diff --git a/Cargo.lock b/Cargo.lock
index f9d798a..293058c 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -445,9 +445,9 @@ checksum = "3c5e1a9a646d36c3599cd173a41282daf47c44583ad367b8e6837255952e5c67"
 
 [[package]]
 name = "syn"
-version = "2.0.90"
+version = "2.0.91"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "919d3b74a5dd0ccd15aeb8f93e7006bd9e14c295087c9896a110f490752bcf31"
+checksum = "d53cbcb5a243bd33b7858b1d7f4aca2153490815872d86d955d6ea29f743c035"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/talc-bin/Cargo.toml b/talc-bin/Cargo.toml
index bfcbcae..6a70332 100644
--- a/talc-bin/Cargo.toml
+++ b/talc-bin/Cargo.toml
@@ -2,6 +2,7 @@
 name = "talc-bin"
 version = "0.2.2"
 edition = "2021"
+rust-version = "1.81.0"
 
 [[bin]]
 name = "talc"
diff --git a/talc-lang/Cargo.toml b/talc-lang/Cargo.toml
index cbeb161..692d47c 100644
--- a/talc-lang/Cargo.toml
+++ b/talc-lang/Cargo.toml
@@ -2,6 +2,7 @@
 name = "talc-lang"
 version = "0.2.2"
 edition = "2021"
+rust-version = "1.81.0"
 
 [dependencies]
 num = { version = "0.4", features = [] }
diff --git a/talc-lang/src/compiler.rs b/talc-lang/src/compiler.rs
index 10f81ce..7399882 100644
--- a/talc-lang/src/compiler.rs
+++ b/talc-lang/src/compiler.rs
@@ -69,6 +69,7 @@ struct Compiler<'a> {
 	attrs: FuncAttrs,
 	// variables
 	scope: HashMap<Symbol, VarKind>,
+	scope_count: usize,
 	shadowed: Vec<(Symbol, Option<VarKind>)>,
 	closes: Vec<(Symbol, usize)>,
 	local_count: usize,
@@ -85,7 +86,16 @@ pub fn compile(expr: &Expr, name: Option<Symbol>) -> Result<Function> {
 
 pub fn compile_repl(expr: &Expr, globals: &mut Vec<Symbol>) -> Result<Function> {
 	let mut comp = Compiler::new_repl(globals);
-	comp.expr(expr)?;
+	match &expr.kind {
+		ExprKind::Block(xs) => {
+			for x in &xs[0..xs.len() - 1] {
+				comp.expr(x)?;
+				comp.emit_discard();
+			}
+			comp.expr(&xs[xs.len() - 1])?;
+		}
+		_ => comp.expr(expr)?,
+	}
 	Ok(comp.finish_repl(globals))
 }
 
@@ -99,6 +109,7 @@ impl<'a> Default for Compiler<'a> {
 			chunk: Chunk::new(),
 			attrs: FuncAttrs::default(),
 			scope,
+			scope_count: 0,
 			shadowed: Vec::new(),
 			local_count: 1,
 			closes: Vec::new(),
@@ -286,10 +297,12 @@ impl<'a> Compiler<'a> {
 
 	#[must_use]
 	fn begin_scope(&mut self) -> usize {
+		self.scope_count += 1;
 		self.shadowed.len()
 	}
 
 	fn end_scope(&mut self, scope: usize) {
+		self.scope_count -= 1;
 		let mut locals = 0;
 		while self.shadowed.len() > scope {
 			let (name, var) = self.shadowed.pop().expect("scope bad");
@@ -377,6 +390,9 @@ impl<'a> Compiler<'a> {
 	}
 
