diff --git a/Cargo.lock b/Cargo.lock
index a72479b..2dcd065 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -445,9 +445,9 @@ checksum = "3c5e1a9a646d36c3599cd173a41282daf47c44583ad367b8e6837255952e5c67"
 
 [[package]]
 name = "syn"
-version = "2.0.93"
+version = "2.0.94"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c786062daee0d6db1132800e623df74274a0a87322d8e183338e01b3d98d058"
+checksum = "987bc0be1cdea8b10216bd06e2ca407d40b9543468fafd3ddfb02f36e77f71f3"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/docs/src/install/repl.md b/docs/src/install/repl.md
index 2abbd98..b445214 100644
--- a/docs/src/install/repl.md
+++ b/docs/src/install/repl.md
@@ -27,6 +27,17 @@ Use the up and down arrows to cycle through previous entries. By specifiying
 a history file with the `-H`/`--histfile` argument, history can be preserved
 between sessions.
 
+## Output formatting
+
+The `_fmt` global variable can be used to control output formatting. `_fmt` is
+a table where each key is a type and the corresponding value is the format
+string used to display that type. For example, setting `_fmt.int = "0x{:X}"`
+will cause the REPL to print integers in hexadecimal with a `0x` prefix.
+
+Values may also be `false` to disable printing entirely. Any other value will
+print using the default format. Initially, the value of `_fmt` is
+`{ :nil=false }`.
+
 ## Advanced features
 
 Use the `-a`/`--show-ast` flag to print the AST generated from the expression.
@@ -34,3 +45,4 @@ Use the `-d`/`--disasm` flag to show the disassembled bytecode generated by the
 compiler.
 The `--no-opt` flag disables the optimization step, which may affect the
 bytecode but should not affect behavior.
+
diff --git a/docs/src/lang/arithmetic.md b/docs/src/lang/arithmetic.md
index 58e7058..7c7fce1 100644
--- a/docs/src/lang/arithmetic.md
+++ b/docs/src/lang/arithmetic.md
@@ -93,6 +93,7 @@ false
 true
 >> 1 + 3i < 5
 Error: type_error: cannot compare 1.0+3.0i and 5
+    in <repl> at 4
 ```
 
 The boolean operators `and`, `or`, and `not` perform the expected operations
diff --git a/docs/src/lang/exceptions.md b/docs/src/lang/exceptions.md
index 1652237..d762f77 100644
--- a/docs/src/lang/exceptions.md
+++ b/docs/src/lang/exceptions.md
@@ -11,6 +11,7 @@ message (which must be a string).
 ```talc
 >> throw(:my_exception, "something bad happened!")
 Error: my_exception: something bad happened!
+    in <repl> at 1
 ```
 
 The exception can then be caught in a try-catch block:
diff --git a/docs/src/lang/variables.md b/docs/src/lang/variables.md
index fe16758..368df1c 100644
--- a/docs/src/lang/variables.md
+++ b/docs/src/lang/variables.md
@@ -57,6 +57,7 @@ you to write multiline programs.
 45
 >> y
 Error: name_error: undefined global y
+    in <repl> at 4
 ```
 
 Later we will see other expressions that create scopes, so it is important to
diff --git a/talc-bin/src/repl.rs b/talc-bin/src/repl.rs
index 0a448e7..4235027 100644
--- a/talc-bin/src/repl.rs
+++ b/talc-bin/src/repl.rs
@@ -1,4 +1,9 @@
-use std::{cell::RefCell, io::IsTerminal, process::ExitCode, rc::Rc};
+use std::{
+	cell::RefCell,
+	io::{stdout, IsTerminal, Write},
+	process::ExitCode,
+	rc::Rc,
+};
 
 use clap::ColorChoice;
 use rustyline::{
@@ -22,6 +27,7 @@ lazy_static::lazy_static! {
 	pub static ref SYM_PREV1: Symbol = symbol!("_");
 	pub static ref SYM_PREV2: Symbol = symbol!("__");
 	pub static ref SYM_PREV3: Symbol = symbol!("___");
+	pub static ref SYM__FMT: Symbol = symbol!("_fmt");
 }
 
 #[derive(Clone, Copy, Default)]
@@ -98,6 +104,32 @@ fn read_init_file(args: &Args) -> Result<Option<String>, std::io::Error> {
 	std::fs::read_to_string(file.to_os_str()).map(Some)
 }
 
