diff --git a/src/main.rs b/src/main.rs
index dab6144..1bb9f81 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -43,7 +43,7 @@ mod vm;
 use crate::vm::*;
 
 pub fn main() {
-    let src = "let (x, 2) = (1, 2); x";
+    let src = "when { false -> :false, true -> :true}";
     let (tokens, lex_errs) = lexer().parse(src).into_output_errors();
     if lex_errs.len() > 0 {
         println!("{:?}", lex_errs);
diff --git a/src/parser.rs b/src/parser.rs
index 6c8f035..899b703 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -3,6 +3,12 @@ use crate::spans::*;
 use chumsky::{input::ValueInput, prelude::*, recursive::Recursive};
 use std::fmt;
 
+#[derive(Clone, Debug, PartialEq)]
+pub struct WhenClause<'src> {
+    pub cond: Spanned<Ast<'src>>,
+    pub body: Spanned<Ast<'src>>,
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub enum Ast<'src> {
     Error,
@@ -23,8 +29,7 @@ pub enum Ast<'src> {
     Let(Box<Spanned<Pattern<'src>>>, Box<Spanned<Self>>),
     Box(&'src str, Box<Spanned<Self>>),
     Synthetic(Box<Spanned<Self>>, Box<Spanned<Self>>, Vec<Spanned<Self>>),
-    WhenClause(Box<Spanned<Self>>, Box<Spanned<Self>>),
-    When(Vec<Spanned<Self>>),
+    When(Vec<Spanned<WhenClause<'src>>>),
     MatchClause(Box<Spanned<Pattern<'src>>>, Box<Spanned<Self>>),
     Match(Box<Spanned<Self>>, Vec<Spanned<Self>>),
     FnClause(Box<Spanned<Pattern<'src>>>, Box<Spanned<Self>>),
@@ -382,7 +387,7 @@ where
         .clone()
         .then_ignore(just(Token::Punctuation("->")))
         .then(expr.clone())
-        .map_with(|(cond, body), e| (Ast::WhenClause(Box::new(cond), Box::new(body)), e.span()));
+        .map_with(|(cond, body), e| (WhenClause { cond, body }, e.span()));
 
     let when = just(Token::Reserved("when"))
         .ignore_then(
diff --git a/src/value.rs b/src/value.rs
index 2deb170..539902c 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -1,6 +1,7 @@
 use crate::parser::*;
 use crate::spans::*;
 use imbl::*;
+use std::cell::RefCell;
 use std::fmt;
 use std::rc::Rc;
 
@@ -31,6 +32,7 @@ pub enum Value<'src> {
     List(Rc<Vector<Self>>),
     // ref-counted, immutable, persistent
     Dict(Rc<HashMap<&'src str, Self>>),
+    Box(&'src str, Box<Self>),
     // Fn(Rc<Fn<'src>>),
     // Set(HashSet<Self>),
     // Sets are hard
@@ -55,6 +57,7 @@ impl<'src> Clone for Value<'src> {
             Value::Tuple(t) => Value::Tuple(t.clone()),
             Value::List(l) => Value::List(l.clone()),
             Value::Dict(d) => Value::Dict(d.clone()),
+            Value::Box(name, b) => Value::Box(name, b.clone()),
         }
     }
 }
@@ -85,6 +88,7 @@ impl<'src> fmt::Display for Value<'src> {
                     .join(", ")
             ),
             Value::Dict(d) => write!(f, "#{{{:?}}}", d),
+            Value::Box(name, b) => write!(f, "box {} [ {} ]", name, b),
         }
     }
 }
diff --git a/src/vm.rs b/src/vm.rs
index d98705a..c5988ad 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -5,7 +5,7 @@ use std::rc::Rc;
 
 #[derive(Clone, Debug)]
 pub struct LudusError {
-    msg: &'static str,
+    msg: String,
 }
 
 // oy
@@ -156,7 +156,9 @@ pub fn eval<'src, 'a>(
             let val = eval(&expr.0, ctx)?;
             match matchh(&patt.0, &val, ctx) {
                 Some(_) => Ok(val),
-                None => Err(LudusError { msg: "No match" }),
+                None => Err(LudusError {
+                    msg: "No match".to_string(),
+                }),
             }
         }
         Ast::Placeholder => todo!(),
@@ -166,15 +168,45 @@ pub fn eval<'src, 'a>(
         Ast::Pair(_, _) => todo!(),
         Ast::Box(_, _) => todo!(),
         Ast::Synthetic(_, _, _) => todo!(),
-        Ast::When(_) => todo!(),
-        Ast::WhenClause(_, _) => todo!(),
+        Ast::When(clauses) => {
+            for clause in clauses.iter() {
+                let WhenClause { cond, body } = &clause.0;
+                if eval(&cond.0, ctx)?.bool() {
+                    return eval(&body.0, ctx);
+                };
+            }
+            return Err(LudusError {
+                msg: "no match".to_string(),
+            });
+        }
         Ast::Match(_, _) => todo!(),
         Ast::MatchClause(_, _) => todo!(),
         Ast::Fn(_, _) => todo!(),
         Ast::FnDeclaration(_) => todo!(),
         Ast::FnClause(_, _) => todo!(),
-        Ast::Panic(_) => todo!(),
-        Ast::Repeat(_, _) => todo!(),
+        Ast::Panic(msg) => {
+            let msg = eval(&msg.0, ctx)?;
+            Err(LudusError {
+                msg: msg.to_string(),
+            })
+        }
+        Ast::Repeat(times, body) => {
+            let mut times_num = 0;
+            match eval(&times.0, ctx) {
+                Ok(Value::Number(n)) => {
+                    times_num = n as usize;
+                }
+                _ => {
+                    return Err(LudusError {
+                        msg: "repeat may only take numbers".to_string(),
+                    })
+                }
+            }
+            for _ in 0..times_num {
+                let _ = eval(&body.0, ctx)?;
+            }
+            Ok(Value::Nil)
+        }
         Ast::Do(_) => todo!(),
         Ast::Loop(_, _) => todo!(),
         Ast::Recur(_) => todo!(),