diff --git a/examples/bf.cxpr b/examples/bf.cxpr
new file mode 100644
index 0000000..36e058b
--- /dev/null
+++ b/examples/bf.cxpr
@@ -0,0 +1,68 @@
+while true {
+    print("bf> ");
+    let program = input();
+    let tape = [0]*256;
+    let ptr = 0;
+    let i = 0;
+    while i < len(program) {
+        let op = program[i];
+        if op == '+' {
+            tape[ptr] += 1;
+            if tape[ptr] >= 256 {
+                tape[ptr] -= 256;
+            }
+        } elif op == '-' {
+            tape[ptr] -= 1;
+            if tape[ptr] < 0 {
+                tape[ptr] += 256;
+            }
+        } elif op == '>' {
+            ptr += 1;
+        } elif op == '<' {
+            ptr -= 1;
+        } elif op == '.' {
+            print(chr(tape[ptr]));
+        } elif op == ',' {
+            tape[ptr] = ord(input()[0]);
+        } elif op == '[' {
+            if tape[ptr] == 0 {
+                let depth = 0;
+                let running = true;
+                while running {
+                    i += 1;
+                    if program[i] == ']' {
+                        if depth == 0 {
+                            running = false;
+                        }
+                        depth -= 1;
+                    } elif program[i] == '[' {
+                        depth += 1;
+                    }
+                }
+            }
+        } elif op == ']' {
+            if tape[ptr] != 0 {
+                let depth = 0;
+                let running = true;
+                while running {
+                    i -= 1;
+                    if program[i] == '[' {
+                        if depth == 0 {
+                            running = false;
+                        }
+                        depth -= 1;
+                    } elif program[i] == ']' {
+                        depth += 1;
+                    }
+                }
+            }
+        }
+
+        if ptr >= len(tape) {
+            tape += [0]*256;
+        }
+
+        i += 1;
+    }
+    println("");
+}
\ No newline at end of file
diff --git a/src/eval.rs b/src/eval.rs
index d733d7e..d021efd 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -123,22 +123,28 @@ pub fn eval_expr(expr: &Expr, env: EnvRef) -> Result<Value, RuntimeError> {
                 => eval_comp(lhs, rhs, op, env),
             o => todo!("{:?}", o) // TODO other operations
         },
+        Expr::Unary { arg, op } => eval_unary(arg, op, env),
         Expr::List { items } => {
             let mut list = Vec::with_capacity(items.len());
             for item in items {
                 list.push(eval_expr(item, env.clone())?);
             }
-            Ok(Value::List(Rc::new(list)))
+            Ok(Value::from(list))
         },
         Expr::FuncCall { func, args, pos } => {
-            let func = eval_expr(&func, env.clone())?;
+            let func = eval_expr(func, env.clone())?;
             let mut arg_values = Vec::with_capacity(args.len());
             for arg in args {
                 let result = eval_expr(arg, env.clone())?;
                 arg_values.push(result);
             }
             func.call(arg_values, pos)
-        }
+        },
+        Expr::Index { lhs, index, pos } => {
+            let l = eval_expr(lhs, env.clone())?;
+            let idx = eval_expr(index, env)?;
+            l.index(&idx).map_err(|e| RuntimeError { message: e, pos: pos.clone() })
+        },
         e => todo!("{:?}", e) // TODO other expression types
     }
 }
@@ -197,6 +203,27 @@ pub fn eval_assignment(lhs: &Box<Expr>, rhs: &Box<Expr>, op: &Token, env: EnvRef
                 .set(name.clone(), result.clone()).expect("unreachable");
             Ok(result)
         }
+    } else if let Expr::Index { lhs, index, pos } = &**lhs {
+        let l = eval_expr(lhs, env.clone())?;
+        let idx = eval_expr(index, env.clone())?;
+        if op.ty == TokenType::Equal {
+            let r = eval_expr(rhs, env)?;
+            l.assign_index(&idx, r.clone()).map_err(|e| RuntimeError { message: e, pos: pos.clone() })?;
+            Ok(r)
+        } else {
+            let prev_value = l.index(&idx).map_err(|e| RuntimeError { message: e, pos: pos.clone() })?;
+            let r = eval_expr(rhs, env)?;
+            let result = match op.ty {
+                TokenType::PlusEqual => &prev_value + &r,
+                TokenType::MinusEqual => &prev_value - &r,
+                TokenType::StarEqual => &prev_value * &r,
+                TokenType::SlashEqual => &prev_value / &r,
+                TokenType::PercentEqual => &prev_value % &r,
+                _ => todo!() // TODO more operations
+            }.map_err(|e| RuntimeError { message: e, pos: op.pos.clone() })?;
+            l.assign_index(&idx, result.clone()).map_err(|e| RuntimeError { message: e, pos: pos.clone() })?;
+            Ok(result)
+        }
     } else {
         unreachable!()
     }
@@ -242,4 +269,12 @@ pub fn eval_comp(lhs: &Box<Expr>, rhs: &Box<Expr>, op: &Token, env: EnvRef) -> R
             .map(|o| Value::from(o as i8)),
         _ => unreachable!()
     }
+}
+
+pub fn eval_unary(arg: &Box<Expr>, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
+    let a = eval_expr(arg, env)?;
+    match op.ty {
+        TokenType::Minus => -a,
+        _ => todo!(),
+    }.map_err(|e| RuntimeError { message: e, pos: op.pos.clone() })
 }
\ No newline at end of file
diff --git a/src/expr.rs b/src/expr.rs
index 632d41c..8a973d4 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -27,7 +27,8 @@ pub enum Expr {
     Ident { value: Token },
     Literal { value: Token },
     List { items: Vec<Expr> },
-    FuncCall { func: Box<Expr>, args: Vec<Expr>, pos: Position }
+    FuncCall { func: Box<Expr>, args: Vec<Expr>, pos: Position },
+    Index { lhs: Box<Expr>, index: Box<Expr>, pos: Position },
 }
 