 	fn declare_global(&mut self, name: Symbol) {
+		if self.scope.get(&name) == Some(&VarKind::Global) {
+			return
+		}
 		let shadowed = self.scope.insert(name, VarKind::Global);
 		self.shadowed.push((name, shadowed));
 	}
@@ -403,7 +419,10 @@ impl<'a> Compiler<'a> {
 			ResolveOutcome::Var(VarKind::Global) => {
 				self.emit(I::StoreGlobal(Arg24::from_symbol(name)));
 			}
-			ResolveOutcome::None if self.mode == CompilerMode::Repl => {
+			ResolveOutcome::None
+				if self.mode == CompilerMode::Repl && self.scope_count == 0 =>
+			{
+				self.declare_global(name);
 				self.emit(I::StoreGlobal(Arg24::from_symbol(name)));
 			}
 			ResolveOutcome::None => {
diff --git a/talc-lang/src/exception.rs b/talc-lang/src/exception.rs
index febebb5..2ef63a9 100644
--- a/talc-lang/src/exception.rs
+++ b/talc-lang/src/exception.rs
@@ -10,31 +10,23 @@ pub type Result<T> = std::result::Result<T, Exception>;
 #[derive(Clone, Debug)]
 pub struct Exception {
 	pub ty: Symbol,
-	pub msg: Option<Rc<LStr>>,
+	pub msg: Rc<LStr>,
 }
 
 impl Exception {
-	pub fn new(ty: Symbol) -> Self {
-		Self { ty, msg: None }
-	}
-
-	pub fn new_with_msg(ty: Symbol, msg: Rc<LStr>) -> Self {
-		Self { ty, msg: Some(msg) }
+	pub fn new(ty: Symbol, msg: Rc<LStr>) -> Self {
+		Self { ty, msg }
 	}
 
 	pub fn from_table(table: &Rc<RefCell<HashMap<HashValue, Value>>>) -> Option<Self> {
 		let table = table.borrow();
 		let ty = table.get(&(*SYM_TYPE).into())?;
-		if let Value::Symbol(ty) = ty {
-			let msg = table.get(&(*SYM_MSG).into());
-			match msg {
-				None => Some(Self { ty: *ty, msg: None }),
-				Some(Value::String(msg)) => Some(Self {
-					ty: *ty,
-					msg: Some(msg.clone()),
-				}),
-				Some(_) => None,
-			}
+		let msg = table.get(&(*SYM_MSG).into())?;
+		if let (Value::Symbol(ty), Value::String(msg)) = (ty, msg) {
+			Some(Self {
+				ty: *ty,
+				msg: msg.clone(),
+			})
 		} else {
 			None
 		}
@@ -43,27 +35,21 @@ impl Exception {
 	pub fn to_table(self) -> Rc<RefCell<HashMap<HashValue, Value>>> {
 		let mut table = HashMap::new();
 		table.insert((*SYM_TYPE).into(), self.ty.into());
-		if let Some(msg) = self.msg {
-			table.insert((*SYM_MSG).into(), Value::String(msg));
-		}
+		table.insert((*SYM_MSG).into(), Value::String(self.msg));
 		Rc::new(RefCell::new(table))
 	}
 }
 
 impl Display for Exception {
 	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-		if let Some(msg) = &self.msg {
-			write!(f, "{}: {}", self.ty.name(), msg)
-		} else {
-			write!(f, "{}", self.ty.name())
-		}
+		write!(f, "{}: {}", self.ty.name(), self.msg)
 	}
 }
 
 #[macro_export]
 macro_rules! exception {
 	($exc_ty:expr, $($t:tt)*) => {
-		$crate::exception::Exception::new_with_msg(
+		$crate::exception::Exception::new(
 			$exc_ty,
 			$crate::lstring::LString::from(
 				format!($($t)*)
@@ -73,9 +59,6 @@ macro_rules! exception {
 	($exc_ty:expr, $fstr:literal) => {
 		$crate::exception::exception!($exc_ty, $fstr,)
 	};
-	($exc_ty:expr) => {
-		$crate::exception::Exception::new($exc_ty)
-	};
 }
 
 pub use exception;
diff --git a/talc-lang/src/parser/parser.rs b/talc-lang/src/parser/parser.rs
index 9068795..d6a8164 100644
--- a/talc-lang/src/parser/parser.rs
+++ b/talc-lang/src/parser/parser.rs
@@ -205,6 +205,18 @@ impl<'s> Parser<'s> {
 		self.lexer.peek().unwrap().clone()
 	}
 
