diff --git a/src/ast/helpers.rs b/src/ast/helpers.rs
index a19fadd..5e788a2 100644
--- a/src/ast/helpers.rs
+++ b/src/ast/helpers.rs
@@ -34,6 +34,7 @@ pub fn stmt_expr(expr: Expr) -> Statement {
 
 pub fn define_expr(name: &str, expr: Expr) -> Definition {
     Definition {
+        mutable: false,
         name: name.into(),
         expr,
     }
diff --git a/src/ast/types.rs b/src/ast/types.rs
index 5119c01..dee1b05 100644
--- a/src/ast/types.rs
+++ b/src/ast/types.rs
@@ -52,6 +52,7 @@ pub enum Statement {
 
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
 pub struct Definition {
+    pub mutable: bool,
     pub name: Name,
     pub expr: Expr,
 }
@@ -65,9 +66,15 @@ pub enum Value {
     Boolean(bool),
     Record(Record),
     Vector(Vector),
+    Label(Label),
+    Ref(Ref),
     Closure { env: EnvName, expr: Box<Expr> },
 }
 
+/// A mutable variable.
+#[derive(PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Clone)]
+pub struct Ref(pub u64);
+
 /// An anonymous function.
 #[derive(PartialEq, PartialOrd, Debug, Clone)]
 pub struct Fn {
diff --git a/src/interpret/interpret.rs b/src/interpret/interpret.rs
index 48cd8c0..93c7f0b 100644
--- a/src/interpret/interpret.rs
+++ b/src/interpret/interpret.rs
@@ -12,7 +12,7 @@ pub fn run(
     let env_name = ast::EnvName("global".to_string());
     let mut state = State::new("global".into());
 
-    defs_to_env(program.0, &env_name, &mut state.envs)?;
+    defs_to_env(program.0, &env_name, &mut state)?;
 
     let main = ast::Expr::Value(state.envs.get(&env_name)?.get(&func)?.clone());
 
@@ -39,8 +39,16 @@ fn eval_statement(
 ) -> Result<StatementResult, Error> {
     match statement {
         ast::Statement::Expr(expr) => eval_expr(expr_env, state, expr).map(StatementResult::Result),
-        ast::Statement::Let(ast::Definition { name, expr }) => {
-            let result = eval_expr(expr_env, state, expr)?;
+        ast::Statement::Let(ast::Definition {
+            mutable,
+            name,
+            expr,
+        }) => {
+            let mut result = eval_expr(expr_env, state, expr)?;
+            if *mutable {
+                let reference = state.insert_variable(result);
+                result = ast::Value::Ref(reference);
+            }
             expr_env.insert(name.clone(), result.clone());
             Ok(StatementResult::Result(result))
         }
@@ -142,7 +150,19 @@ fn eval_expr(expr_env: &Env, state: &mut State, expr: &ast::Expr) -> Result<ast:
                         .insert(name.clone(), rhs);
                     eval_expr(expr_env, state, &ast::UNIT)
                 }
+
+                /*
                 // access via labels
+                ast::Expr::Access { expr, field } => {
+                    let rhs = eval_expr(expr_env, state, rhs)?;
+                    if let Some(mut nested_field) =
+                        access_nested_field(expr_env, state, expr, field)?
+                    {
+                        todo!()
+                    } else {
+                        todo!() // error nested field unreachable
+                    }
+                } */
                 _ => todo!(),
             },
             _ => {
@@ -153,17 +173,45 @@ fn eval_expr(expr_env: &Env, state: &mut State, expr: &ast::Expr) -> Result<ast:
         },
     }
 }
+/*
+fn access_nested_field<'a>(
+    expr_env_name: &Env,
+    state: &'a mut State,
+    expr: &ast::Expr,
+    label: &ast::Label,
+) -> Result<&'a mut ast::Value, Error> {
+    //let lhs = eval_expr(expr_env, state, expr)?;
+    match expr {
+        ast::Expr::Var(var) => {
+            if let Some(mut value) = state.envs.get(&expr_env.name)?.get(&var)? {
+                match &value {
+                    &ast::Value::Record(record) => {
+                        record.
+                    }
+                    _ => todo!(),
+                }
+            }
+        }
+        _ => todo!(),
+    }
+}
+*/
 
 fn defs_to_env(
     defs: Vec<ast::Definition>,
     env_name: &ast::EnvName,
-    envs: &mut Envs,
+    state: &mut State,
 ) -> Result<(), Error> {
     let mut env = Env::new(env_name.clone());
 
     for def in defs {
-        let (name, closure) = match def {
-            ast::Definition { expr, name } => (
+        let (mutable, name, closure) = match def {
+            ast::Definition {
+                mutable,
+                expr,
+                name,
+            } => (
+                mutable,
                 name,
                 ast::Value::Closure {
                     expr: Box::new(expr.clone()),
@@ -171,10 +219,15 @@ fn defs_to_env(
                 },
             ),
         };
-        env.insert_nodup(&name, closure)?;
+        if mutable {
+            let reference = state.insert_variable(closure);
+            env.insert_nodup(&name, ast::Value::Ref(reference))?;
+        } else {
+            env.insert_nodup(&name, closure)?;
+        }
     }
 