+fn print_result(vm: &Vm, result: Value, c: &ReplColors) {
+	let ty = result.get_type();
+	let Some(Value::Table(g_fmt)) = vm.get_global(*SYM__FMT) else {
+		println!("{result:#}");
+		return
+	};
+	let g_fmt_ref = g_fmt.borrow();
+	let fmt = g_fmt_ref.get(&ty.into()).unwrap_or(&Value::Nil);
+	match fmt {
+		Value::String(fstr) => {
+			let res = talc_std::format::fmt_inner(fstr, &[result]);
+			match res {
+				Ok(s) => {
+					stdout().write_all(s.as_bytes()).expect("output failed");
+					stdout().write_all(b"\n").expect("output failed");
+				}
+				Err(e) => {
+					eprintln!("{}Error(fmt):{} {e}", c.error, c.reset);
+				}
+			}
+		}
+		Value::Bool(false) => (),
+		_ => println!("{result:#}"),
+	}
+}
+
 fn exec_line(
 	vm: &mut Vm,
 	line: &str,
@@ -144,9 +176,7 @@ fn exec_line(
 			let prev1 = vm.get_global(*SYM_PREV1).unwrap().clone();
 			vm.set_global(*SYM_PREV2, prev1);
 			vm.set_global(*SYM_PREV1, v.clone());
-			if v != Value::Nil {
-				println!("{v:#}");
-			}
+			print_result(vm, v, c);
 		}
 		Err(e) => eprintln!("{}Error:{} {e}", c.error, c.reset),
 	}
@@ -178,6 +208,12 @@ pub fn repl(args: &Args) -> ExitCode {
 	vm.set_global(*SYM_PREV1, Value::Nil);
 	vm.set_global(*SYM_PREV2, Value::Nil);
 	vm.set_global(*SYM_PREV3, Value::Nil);
+	vm.set_global(
+		*SYM__FMT,
+		Value::new_table(|table| {
+			table.insert(symbol!(nil).into(), Value::Bool(false));
+		}),
+	);
 
 	let init_src = match read_init_file(args) {
 		Ok(s) => s,
diff --git a/talc-lang/src/parser/lexer.rs b/talc-lang/src/parser/lexer.rs
index 571586c..a7a791e 100644
--- a/talc-lang/src/parser/lexer.rs
+++ b/talc-lang/src/parser/lexer.rs
@@ -6,6 +6,32 @@ use super::{ParserError, Pos, Span};
 
 type Result<T> = std::result::Result<T, ParserError>;
 
+pub static KEYWORDS: &[&[u8]] = &[
+	b"and",
+	b"break",
+	b"catch",
+	b"continue",
+	b"do",
+	b"elif",
+	b"else",
+	b"end",
+	b"false",
+	b"fn",
+	b"for",
+	b"global",
+	b"if",
+	b"in",
+	b"nil",
+	b"not",
+	b"or",
+	b"return",
+	b"then",
+	b"true",
+	b"try",
+	b"var",
+	b"while",
+];
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum TokenKind {
 	Eof,
diff --git a/talc-lang/src/value/mod.rs b/talc-lang/src/value/mod.rs
index 3849040..fc3f1c8 100644
--- a/talc-lang/src/value/mod.rs
+++ b/talc-lang/src/value/mod.rs
@@ -8,6 +8,7 @@ use num::{complex::Complex64, BigInt};
 use crate::exception::{throw, Exception};
 use crate::lstring::{LStr, LString};
 use crate::number::{Int, Range, Ratio};
+use crate::parser::KEYWORDS;
 use crate::prelude::*;
 use crate::symbol::{Symbol, SYM_HASH_ERROR};
 
@@ -254,7 +255,7 @@ impl Value {
 			}
 			Self::Symbol(s) => {
 				let name = s.name();
-				if name.is_identifier() {
+				if name.is_identifier() && !KEYWORDS.contains(&name.as_bytes()) {
 					w.push_lstr(name);
 					Ok(())
 				} else {
diff --git a/talc-std/src/format.rs b/talc-std/src/format.rs
index f91c1d3..077adfc 100644
--- a/talc-std/src/format.rs
+++ b/talc-std/src/format.rs
@@ -438,15 +438,7 @@ fn format_arg(
 	Ok(())
 }
 
-#[native_func(2, "fmt")]
-pub fn fmt_(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
-	let [_, fstr, fargs] = unpack_args!(args);
-	let (Value::String(fstr), Value::List(fargs)) = (&fstr, &fargs) else {
-		throw!(
-			*SYM_TYPE_ERROR,
-			"format expected string and list, got {fstr:#} and {fargs:#}"
-		)
-	};
+pub fn fmt_inner(fstr: &LStr, fargs: &[Value]) -> Result<LString> {
 	let mut res = LString::new();
 	let mut faidx = 0;
 	let mut i = 0;
@@ -493,8 +485,21 @@ pub fn fmt_(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
 		}
 		let code = &fstr[start..i];
 		i += 1;
-		format_arg(&fargs.borrow(), &mut faidx, code, &mut res)?;
+		format_arg(fargs, &mut faidx, code, &mut res)?;
 	}
+	Ok(res)
+}
+
+#[native_func(2, "fmt")]
+pub fn fmt_(_: &mut Vm, args: Vec<Value>) -> Result<Value> {
+	let [_, fstr, fargs] = unpack_args!(args);
+	let (Value::String(fstr), Value::List(fargs)) = (&fstr, &fargs) else {
+		throw!(
+			*SYM_TYPE_ERROR,
+			"format expected string and list, got {fstr:#} and {fargs:#}"
+		)
+	};
+	let res = fmt_inner(fstr, &fargs.borrow())?;
 	Ok(res.into())
 }