diff --git a/assets/prelude.ld b/assets/prelude.ld
index 7d2646b..6c9ed8e 100644
--- a/assets/prelude.ld
+++ b/assets/prelude.ld
@@ -295,7 +295,13 @@ fn concat {
 fn contains? {
 	"Returns true if a set or list contains a value."
 	& (value, s as :set) -> bool (base :get	(s, value))
-	(value, l as :list) -> contains? (value, set (list))
+	(value, l as :list) -> loop (l) with {
+		([]) -> false
+		([x]) -> eq? (x, value)
+		([x, ...xs]) -> if eq? (x, value)
+			then true
+			else recur (xs)
+	}
 }
 
 & fn omit {
diff --git a/assets/test_prelude.ld b/assets/test_prelude.ld
index 6734057..195b361 100644
--- a/assets/test_prelude.ld
+++ b/assets/test_prelude.ld
@@ -10,6 +10,8 @@ fn dec (n as :number) -> base :sub (n, 1)
 
 fn sub (x as :number, y as :number) -> base :sub (x, y)
 
+fn panics! () -> add ("foo", "bar")
+
 fn print!(x) -> base :print! (x)
 
-#{add, dec, sub, print!}
+#{add, dec, sub, print!, panics!}
diff --git a/src/base.rs b/src/base.rs
index edee9a7..3c4d8ce 100644
--- a/src/base.rs
+++ b/src/base.rs
@@ -257,7 +257,9 @@ pub fn or<'src>(x: &Value<'src>, y: &Value<'src>) -> Value<'src> {
     Value::Boolean(x.bool() || y.bool())
 }
 
+// TODO: fix this: x is a list of all the args passed to Ludus's print!
 pub fn print<'src>(x: &Value<'src>) -> Value<'src> {
+    // dbg!(x)
     println!("{}", x);
     Value::Keyword("ok")
 }
diff --git a/src/main.rs b/src/main.rs
index adbe1a8..ca9c620 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,7 +15,7 @@
 // * [x] investigate using labels (which is behind a compiler flag, somehow)
 // * [ ] write parsing errors
 // * [ ] wire up Ariadne parsing errors
-// * [ ] add stack traces and code locations to panics
+// * [x] add stack traces and code locations to panics
 // * [x] validation
 // * [x] break this out into multiple files
 // * [x] write a tree-walk VM
@@ -70,7 +70,7 @@ pub fn prelude<'src>() -> (
     Vec<(String, Value<'src>)>,
     std::collections::HashMap<*const Ast, FnInfo>,
 ) {
-    let prelude = Asset::get("test_prelude.ld").unwrap().data.into_owned();
+    let prelude = Asset::get("prelude.ld").unwrap().data.into_owned();
     // we know for sure Prelude should live through the whole run of the program
     let leaked = Box::leak(Box::new(prelude));
     let prelude = std::str::from_utf8(leaked).unwrap();
diff --git a/src/validator.rs b/src/validator.rs
index 6fad284..4ff9ade 100644
--- a/src/validator.rs
+++ b/src/validator.rs
@@ -536,7 +536,7 @@ impl<'a, 'src: 'a> Validator<'a, 'src> {
                     unreachable!()
                 };
 
-                dbg!(&input);
+                // dbg!(&input);
 
                 let tailpos = self.status.tail_position;
                 self.status.tail_position = true;
@@ -551,7 +551,7 @@ impl<'a, 'src: 'a> Validator<'a, 'src> {
                     self.ast = expr;
                     self.span = *span;
                     let arity = self.arity();
-                    dbg!(&arity);
+                    // dbg!(&arity);
                     match arity {
                         Arity::Fixed(clause_arity) => {
                             if clause_arity != loop_arity {
@@ -644,7 +644,7 @@ impl<'a, 'src: 'a> Validator<'a, 'src> {
                     },
                     _ => {
                         println!("internal Ludus error: unexpected splat pattern");
-                        dbg!(splatted);
+                        // dbg!(splatted);
                         unreachable!()
                     }
                 }