 impl fmt::Debug for Expr {
@@ -39,13 +40,14 @@ impl fmt::Debug for Expr {
             Self::Literal { value } => write!(f, "(lit {:?})", value),
             Self::List { items } => write!(f, "(list {:?})", items),
             Self::FuncCall { func, args, .. } => write!(f, "(call {:?} {:?})", func, args),
+            Self::Index { lhs, index, .. } => write!(f, "(index {:?} {:?})", lhs, index),
         }
     }
 }
 
 impl Expr {
     pub fn is_lvalue(&self) -> bool {
-        matches!(self, Expr::Ident{..})
+        return matches!(self, Expr::Ident{..} | Expr::Index{..})
     }
 
     pub fn is_assignment(&self) -> bool {
diff --git a/src/parser.rs b/src/parser.rs
index 41fec52..7a00483 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -289,14 +289,31 @@ impl Parser {
     }
 
     fn fncall(&mut self) -> Result<Expr, ParserError> {
-        let expr = self.expr_base()?;
-        if !self.at_end() && self.peek().ty == TokenType::LParen {
-            let lparen = self.next();
-            let args = self.commalist(TokenType::RParen, Self::assignment)?;
-            Ok(Expr::FuncCall { func: Box::new(expr), args, pos: lparen.pos.clone() })
-        } else {
-            Ok(expr)
+        let mut expr = self.expr_base()?;
+        while !self.at_end() {
+            match self.peek().ty {
+                TokenType::LParen => expr = self.fncall_inner(expr)?,
+                TokenType::LBrack => expr = self.arrindex_inner(expr)?,
+                _ => return Ok(expr)
+            }
         }
+        Ok(expr)
+    }
+
+    fn fncall_inner(&mut self, expr: Expr) -> Result<Expr, ParserError> {
+        let lparen = self.next();
+        let args = self.commalist(TokenType::RParen, Self::assignment)?;
+        Ok(Expr::FuncCall { func: Box::new(expr), args, pos: lparen.pos.clone() })
+    }
+
+    fn arrindex_inner(&mut self, expr: Expr) -> Result<Expr, ParserError> {
+        let lbrack = self.next();
+        let index = self.assignment()?;
+        self.err_on_eof()?;
+        if self.next().ty != TokenType::RBrack {
+            return Err(ParserError { message: "Expected RBrack after collection index".into(), pos: lbrack.pos.clone() });
+        }
+        Ok(Expr::Index { lhs: Box::new(expr), index: Box::new(index), pos: lbrack.pos.clone() })
     }
 
     fn expr_base(&mut self) -> Result<Expr, ParserError> {
diff --git a/src/stdlib/mod.rs b/src/stdlib/mod.rs
index 6c4b3e8..882d904 100644
--- a/src/stdlib/mod.rs
+++ b/src/stdlib/mod.rs
@@ -14,6 +14,14 @@ pub fn load(env: &mut Environment) {
     env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_println, arg_count: 1, name }));
     name = Rc::from("input"); 
     env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_input, arg_count: 0, name }));
+    name = Rc::from("ord"); 
+    env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_ord, arg_count: 1, name }));
+    name = Rc::from("chr"); 
+    env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_chr, arg_count: 1, name }));
+    name = Rc::from("range"); 
+    env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_range, arg_count: 2, name }));
+    name = Rc::from("len"); 
+    env.declare(name.clone(), Value::BuiltinFn(BuiltinFn { func: fn_len, arg_count: 1, name }));
 }
 
