().unwrap()), chars_consumed))
+            Ok((
+                Token::Float(current_value.parse::<f64>().unwrap()),
+                chars_consumed,
+            ))
         } else {
-            Ok((Token::Integer(current_value.parse::<i64>().unwrap()), chars_consumed))
+            Ok((
+                Token::Integer(current_value.parse::<i64>().unwrap()),
+                chars_consumed,
+            ))
         }
     }
-    fn tokenize_bool(chars: &[char]) -> Result<(Token, usize), ()> {
-        if chars.len() >= 5 && chars[0..5] == ['f', 'a', 'l', 's', 'e'] {
-            Ok((Token::Boolean(false), 5))
-        } else if chars.len() >= 4 && chars[0..4] == ['t', 'r', 'u', 'e'] {
-            Ok((Token::Boolean(true), 4))
+    fn tokenize_identifier(chars: &[char]) -> Result<(Token, usize), ()> {
+        let mut current_value = String::new();
+        let mut chars_consumed = 0;
+        if chars[chars_consumed].is_alphabetic() {
+            current_value.push(chars[chars_consumed]);
         } else {
-            Err(())
+            return Err(());
+        }
+        chars_consumed += 1;
+        while chars_consumed < chars.len()
+            && (chars[chars_consumed].is_alphanumeric() || chars[chars_consumed] == '_')
+        {
+            current_value.push(chars[chars_consumed]);
+            chars_consumed += 1;
+        }
+        match &current_value[..] {
+            "true" => Ok((Token::Boolean(true), 4)),
+            "false" => Ok((Token::Boolean(false), 5)),
+            "let" => Ok((Token::Keyword(current_value), chars_consumed)),
+            _ => Ok((Token::Identifier(current_value), chars_consumed)),
         }
     }
     fn tokenize_string(chars: &[char]) -> Result<(Token, usize), ()> {
@@ -103,6 +140,8 @@ pub fn tokenize(source: &str) -> Result<Vec<Token>, InterpreterError> {
             Ok((Token::Slash, 1))
         } else if chars[0] == '!' {
             Ok((Token::Bang, 1))
+        } else if chars[0] == '=' {
+            Ok((Token::Equals, 1))
         } else {
             Err(())
         }
@@ -121,12 +160,18 @@ pub fn tokenize(source: &str) -> Result<Vec<Token>, InterpreterError> {
         } else if let Ok((num, chars_consumed)) = tokenize_string(&source[index..]) {
             tokens.push(num);
             index += chars_consumed;
-        } else if let Ok((num, chars_consumed)) = tokenize_bool(&source[index..]) {
+        } else if let Ok((num, chars_consumed)) = tokenize_identifier(&source[index..]) {
             tokens.push(num);
             index += chars_consumed;
         } else if let Ok((operator, chars_consumed)) = tokenize_operator(&source[index..]) {
             tokens.push(operator);
             index += chars_consumed;
+        } else if source[index] == ',' {
+            tokens.push(Token::Comma);
+            index += 1;
+        } else if source[index] == ';' {
+            tokens.push(Token::Semicolon);
+            index += 1;
         } else if source[index] == '(' {
             tokens.push(Token::Parenthesis { closing: false });
             index += 1;
@@ -147,18 +192,53 @@ pub enum AstPrimitive {
     Float(f64),
     String(String),
     Boolean(bool),
+    Identifier(String),
+    Null,
+}
+impl std::hash::Hash for AstPrimitive {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        match self {
+            AstPrimitive::Float(f) => format!("{}", f).hash(state),
+            _ => self.hash(state),
+        }
+    }
 }
 
 #[derive(Clone, PartialEq, Debug)]
 pub enum AstNode {
     Primitive(AstPrimitive),
-    Negate { body: Box<AstNode> },
-    Add { left: Box<AstNode>, right: Box<AstNode> },
-    Subtract { left: Box<AstNode>, right: Box<AstNode> },
-    Multiply { left: Box<AstNode>, right: Box<AstNode> },
-    Divide { left: Box<AstNode>, right: Box<AstNode> },
+    Negate {
+        body: Box<AstNode>,
+    },
+    Add {
+        left: Box<AstNode>,
+        right: Box<AstNode>,
+    },
+    Subtract {
+        left: Box<AstNode>,
+        right: Box<AstNode>,
+    },
+    Multiply {
+        left: Box<AstNode>,
+        right: Box<AstNode>,
+    },
+    Divide {
+        left: Box<AstNode>,
+        right: Box<AstNode>,
+    },
+    Declare {
+        identifier: String,
+    },
+    Assign {
+        left: Box<AstNode>,
+        right: Box<AstNode>,
+    },
+    Program {
+        statements: Vec<AstNode>,
+    },