+	fn parse_symbol(tok: Token) -> Result<Symbol> {
+		let inner = &tok.content[1..];
+		let s = match inner.chars().next() {
+			Some('\'') => Symbol::get(&inner[1..inner.len() - 1]),
+			Some('\"') => Symbol::get(
+				&parse_str_escapes(&inner[1..inner.len() - 1]).span_err(tok.span)?,
+			),
+			_ => Symbol::get(inner),
+		};
+		Ok(s)
+	}
+
 	fn parse_table_items(&mut self) -> Result<Vec<TableItem>> {
 		let mut items = Vec::new();
 		loop {
@@ -284,7 +296,7 @@ impl<'s> Parser<'s> {
 	fn parse_symbol_list(&mut self) -> Result<Vec<Symbol>> {
 		let mut syms = Vec::new();
 		while let Some(tok) = try_next!(self, T::Symbol) {
-			syms.push(Symbol::get(tok.content));
+			syms.push(Self::parse_symbol(tok)?);
 			if try_next!(self, T::Comma).is_none() {
 				break
 			}
@@ -420,16 +432,8 @@ impl<'s> Parser<'s> {
 				Ok(E::Literal(s.into()).span(tok.span))
 			}
 			T::Symbol => {
-				let inner = &tok.content[1..];
-				let s = match inner.chars().next() {
-					Some('\'') => Symbol::get(&inner[1..inner.len() - 1]),
-					Some('\"') => Symbol::get(
-						&parse_str_escapes(&inner[1..inner.len() - 1])
-							.span_err(tok.span)?,
-					),
-					_ => Symbol::get(inner),
-				};
-				Ok(E::Literal(s.into()).span(tok.span))
+				let s = Self::parse_symbol(tok)?;
+				Ok(E::Literal(Value::from(s)).span(tok.span))
 			}
 			T::True => Ok(E::Literal(Value::Bool(true)).span(tok.span)),
 			T::False => Ok(E::Literal(Value::Bool(false)).span(tok.span)),
@@ -531,6 +535,28 @@ impl<'s> Parser<'s> {
 		Ok(lhs)
 	}
 
+	fn parse_and(&mut self) -> Result<Expr> {
+		let mut lhs = self.parse_precedence(0)?;
+		let mut span = lhs.span;
+		while try_next!(self, T::And).is_some() {
+			let rhs = self.parse_precedence(0)?;
+			span += rhs.span;
+			lhs = E::And(b(lhs), b(rhs)).span(span);
+		}
+		Ok(lhs)
+	}
+
+	fn parse_or(&mut self) -> Result<Expr> {
+		let mut lhs = self.parse_and()?;
+		let mut span = lhs.span;
+		while try_next!(self, T::Or).is_some() {
+			let rhs = self.parse_and()?;
+			span += rhs.span;
+			lhs = E::Or(b(lhs), b(rhs)).span(span);
+		}
+		Ok(lhs)
+	}
+
 	fn parse_lambda(&mut self) -> Result<Expr> {
 		let tok = try_next!(self, T::Backslash | T::Amper);
 		match tok {
@@ -555,7 +581,7 @@ impl<'s> Parser<'s> {
 				let body_span = body.span;
 				Ok(E::Lambda(args, b(body)).span(span + body_span))
 			}
-			None => self.parse_precedence(0),
+			None => self.parse_or(),
 			_ => unreachable!("parse_lambda: guaranteed by try_next!"),
 		}
 	}
@@ -571,40 +597,8 @@ impl<'s> Parser<'s> {
 		Ok(lhs)
 	}
 