 fn fn_str(args: Vec<Value>) -> Result<Value, String> {
@@ -39,5 +47,55 @@ fn fn_input(_: Vec<Value>) -> Result<Value, String> {
     let mut buffer = String::new();
     let stdin = std::io::stdin();
     stdin.read_line(&mut buffer).map_err(|e| e.to_string())?;
+    if buffer.ends_with("\n") {
+        buffer.pop();
+    }
     Ok(Value::from(buffer))
+}
+
+fn fn_ord(args: Vec<Value>) -> Result<Value, String> {
+    if let Value::Char(c) = args[0] {
+        Ok(Value::from(c as u32))
+    } else {
+        Err("Argument to ord must be a char".into())
+    }
+}
+
+fn fn_chr(args: Vec<Value>) -> Result<Value, String> {
+    if let Value::Int(i) = args[0] {
+        if i >= 0 && i < (u32::MAX as i64) {
+            if let Some(c) = char::from_u32(i as u32) {
+                return Ok(Value::from(c))
+            }
+        }
+        Err("Out of range".into())
+    } else {
+        Err("Argument to chr must be an integer".into())
+    }
+}
+
+fn fn_range(args: Vec<Value>) -> Result<Value, String> {
+    let min = &args[0];
+    let max = &args[1];
+    match (min, max) {
+        (Value::Int(a), Value::Int(b)) => {
+            if a == b {
+                Ok(Value::from(vec![]))
+            } else if a < b {
+                Ok(Value::from((*a..*b).map(|x| Value::Int(x)).collect::<Vec<Value>>()))
+            } else {
+                Ok(Value::from(((*b+1)..(*a+1)).rev().map(|x| Value::Int(x)).collect::<Vec<Value>>()))
+            }
+        },
+        _ => Err("Both arguments to range must be integers".into())
+    }
+}
+
+fn fn_len(args: Vec<Value>) -> Result<Value, String> {
+    match &args[0] {
+        Value::String(s) => Ok(Value::Int(s.len() as i64)),
+        Value::List(l) => Ok(Value::Int(l.borrow().len() as i64)),
+        Value::Map(m) => Ok(Value::Int(m.len() as i64)),
+        v => Err(format!("{:?} has no length", v))
+    }
 }
\ No newline at end of file
diff --git a/src/value.rs b/src/value.rs
index f68d48c..9a4a314 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -1,4 +1,4 @@
-use std::{rc::Rc, collections::HashMap, ops::*, fmt, cmp::Ordering};
+use std::{rc::Rc, collections::HashMap, ops::*, fmt, cmp::Ordering, cell::RefCell};
 
 use num_traits::{Zero, ToPrimitive};
 
@@ -41,7 +41,7 @@ pub enum Value {
     Bool(bool), 
     Char(char),
     String(Rc<str>), 
-    List(Rc<Vec<Value>>), Map(Rc<HashMap<Value,Value>>),
+    List(Rc<RefCell<Vec<Value>>>), Map(Rc<HashMap<Value,Value>>),
     BuiltinFn(BuiltinFn),
     Data(Data),
 }
@@ -55,7 +55,7 @@ impl Value {
             Complex(z) => !z.is_zero(),
             Rational(r) => !r.is_zero(),
             String(s) => !s.len() == 0,
-            List(l) => !l.len() == 0,
+            List(l) => !l.borrow().len() == 0,
             Map(m) => !m.len() == 0,
             _ => true
         }
@@ -66,7 +66,7 @@ impl Value {
             Value::String(s) 
                 => Ok(Box::new(s.chars()
                     .map(|c| Value::Char(c)))),
-            Value::List(l) => Ok(Box::new(l.iter().cloned())),
+            Value::List(l) => Ok(Box::new(l.borrow().clone().into_iter())),
             _ => Err(())
         }
     }
@@ -120,13 +120,51 @@ impl Value {
             Self::Complex(z) => Rc::from(z.to_string()),
             Self::Char(c) => Rc::from(format!("'{}'", c)), // TODO escaping
             Self::String(s) => Rc::from(format!("\"{}\"", s)), // TODO escaping
-            Self::List(l) => Rc::from(format!("{:?}", l)), // TODO fix
+            Self::List(l) => Rc::from(format!("{:?}", l.borrow())), // TODO fix
             Self::Map(m) => Rc::from(format!("{:?}", m)), // TODO fix
             Self::Type(_) => todo!(),
             Self::BuiltinFn(bf) => Rc::from(format!("<builtin fn {} at {:?}>", bf.name, bf.func as *const ())),
             Self::Data(_) => todo!(),
         }
     }
+
+    pub fn index(&self, idx: &Value) -> Result<Value, String> {
+        match self {
+            Self::String(s) => match idx {
+                Value::Int(i) if *i >= 0 => s.chars().nth(*i as usize)
+                    .ok_or_else(|| format!("String index {} out of bounds for length {}", i, s.chars().count()))
+                    .map(|c| Value::Char(c)),
+                Value::Int(i) => Err(format!("String index {} cannot be negative", i)),
+                _ => Err(format!("Cannot index {:?} with {:?}", self, idx))
+            },
+            Self::List(l) => match idx {
+                Value::Int(i) if *i >= 0 => l.borrow().get(*i as usize)
+                    .ok_or_else(|| format!("List index {} out of bounds for length {}", i, l.borrow().len()))
+                    .map(|v| v.clone()),
+                Value::Int(i) => Err(format!("List index {} cannot be negative", i)),
+                _ => Err(format!("Cannot index {:?} with {:?}", self, idx))
+            }
+            Self::Map(_) => todo!(),
+            v => Err(format!("Cannot index into {:?}", v))
+        }
+    }
+
+    pub fn assign_index(&self, idx: &Value, value: Value) -> Result<(), String> {
+        match self {
+            Self::String(s) => todo!("Can't mutate strings yet"),
+            Self::List(l) => match idx {
+                Value::Int(i) if *i >= 0 && (*i as usize) < l.borrow().len() => {
+                    l.borrow_mut()[*i as usize] = value;
+                    Ok(())
+                }
+                Value::Int(i) if *i >= 0 => Err(format!("List index {} out of bounds for length {}", i, l.borrow().len())),
+                Value::Int(i) => Err(format!("List index {} cannot be negative", i)),
+                _ => Err(format!("Cannot index {:?} with {:?}", self, idx))
+            }
+            Self::Map(_) => todo!(),
+            v => Err(format!("Cannot index into {:?}", v))
+        }
+    }
 }
 
