diff --git a/src/eval.rs b/src/eval.rs
index 9748344..c9d1376 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -150,8 +150,10 @@ pub fn eval_expr(expr: &Expr, env: EnvRef) -> Result<Value, RuntimeError> {
         Expr::Binary { lhs, rhs, op } => match op.ty.get_op_type() {
             Some(OpType::Assignment) 
                 => eval_assignment(lhs, rhs, op, env),
-            Some(OpType::Additive) | Some(OpType::Multiplicative) 
+            Some(OpType::Additive) | Some(OpType::Multiplicative)
                 => eval_binary(lhs, rhs, op, env),
+            Some(OpType::Boolean) 
+                => eval_boolean(lhs, rhs, op, env),
             Some(OpType::Comparison)
                 => eval_comp(lhs, rhs, op, env),
             o => todo!("{:?}", o) // TODO other operations
@@ -178,7 +180,6 @@ pub fn eval_expr(expr: &Expr, env: EnvRef) -> Result<Value, RuntimeError> {
             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
     }
 }
 
@@ -275,6 +276,23 @@ pub fn eval_binary(lhs: &Box<Expr>, rhs: &Box<Expr>, op: &Token, env: EnvRef) ->
     }.map_err(|e| RuntimeError { message: e, pos: op.pos.clone() })
 }
 
+pub fn eval_boolean(lhs: &Box<Expr>, rhs: &Box<Expr>, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
+    let l = eval_expr(lhs, env.clone())?;
+    match op.ty {
+        TokenType::DoubleAmper => if l.truthy() {
+            eval_expr(rhs, env)
+        } else { 
+            Ok(l)
+        },
+        TokenType::DoublePipe => if !l.truthy() {
+            eval_expr(rhs, env)
+        } else { 
+            Ok(l)
+        },
+        _ => unreachable!()
+    }
+}
+
 pub fn eval_comp(lhs: &Box<Expr>, rhs: &Box<Expr>, op: &Token, env: EnvRef) -> Result<Value, RuntimeError> {
     let l = eval_expr(lhs, env.clone())?;
     let r = eval_expr(rhs, env)?;
@@ -308,6 +326,7 @@ pub fn eval_unary(arg: &Box<Expr>, op: &Token, env: EnvRef) -> Result<Value, Run
     let a = eval_expr(arg, env)?;
     match op.ty {
         TokenType::Minus => -a,
+        TokenType::Bang => Ok(Value::Bool(!a.truthy())),
         _ => todo!(),
     }.map_err(|e| RuntimeError { message: e, pos: op.pos.clone() })
 }
\ No newline at end of file
diff --git a/src/parser.rs b/src/parser.rs
index 83317b1..7ee246f 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -261,7 +261,11 @@ impl Parser {
     }
 
     fn pipeline(&mut self) -> Result<Expr, ParserError> {
-        self.expr(OpType::Pipeline, Self::comparison)
+        self.expr(OpType::Pipeline, Self::boolean)
+    }
+
+    fn boolean(&mut self) -> Result<Expr, ParserError> {
+        self.expr(OpType::Boolean, Self::comparison)
     }
 
     fn comparison(&mut self) -> Result<Expr, ParserError> {
diff --git a/src/token.rs b/src/token.rs
index 06414e4..86c4783 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -58,6 +58,8 @@ impl TokenType {
             | Self::StarEqual | Self::SlashEqual | Self::DoubleSlashEqual
             | Self::CaretEqual | Self::PercentEqual => Some(OpType::Assignment),
 
+            Self::DoubleAmper | Self::DoublePipe => Some(OpType::Boolean),
+
             _ => None
         }
     }
@@ -65,7 +67,7 @@ impl TokenType {
 
 #[derive(Clone,Copy,Debug,PartialEq)]
 pub enum OpType {
-    Assignment, Comparison, Pipeline, Additive, Multiplicative, Exponential
+    Assignment, Comparison, Pipeline, Additive, Multiplicative, Exponential, Boolean
 }
 
 impl OpType {
diff --git a/src/value.rs b/src/value.rs
index 9a4a314..0186294 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -151,7 +151,7 @@ impl Value {
 
     pub fn assign_index(&self, idx: &Value, value: Value) -> Result<(), String> {
         match self {
-            Self::String(s) => todo!("Can't mutate strings yet"),
+            Self::String(_) => 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;
@@ -314,7 +314,7 @@ impl_numeric_op!(Add, add, {
         Ok(s.into())
     }
     (List(a), List(b)) => {
-        let mut a = (**a).clone();
+        let a = (**a).clone();
         a.borrow_mut().append(&mut (**b).borrow().clone());
         Ok(a.into())
     },