-    envs.0.insert(env_name.clone(), env);
+    state.envs.0.insert(env_name.clone(), env);
     Ok(())
 }
 
diff --git a/src/interpret/types.rs b/src/interpret/types.rs
index 73c59c8..b20f27a 100644
--- a/src/interpret/types.rs
+++ b/src/interpret/types.rs
@@ -2,6 +2,7 @@
 
 use crate::ast;
 use std::collections::BTreeMap;
+use std::collections::HashMap;
 
 #[derive(PartialEq, Debug, thiserror::Error)]
 pub enum Error {
@@ -51,23 +52,35 @@ impl Namer {
 
 pub struct State {
     pub name: String,
-    namer: Namer,
+    env_namer: Namer,
     pub envs: Envs,
+    variable_namer: Namer,
+    pub variables: Variables,
 }
 
+pub struct Variables(pub HashMap<ast::Ref, ast::Value>);
+
 impl State {
     pub fn new(name: String) -> State {
         State {
             name,
-            namer: Namer::new(),
+            env_namer: Namer::new(),
             envs: Envs(BTreeMap::new()),
+            variable_namer: Namer::new(),
+            variables: Variables(HashMap::new()),
         }
     }
     pub fn generate_env(&mut self, env: Env) -> Result<ast::EnvName, Error> {
-        let env_name = ast::EnvName(format!("{}_{}", self.name, self.namer.next()));
+        let env_name = ast::EnvName(format!("{}_{}", self.name, self.env_namer.next()));
         self.envs.insert(&env_name, env)?;
         Ok(env_name)
     }
+
+    pub fn insert_variable(&mut self, value: ast::Value) -> ast::Ref {
+        let name = ast::Ref(self.variable_namer.next());
+        self.variables.0.insert(name.clone(), value);
+        name
+    }
 }
 
 #[derive(PartialEq, Debug, Clone)]
diff --git a/src/parser/parser.rs b/src/parser/parser.rs
index ed229d0..8eacc90 100644
--- a/src/parser/parser.rs
+++ b/src/parser/parser.rs
@@ -45,20 +45,13 @@ fn parse_set(tokens: &mut Tokens) -> ParseResult<ast::Expr> {
 }
 
 fn parse_dot(tokens: &mut Tokens, expr: ast::Expr) -> Result<ast::Expr, Error> {
-    if let Some(_dot) = tokens.next_if(&Token::Dot) {
-        if let Some(labels) = tokens.many_sep_by(&Token::Dot, parse_identifier_label)? {
-            Ok(labels
-                .into_iter()
-                .fold(expr, |acc, label| ast::Expr::Access {
-                    expr: Box::new(acc),
-                    field: label,
-                }))
-        } else {
-            Err(Error::UnexpectedToken {
-                expected: Token::Dot,
-                got: tokens.next(),
-            })
-        }
+    if let Some(labels) = tokens.many(parse_label)? {
+        Ok(labels
+            .into_iter()
+            .fold(expr, |acc, label| ast::Expr::Access {
+                expr: Box::new(acc),
+                field: label,
+            }))
     } else {
         Ok(expr)
     }
@@ -66,9 +59,17 @@ fn parse_dot(tokens: &mut Tokens, expr: ast::Expr) -> Result<ast::Expr, Error> {
 
 fn parse_definition(tokens: &mut Tokens) -> ParseResult<ast::Definition> {
     if let Some(_) = tokens.next_if(&Token::Let) {
+        let mutable = match tokens.next_if(&Token::Mut) {
+            Some(_) => true,
+            _ => false,
+        };
         if let Some(name) = parse_identifier_name(tokens)? {
             if let Some(expr) = parse_set(tokens)? {
-                Ok(Some(ast::Definition { name, expr }))
+                Ok(Some(ast::Definition {
+                    mutable,
+                    name,
+                    expr,
+                }))
             } else {
                 Err(Error::UnexpectedToken {
                     expected: Token::Equals,
@@ -220,7 +221,7 @@ fn parse_vector(tokens: &mut Tokens) -> ParseResult<ast::Expr> {
 }
 
 fn parse_record_field_expr(tokens: &mut Tokens) -> ParseResult<(ast::Label, ast::Expr)> {
-    if let Some(label) = parse_identifier_label(tokens)? {
+    if let Some(label) = parse_label(tokens)? {
         if let Some(_) = tokens.next_if(&Token::Colon) {
             if let Some(expr) = parse_expr(tokens)? {
                 Ok(Some((label, expr)))
@@ -277,8 +278,16 @@ fn parse_identifier_name(tokens: &mut Tokens) -> ParseResult<ast::Name> {
     Ok(parse_identifier_string(tokens)?.map(|string| ast::Name(string)))
 }
 