     Null,
 }
+
 pub fn parse(tokens: &[Token]) -> Result<AstNode, InterpreterError> {
     fn parse_primary_expression(tokens: &[Token]) -> Result<(AstNode, usize), InterpreterError> {
         if tokens.is_empty() {
@@ -171,8 +251,23 @@ pub fn parse(tokens: &[Token]) -> Result<AstNode, InterpreterError> {
             Ok((AstNode::Primitive(AstPrimitive::Boolean(*n)), 1))
         } else if let Token::String(s) = &tokens[0] {
             Ok((AstNode::Primitive(AstPrimitive::String(s.clone())), 1))
+        } else if let Token::Identifier(s) = &tokens[0] {
+            Ok((AstNode::Primitive(AstPrimitive::Identifier(s.clone())), 1))
+        } else if tokens[0] == Token::Keyword("let".to_owned()) {
+            if tokens.len() < 2 {
+                Err(InterpreterError::UnexpectedEOF)
+            } else if let Token::Identifier(s) = &tokens[1] {
+                Ok((
+                    AstNode::Declare {
+                        identifier: s.clone(),
+                    },
+                    2,
+                ))
+            } else {
+                Err(InterpreterError::UnexpectedToken)
+            }
         } else {
-            Err(InterpreterError::ParseError("Expected literal".to_owned()))
+            Err(InterpreterError::UnexpectedToken)
         }
     }
     fn parse_grouped_expression(tokens: &[Token]) -> Result<(AstNode, usize), InterpreterError> {
@@ -188,7 +283,9 @@ pub fn parse(tokens: &[Token]) -> Result<AstNode, InterpreterError> {
         index += tokens_consumed;
         // ')'
         if !matches!(tokens[index], Token::Parenthesis { closing: true }) {
-            return Err(InterpreterError::ParseError("No closing parenthesis".to_owned()));
+            return Err(InterpreterError::ParseError(
+                "No closing parenthesis".to_owned(),
+            ));
         } else {
             index += 1;
         }
@@ -205,15 +302,21 @@ pub fn parse(tokens: &[Token]) -> Result<AstNode, InterpreterError> {
             index += tokens_consumed;
             Ok((
                 match operation {
-                    Token::Minus => AstNode::Negate { body: Box::new(body) },
-                    Token::Bang => AstNode::Negate { body: Box::new(body) },
+                    Token::Minus => AstNode::Negate {
+                        body: Box::new(body),
+                    },
+                    Token::Bang => AstNode::Negate {
+                        body: Box::new(body),
+                    },
                     _ => return Err(InterpreterError::ParseError("Impossible".to_owned())),
                 },
-                index
+                index,
             ))
         }
     }
-    fn parse_multiplication_expression(tokens: &[Token]) -> Result<(AstNode, usize), InterpreterError> {
+    fn parse_multiplication_expression(
+        tokens: &[Token],
+    ) -> Result<(AstNode, usize), InterpreterError> {
         let mut index = 0;
         let (mut value, tokens_consumed) = parse_unary_expression(&tokens[index..])?;
         index += tokens_consumed;
@@ -265,117 +368,208 @@ pub fn parse(tokens: &[Token]) -> Result<AstNode, InterpreterError> {
         }
         Ok((value, index))
     }
+    fn parse_assign_expression(tokens: &[Token]) -> Result<(AstNode, usize), InterpreterError> {
+        let mut index = 0;
+        let (identifier, tokens_consumed) = parse_addition_expression(&tokens[index..])?;
+        index += tokens_consumed;
+        if index < tokens.len() && tokens[index] == Token::Equals {
+            index += 1;
+        } else {
+            return Ok((identifier, index));
+        }
+        let (value, tokens_consumed) = parse_addition_expression(&tokens[index..])?;
+        index += tokens_consumed;
+        Ok((
+            AstNode::Assign {
+                left: Box::new(identifier),
+                right: Box::new(value),
+            },
+            index,
+        ))
+    }
     fn parse_expression(tokens: &[Token]) -> Result<(AstNode, usize), InterpreterError> {
-        parse_addition_expression(tokens)
+        parse_assign_expression(tokens)
     }
-    let (ast, _) = parse_expression(tokens)?;
-    Ok(ast)
+    let mut statements = vec![];
+    let mut index = 0;
+    loop {
+        if index >= tokens.len() {
+            break;
+        }
+        let statement = parse_expression(&tokens[index..]);
+        if let Ok((statement, tokens_consumed)) = statement {