 impl PartialEq for Value {
@@ -202,6 +240,23 @@ macro_rules! value_from {
     };
 }
 
+impl From<Vec<Value>> for Value {
+    fn from(x: Vec<Value>) -> Self {
+        Self::List(RefCell::new(x).into())
+    }
+}
+
+value_from!(Int, u8 u16 u32 i8 i16 i32 i64);
+value_from!(Float, f32 f64);
+value_from!(Complex, Complex);
+value_from!(Rational, Rational);
+value_from!(Bool, bool);
+value_from!(String, String Rc<str>);
+value_from!(List, RefCell<Vec<Value>>);
+value_from!(Char, char);
+value_from!(Map, HashMap<Value,Value>);
+
+
 macro_rules! impl_numeric_op {
     ($optrait:ty, $fnname:ident, { $($bonus:tt)* }) => {
         impl $optrait for &Value {
@@ -235,15 +290,15 @@ macro_rules! impl_numeric_op {
     }
 }
 
-value_from!(Int, u8 u16 u32 i8 i16 i32 i64);
-value_from!(Float, f32 f64);
-value_from!(Complex, Complex);
-value_from!(Rational, Rational);
-value_from!(Bool, bool);
-value_from!(String, String Rc<str>);
-value_from!(Char, char);
-value_from!(List, Vec<Value>);
-value_from!(Map, HashMap<Value,Value>);
+impl Neg for Value {
+    type Output = Result<Value, String>;
+    fn neg(self) -> Self::Output {
+        match self {
+            Value::Int(a) => Ok(Value::Int(-a)),
+            _ => Err(format!("Unsupported operation 'neg' on {:?}", self))
+        }
+    }
+}
 
 impl_numeric_op!(Add, add, {
     (String(a), String(b)) => Ok(((**a).to_owned() + b).into()),
@@ -260,11 +315,16 @@ impl_numeric_op!(Add, add, {
     }
     (List(a), List(b)) => {
         let mut a = (**a).clone();
-        a.append(&mut (**b).clone());
+        a.borrow_mut().append(&mut (**b).borrow().clone());
         Ok(a.into())
     },
 });
 impl_numeric_op!(Sub, sub, {});
-impl_numeric_op!(Mul, mul, {});
+impl_numeric_op!(Mul, mul, {
+    (String(a), Int(b)) | (Int(b), String(a)) 
+        => Ok(Value::from(a.chars().cycle().take(a.chars().count()*(*b as usize)).collect::<std::string::String>())),
+    (List(a), Int(b)) | (Int(b), List(a))
+        => Ok(Value::from(a.borrow().iter().cycle().take(a.borrow().len()*(*b as usize)).cloned().collect::<Vec<Value>>())),
+});
 impl_numeric_op!(Div, div, {});
 impl_numeric_op!(Rem, rem, {});
\ No newline at end of file