-fn parse_identifier_label(tokens: &mut Tokens) -> ParseResult<ast::Label> {
-    Ok(parse_identifier_string(tokens)?.map(|string| ast::Label(string)))
+fn parse_label(tokens: &mut Tokens) -> ParseResult<ast::Label> {
+    if let Some(LocatedToken {
+        token: Token::Label(string),
+        ..
+    }) = tokens.next_if(&Token::Label("".into()))
+    {
+        Ok(Some(ast::Label(string)))
+    } else {
+        Ok(None)
+    }
 }
 
 fn parse_identifier_string(tokens: &mut Tokens) -> ParseResult<String> {
@@ -335,7 +344,7 @@ mod tests {
     }
     #[test]
     fn record() {
-        let program = "{ hello: 17, hi: \"cool\"}".to_string();
+        let program = "{ .hello: 17, .hi: \"cool\"}".to_string();
         let result = parse(&mut scan(program), parse_expr);
         insta::assert_debug_snapshot!(result);
     }
@@ -353,7 +362,7 @@ mod tests {
     }
     #[test]
     fn assign() {
-        let program = "x = [2, { hello: 7 }];".to_string();
+        let program = "x = [2, { .hello: 7 }];".to_string();
         let result = parse(&mut scan(program), parse_expr);
         insta::assert_debug_snapshot!(result);
     }
@@ -382,11 +391,17 @@ mod tests {
         insta::assert_debug_snapshot!(result);
     }
     #[test]
+    fn let_mut_number() {
+        let program = "let mut x = 108;".to_string();
+        let result = parse(&mut scan(program), parse_definition);
+        insta::assert_debug_snapshot!(result);
+    }
+    #[test]
     fn full_program() {
         let program = "
 let init = fn() {
   return {
-    player: { position: { x: 10, y: 20 }, },
+    .player: { .position: { .x: 10, .y: 20 }, },
   };
 };
 
@@ -399,7 +414,7 @@ let draw = fn(frame, state) {
 };
 