+            statements.push(statement);
+            index += tokens_consumed;
+        } else {
+            break;
+        }
+    }
+    Ok(AstNode::Program { statements })
 }
-pub fn evaluate(ast: &AstNode) -> Result<AstPrimitive, InterpreterError> {
-    use std::mem::discriminant;
+pub fn interpret(ast: &AstNode) -> Result<(), InterpreterError> {
+    use std::{collections::HashMap, mem::discriminant};
     use AstNode::*;
-    match ast {
-        Primitive(p) => Ok(p.clone()),
-        Negate { body } => {
-            if let AstPrimitive::Integer(body) = evaluate(body)? {
-                Ok(AstPrimitive::Integer(body * -1))
-            } else if let AstPrimitive::Boolean(body) = evaluate(body)? {
-                Ok(AstPrimitive::Boolean(!body))
-            }else {
-                Err(InterpreterError::ParseError("Can only negate integers and bools".to_owned()))
-            }
-        },
-        Add { left, right } => {
-            let left = evaluate(left)?;
-            let right = evaluate(right)?;
-            if discriminant(&left) != discriminant(&right) {
-                Err(InterpreterError::ParseError("Mismatched types".to_owned()))
-            } else {
-                if let AstPrimitive::Integer(left) = left {
-                    if let AstPrimitive::Integer(right) = right {
-                       return Ok(AstPrimitive::Integer(left + right));
-                    }
-                }
-                if let AstPrimitive::Float(left) = left {
-                    if let AstPrimitive::Float(right) = right {
-                       return Ok(AstPrimitive::Float(left + right));
-                    }
-                }
-                if let AstPrimitive::String(left) = left {
-                    if let AstPrimitive::String(right) = right {
-                       return Ok(AstPrimitive::String(format!("{}{}", left, right)));
-                    }
-                }
-                Err(InterpreterError::ParseError("Can only add integers, strings, and floats".to_owned()))
-            }
+    let mut vars: HashMap<String, Option<AstPrimitive>> = HashMap::new();
+    if let Program { statements } = ast {
+        for statement in statements {
+            let _ = interpret_statement(statement, &mut vars)?;
         }
-        Subtract { left, right } => {
-            let left = evaluate(left)?;
-            let right = evaluate(right)?;
-            if discriminant(&left) != discriminant(&right) {
-                Err(InterpreterError::ParseError("Mismatched types".to_owned()))
-            } else {
-                if let AstPrimitive::Integer(left) = left {
-                    if let AstPrimitive::Integer(right) = right {
-                       return Ok(AstPrimitive::Integer(left - right));
-                    }
-                }
-                if let AstPrimitive::Float(left) = left {
-                    if let AstPrimitive::Float(right) = right {
-                       return Ok(AstPrimitive::Float(left - right));
-                    }
-                }
-                Err(InterpreterError::ParseError("Can only subtract integers and floats".to_owned()))
-            }
-        }
-        Multiply { left, right } => {
-            let left = evaluate(left)?;
-            let right = evaluate(right)?;
-            if discriminant(&left) != discriminant(&right) {
-                Err(InterpreterError::ParseError("Mismatched types".to_owned()))
-            } else {
-                if let AstPrimitive::Integer(left) = left {
-                    if let AstPrimitive::Integer(right) = right {
-                       return Ok(AstPrimitive::Integer(left * right));
-                    }
-                }
-                if let AstPrimitive::Float(left) = left {
-                    if let AstPrimitive::Float(right) = right {
-                       return Ok(AstPrimitive::Float(left * right));
-                    }
-                }
-                Err(InterpreterError::ParseError("Can only multiply integers and floats".to_owned()))
-            }
-        }
-        Divide { left, right } => {
-            let left = evaluate(left)?;
-            let right = evaluate(right)?;
-            if discriminant(&left) != discriminant(&right) {
-                Err(InterpreterError::ParseError("Mismatched types".to_owned()))
-            } else {