-	fn parse_not(&mut self) -> Result<Expr> {
-		if let Some(tok) = try_next!(self, T::Not) {
-			let expr = self.parse_not()?;
-			let span = tok.span + expr.span;
-			Ok(E::UnaryOp(UnaryOp::Not, b(expr)).span(span))
-		} else {
-			self.parse_pipeline()
-		}
-	}
-
-	fn parse_and(&mut self) -> Result<Expr> {
-		let mut lhs = self.parse_not()?;
-		let mut span = lhs.span;
-		while try_next!(self, T::And).is_some() {
-			let rhs = self.parse_not()?;
-			span += rhs.span;
-			lhs = E::And(b(lhs), b(rhs)).span(span);
-		}
-		Ok(lhs)
-	}
-
-	fn parse_or(&mut self) -> Result<Expr> {
-		let mut lhs = self.parse_and()?;
-		let mut span = lhs.span;
-		while try_next!(self, T::Or).is_some() {
-			let rhs = self.parse_and()?;
-			span += rhs.span;
-			lhs = E::Or(b(lhs), b(rhs)).span(span);
-		}
-		Ok(lhs)
-	}
-
 	fn parse_assign(&mut self) -> Result<Expr> {
-		let lhs = self.parse_or()?;
+		let lhs = self.parse_pipeline()?;
 		let lhs_span = lhs.span;
 		if let Some(op) = self.peek()?.kind.assign_op() {
 			let Some(lval) = LValue::from_expr(lhs) else {
diff --git a/talc-lang/src/value/index.rs b/talc-lang/src/value/index.rs
index 9d970e2..3e605d1 100644
--- a/talc-lang/src/value/index.rs
+++ b/talc-lang/src/value/index.rs
@@ -17,15 +17,19 @@ impl Value {
 		match (self, idx) {
 			(V::List(l), V::Int(i)) => {
 				let l = l.borrow();
-				let Some(i) = i.to_usize() else {
+				let Some(i) = i.to_isize() else {
 					throw!(
 						*SYM_INDEX_ERROR,
 						"index {i} out of bounds for list of length {}",
 						l.len()
 					)
 				};
-				if i < l.len() {
-					Ok(l[i].clone())
+				let mut j = i;
+				if j < 0 {
+					j += l.len() as isize;
+				}
+				if (0..l.len() as isize).contains(&j) {
+					Ok(l[j as usize].clone())
 				} else {
 					throw!(
 						*SYM_INDEX_ERROR,
@@ -84,15 +88,19 @@ impl Value {
 		match (self, idx) {
 			(V::List(l), V::Int(i)) => {
 				let mut l = l.borrow_mut();
-				let Some(i) = i.to_usize() else {
+				let Some(i) = i.to_isize() else {
 					throw!(
 						*SYM_INDEX_ERROR,
 						"index {i} out of bounds for list of length {}",
 						l.len()
 					)
 				};
-				if i < l.len() {
-					l[i] = val;
+				let mut j = i;
+				if j < 0 {
+					j += l.len() as isize;
+				}
+				if (0..l.len() as isize).contains(&j) {
+					l[j as usize] = val;
 					Ok(())
 				} else {
 					throw!(
diff --git a/talc-lang/src/value/ops.rs b/talc-lang/src/value/ops.rs
index 631ba48..606945c 100644
--- a/talc-lang/src/value/ops.rs
+++ b/talc-lang/src/value/ops.rs
@@ -28,15 +28,15 @@ impl Value {
 			Value::Bool(b) => *b,
 			Value::Range(r) => !r.is_empty(),
 			Value::Int(n) => !n.is_zero(),
-			Value::Float(x) => *x != 0.0 && !x.is_nan(),
+			Value::Float(x) => *x != 0.0,
 			Value::Ratio(r) => !r.is_zero(),
-			Value::Complex(c) => !(c.re == 0.0 && c.im == 0.0 || c.is_nan()),
+			Value::Complex(c) => !c.is_zero(),
 			Value::String(s) => !s.is_empty(),
-			Value::List(l) => l.borrow().len() > 0,
+			Value::List(l) => !l.borrow().is_empty(),
+			Value::Table(t) => !t.borrow().is_empty(),
 			Value::Cell(v) => v.borrow().truthy(),
 
 			Value::Symbol(_)
-			| Value::Table(_)
 			| Value::Function(_)
 			| Value::NativeFunc(_)
 			| Value::Native(_) => true,
diff --git a/talc-lang/src/vm.rs b/talc-lang/src/vm.rs
index dfc01c5..2a463af 100644
--- a/talc-lang/src/vm.rs
+++ b/talc-lang/src/vm.rs
@@ -258,7 +258,7 @@ impl Vm {
 			.interrupt
 			.fetch_and(false, std::sync::atomic::Ordering::Relaxed)
 		{
-			throw!(*SYM_INTERRUPTED)
+			throw!(*SYM_INTERRUPTED, "interrupted")
 		}
 		Ok(())
 	}
diff --git a/talc-macros/Cargo.toml b/talc-macros/Cargo.toml
index 7f65a69..6739e7c 100644
--- a/talc-macros/Cargo.toml
+++ b/talc-macros/Cargo.toml
@@ -2,6 +2,7 @@
 name = "talc-macros"
 version = "0.2.1"
 edition = "2021"
+rust-version = "1.68.2"
 