 let migrate = fn(state) {
-    return { player: { pos: state.player.position } };
+    return { .player: { .pos: state.player.position } };
 };
 "
         .to_string();
diff --git a/src/parser/scanner.rs b/src/parser/scanner.rs
index 392a34a..a4eb480 100644
--- a/src/parser/scanner.rs
+++ b/src/parser/scanner.rs
@@ -11,11 +11,6 @@ pub fn scan(source: String) -> Tokens {
         let start = scanner.cursor();
         if let Some(c) = scanner.pop() {
             match *c {
-                '.' => tokens.push(LocatedToken {
-                    start,
-                    end: scanner.cursor(),
-                    token: Token::Dot,
-                }),
                 ',' => tokens.push(LocatedToken {
                     start,
                     end: scanner.cursor(),
@@ -66,6 +61,31 @@ pub fn scan(source: String) -> Tokens {
                     end: scanner.cursor(),
                     token: Token::Equals,
                 }),
+                // labels
+                '.' => {
+                    let mut str = "".to_string();
+                    loop {
+                        if let Some(ch) = scanner.peek()
+                            && !ch.is_alphanumeric()
+                            && *ch != '_'
+                        {
+                            break;
+                        }
+                        if let Some(ch) = scanner.pop() {
+                            str.push(*ch);
+                        } else {
+                            break;
+                        }
+                    }
+
+                    tokens.push(LocatedToken {
+                        start,
+                        end: scanner.cursor(),
+                        token: match str.as_str() {
+                            _ => Token::Label(str),
+                        },
+                    });
+                }
                 // comments
                 '#' => {
                     let mut str = "".to_string();
@@ -91,6 +111,7 @@ pub fn scan(source: String) -> Tokens {
                         token: Token::String(str),
                     });
                 }
+                // whitespace
                 _ if c.is_whitespace() => {}
                 // numbers
                 _ if c.is_numeric() => {
@@ -137,6 +158,7 @@ pub fn scan(source: String) -> Tokens {
                         token: match str.as_str() {
                             "fn" => Token::Fn,
                             "let" => Token::Let,
+                            "mut" => Token::Mut,
                             "return" => Token::Return,
                             "true" => Token::True,
                             "false" => Token::False,
diff --git a/src/parser/snapshots/ayin__parser__parser__tests__full_program.snap b/src/parser/snapshots/ayin__parser__parser__tests__full_program.snap
index 9155220..07b80cb 100644
--- a/src/parser/snapshots/ayin__parser__parser__tests__full_program.snap
+++ b/src/parser/snapshots/ayin__parser__parser__tests__full_program.snap
@@ -5,6 +5,7 @@ expression: result
 Ok(
     [
         Definition {
+            mutable: false,
             name: Name(
                 "init",
             ),
@@ -65,6 +66,7 @@ Ok(
             ),
         },
         Definition {
+            mutable: false,
             name: Name(
                 "update",
             ),
@@ -99,6 +101,7 @@ Ok(
             ),
         },
         Definition {
+            mutable: false,
             name: Name(
                 "draw",
             ),
@@ -155,6 +158,7 @@ Ok(
             ),
         },
         Definition {
+            mutable: false,
             name: Name(
                 "migrate",
             ),
diff --git a/src/parser/snapshots/ayin__parser__parser__tests__let_mut_number.snap b/src/parser/snapshots/ayin__parser__parser__tests__let_mut_number.snap
new file mode 100644
index 0000000..4ef1919
--- /dev/null
+++ b/src/parser/snapshots/ayin__parser__parser__tests__let_mut_number.snap
@@ -0,0 +1,17 @@
+---
+source: src/parser/parser.rs
+expression: result
+---
+Ok(
+    Definition {
+        mutable: true,
+        name: Name(
+            "x",
+        ),
+        expr: Value(
+            Int(
+                108,
+            ),
+        ),
+    },
+)
diff --git a/src/parser/snapshots/ayin__parser__parser__tests__let_number.snap b/src/parser/snapshots/ayin__parser__parser__tests__let_number.snap
index 8dc972a..087a843 100644
--- a/src/parser/snapshots/ayin__parser__parser__tests__let_number.snap
+++ b/src/parser/snapshots/ayin__parser__parser__tests__let_number.snap
@@ -4,6 +4,7 @@ expression: result
 ---
 Ok(
     Definition {
+        mutable: false,
         name: Name(
             "x",
         ),
diff --git a/src/parser/snapshots/ayin__parser__scanner__tests__let_fn.snap b/src/parser/snapshots/ayin__parser__scanner__tests__let_fn.snap
index 3ad6382..a5f797a 100644
--- a/src/parser/snapshots/ayin__parser__scanner__tests__let_fn.snap
+++ b/src/parser/snapshots/ayin__parser__scanner__tests__let_fn.snap
@@ -18,8 +18,7 @@ expression: result
     Identifier(
         "console",
     ),
-    Dot,
-    Identifier(
+    Label(
         "log",
     ),
     OpenParen,
diff --git a/src/parser/snapshots/ayin__parser__scanner__tests__scaffolding.snap b/src/parser/snapshots/ayin__parser__scanner__tests__scaffolding.snap
index 245b69f..28ceab5 100644
--- a/src/parser/snapshots/ayin__parser__scanner__tests__scaffolding.snap
+++ b/src/parser/snapshots/ayin__parser__scanner__tests__scaffolding.snap
@@ -88,8 +88,7 @@ expression: result
     Identifier(
         "frame",
     ),
-    Dot,
-    Identifier(
+    Label(
         "clear",
     ),
     OpenParen,
@@ -134,12 +133,10 @@ expression: result
     Identifier(
         "state",
     ),
-    Dot,
-    Identifier(
+    Label(
         "player",
     ),
-    Dot,
-    Identifier(
+    Label(
         "position",
     ),
     CloseCurly,
diff --git a/src/parser/types.rs b/src/parser/types.rs
index 232116f..7b9d9e4 100644
--- a/src/parser/types.rs
+++ b/src/parser/types.rs
@@ -9,6 +9,7 @@ pub struct LocatedToken {
 pub enum Token {
     Let,
     Fn,
+    Mut,
     Return,
     Equals,
     OpenParen,
@@ -17,7 +18,6 @@ pub enum Token {
     CloseBracket,
     OpenCurly,
     CloseCurly,
-    Dot,
     Comma,
     Semicolon,
     Colon,
@@ -26,6 +26,7 @@ pub enum Token {
     Number(u32),
     String(String),
     Identifier(String),
+    Label(String),
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -52,6 +53,7 @@ impl Tokens {
             (Token::Identifier(_), Token::Identifier(_)) => true,
             (Token::Number(_), Token::Number(_)) => true,
             (Token::String(_), Token::String(_)) => true,
+            (Token::Label(_), Token::Label(_)) => true,
             _ => false,
         })
     }