-                if let AstPrimitive::Integer(left) = left {
-                    if let AstPrimitive::Integer(right) = right {
-                       return Ok(AstPrimitive::Integer(left / right));
-                    }
-                }
-                if let AstPrimitive::Float(left) = left {
-                    if let AstPrimitive::Float(right) = right {
-                       return Ok(AstPrimitive::Float(left / right));
-                    }
-                }
-                Err(InterpreterError::ParseError("Can only divide integers and floats".to_owned()))
-            }
-        }
-        Null => Err(InterpreterError::ParseError("Cannot evaluate null".to_owned())),
     }
+    fn interpret_statement(
+        ast: &AstNode,
+        vars: &mut HashMap<String, Option<AstPrimitive>>,
+    ) -> Result<Option<AstPrimitive>, InterpreterError> {
+        match ast {
+            Primitive(p) => {
+                if let AstPrimitive::Identifier(id) = p {
+                    if let Some(val) = vars.get(id) {
+                        if let Some(val) = val {
+                            Ok(Some(val.clone()))
+                        } else {
+                            Err(InterpreterError::ParseError(
+                                "Variable used before definition".to_owned(),
+                            ))
+                        }
+                    } else {
+                        Err(InterpreterError::ParseError(
+                            "Variable used before declaration".to_owned(),
+                        ))
+                    }
+                } else {
+                    Ok(Some(p.clone()))
+                }
+            }
+            Negate { body } => {
+                if let Some(AstPrimitive::Integer(body)) = interpret_statement(body, vars)? {
+                    Ok(Some(AstPrimitive::Integer(body * -1)))
+                } else if let Some(AstPrimitive::Boolean(body)) = interpret_statement(body, vars)? {
+                    Ok(Some(AstPrimitive::Boolean(!body)))
+                } else {
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            Declare { identifier } => {
+                vars.insert(identifier.clone(), None);
+                Ok(None)
+            }
+            Assign { left, right } => {
+                if let AstNode::Declare { identifier } = Box::leak(left.clone()) {
+                    let _ = interpret(left)?;
+                    let value = interpret_statement(right, vars)?;
+                    vars.insert(identifier.clone(), value);
+                    Ok(Some(vars.get(identifier).unwrap().clone().unwrap().clone()))
+                } else if let AstNode::Primitive(AstPrimitive::Identifier(id)) =
+                    Box::leak(left.clone())
+                {
+                    let id = id.clone();
+                    let value = interpret_statement(right, vars)?;
+                    vars.insert(id.clone(), value);
+                    Ok(Some(vars.get(&id).unwrap().clone().unwrap().clone()))
+                } else {
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            Add { left, right } => {
+                let left =
+                    interpret_statement(left, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                let right =
+                    interpret_statement(right, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                if discriminant(&left) != discriminant(&right) {
+                    Err(InterpreterError::MismatchedTypes)
+                } else {
+                    if let AstPrimitive::Integer(left) = left {
+                        if let AstPrimitive::Integer(right) = right {
+                            return Ok(Some(AstPrimitive::Integer(left + right)));
+                        }
+                    }
+                    if let AstPrimitive::Float(left) = left {
+                        if let AstPrimitive::Float(right) = right {
+                            return Ok(Some(AstPrimitive::Float(left + right)));
+                        }
+                    }
+                    if let AstPrimitive::String(left) = left {
+                        if let AstPrimitive::String(right) = right {
+                            return Ok(Some(AstPrimitive::String(format!("{}{}", left, right))));
+                        }
+                    }