 [lib]
 proc-macro = true
diff --git a/talc-std/Cargo.toml b/talc-std/Cargo.toml
index 1bf1fa9..1ead113 100644
--- a/talc-std/Cargo.toml
+++ b/talc-std/Cargo.toml
@@ -2,6 +2,7 @@
 name = "talc-std"
 version = "0.2.2"
 edition = "2021"
+rust-version = "1.81.0"
 
 [dependencies]
 talc-lang = { path = "../talc-lang" }
diff --git a/talc-std/src/exception.rs b/talc-std/src/exception.rs
index a6e9bfd..644ccf8 100644
--- a/talc-std/src/exception.rs
+++ b/talc-std/src/exception.rs
@@ -8,27 +8,13 @@ use talc_macros::native_func;
 
 use crate::unpack_args;
 
-#[native_func(1)]
+#[native_func(2)]
 pub fn throw(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
-	let [_, arg] = unpack_args!(args);
-	let exc = match arg {
-		Value::Symbol(ty) => Exception::new(ty),
-		Value::List(l) => match l.borrow().as_slice() {
-			[Value::Symbol(ty)] | [Value::Symbol(ty), Value::Nil] => Exception::new(*ty),
-			[Value::Symbol(ty), Value::String(s)] => {
-				Exception::new_with_msg(*ty, s.clone())
-			}
-			[] | [_] | [_, _] => {
-				throw!(*SYM_TYPE_ERROR, "wrong argument for throw")
-			}
-			[_, _, _, ..] => throw!(
-				*SYM_VALUE_ERROR,
-				"too many elements in list argument for throw"
-			),
-		},
-		_ => throw!(*SYM_TYPE_ERROR, "throw expected symbol or list"),
+	let [_, ty, msg] = unpack_args!(args);
+	let (Value::Symbol(ty), Value::String(msg)) = (ty, msg) else {
+		throw!(*SYM_TYPE_ERROR, "throw expected symbol and string")
 	};
-	Err(exc)
+	Err(Exception::new(ty, msg))
 }
 
 #[native_func(1)]
@@ -38,9 +24,9 @@ pub fn rethrow(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
 		if let Some(e) = Exception::from_table(&table) {
 			return Err(e)
 		}
-		throw!(*SYM_VALUE_ERROR, "argument not a valid exception")
+		throw!(*SYM_VALUE_ERROR, "rethrow: argument not a valid exception")
 	}
-	throw!(*SYM_TYPE_ERROR, "argument not a valid exception")
+	throw!(*SYM_TYPE_ERROR, "rethrow expected table")
 }
 
 pub fn load(vm: &mut Vm) {
diff --git a/talc-std/src/math.rs b/talc-std/src/math.rs
index ec7039b..2c508d2 100644
--- a/talc-std/src/math.rs
+++ b/talc-std/src/math.rs
@@ -91,6 +91,7 @@ pub fn load(vm: &mut Vm) {
 	vm.set_global_name("arg", arg().into());
 	vm.set_global_name("abs", abs().into());
 	vm.set_global_name("abs_sq", abs_sq().into());
+	vm.set_global_name("conj", conj().into());
 
 	vm.set_global_name("sqrt", sqrt().into());
 	vm.set_global_name("cbrt", cbrt().into());
@@ -516,6 +517,18 @@ pub fn abs_sq(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
 	}
 }
 
+#[native_func(1)]
+pub fn conj(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
+	let [_, x] = unpack_args!(args);
+	match x {
+		Value::Int(_) => Ok(x),
+		Value::Ratio(_) => Ok(x),
+		Value::Float(_) => Ok(x),
+		Value::Complex(x) => Ok(Value::Complex(x.conj())),
+		x => throw!(*SYM_TYPE_ERROR, "conj expected numeric argument, got {x:#}"),
+	}
+}
+
 //
 //  continuous operations
 //