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            Subtract { left, right } => {
+                let left =
+                    interpret_statement(left, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                let right =
+                    interpret_statement(right, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                if discriminant(&left) != discriminant(&right) {
+                    Err(InterpreterError::MismatchedTypes)
+                } else {
+                    if let AstPrimitive::Integer(left) = left {
+                        if let AstPrimitive::Integer(right) = right {
+                            return Ok(Some(AstPrimitive::Integer(left - right)));
+                        }
+                    }
+                    if let AstPrimitive::Float(left) = left {
+                        if let AstPrimitive::Float(right) = right {
+                            return Ok(Some(AstPrimitive::Float(left - right)));
+                        }
+                    }
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            Multiply { left, right } => {
+                let left =
+                    interpret_statement(left, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                let right =
+                    interpret_statement(right, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                if discriminant(&left) != discriminant(&right) {
+                    Err(InterpreterError::MismatchedTypes)
+                } else {
+                    if let AstPrimitive::Integer(left) = left {
+                        if let AstPrimitive::Integer(right) = right {
+                            return Ok(Some(AstPrimitive::Integer(left * right)));
+                        }
+                    }
+                    if let AstPrimitive::Float(left) = left {
+                        if let AstPrimitive::Float(right) = right {
+                            return Ok(Some(AstPrimitive::Float(left * right)));
+                        }
+                    }
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            Divide { left, right } => {
+                let left =
+                    interpret_statement(left, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                let right =
+                    interpret_statement(right, vars)?.ok_or(InterpreterError::ExpectedValue)?;
+                if discriminant(&left) != discriminant(&right) {
+                    Err(InterpreterError::MismatchedTypes)
+                } else {
+                    if let AstPrimitive::Integer(left) = left {
+                        if let AstPrimitive::Integer(right) = right {
+                            return Ok(Some(AstPrimitive::Integer(left / right)));
+                        }
+                    }
+                    if let AstPrimitive::Float(left) = left {
+                        if let AstPrimitive::Float(right) = right {
+                            return Ok(Some(AstPrimitive::Float(left / right)));
+                        }
+                    }
+                    Err(InterpreterError::TypeError)
+                }
+            }
+            _ => Err(InterpreterError::TypeError),
+        }
+    }
+    Ok(())
 }
-pub fn interpret(source: &str) -> Result<(), InterpreterError> {
+pub fn run(source: &str) -> Result<(), InterpreterError> {
     println!("source: {:?}", source);
     let tokens = tokenize(source);
     println!("tokens: {:?}", tokens);
     let ast = parse(&tokens?);
     println!("ast: {:?}", ast);
-    let value = evaluate(&ast?);
+    let value = interpret(&ast?);
     println!("value: {:?}", value);
     Ok(())
-}
\ No newline at end of file
+}
diff --git a/test.pvt b/test.pvt
index e1c7a7e..eac2de5 100644
--- a/test.pvt
+++ b/test.pvt
@@ -1 +1,2 @@
-"a" + "b"
\ No newline at end of file
+let asdf = 4
+asdf + 1
\ No newline at end of file
diff --git a/test.txt b/test.txt
index 0478b5f..b3985f2 100644
--- a/test.txt
+++ b/test.txt
@@ -10,4 +10,6 @@ MultiplyExpression = UnaryExpression | MultiplyExpression MultiplyOperator Unary
 AddOperator = `+` | `-`
 AddExpression = MultiplyExpression | AddExpression AddOperator MultiplyExpression
 
-Expression = AddExpression
\ No newline at end of file
+AssignExpression = AddExpression | Identifier `=` AddExpression
+
+Expression = AssignExpression
\ No newline at end of file