diff --git a/src/interpreter/value/function.rs b/src/interpreter/value/function.rs
index f3a0e28..d5c2435 100644
--- a/src/interpreter/value/function.rs
+++ b/src/interpreter/value/function.rs
@@ -1,2 +1,8 @@
+use super::Str;
+use crate::syntax::ast::{Expr, Spanned};
+
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct Function;
+pub struct Function<'s> {
+    params: Box<[Str<'s>]>,
+    ast: Box<[Spanned<Expr<'s>>]>,
+}
diff --git a/src/interpreter/value/mod.rs b/src/interpreter/value/mod.rs
index 51d5267..83b726f 100644
--- a/src/interpreter/value/mod.rs
+++ b/src/interpreter/value/mod.rs
@@ -23,8 +23,9 @@ pub enum Value<'s> {
     Keyword(Str<'s>),
     Number(OrderedF64),
     String(Str<'s>),
-    Function(Function),
-    Macro(Function),
+    Function(Function<'s>),
+    NativeFun(fn(&'s [Value<'s>]) -> Value<'s>),
+    Macro(Function<'s>),
 }
 
 impl<'s> From<Spanned<Expr<'s>>> for Value<'s> {
@@ -65,6 +66,7 @@ impl<'s> Display for Value<'s> {
             Value::Number(n) => n.fmt(f),
             Value::String(s) => write!(f, "\"{s}\""),
             Value::Function(_) => "#fun#".fmt(f),
+            Value::NativeFun(fp) => write!(f, "#native-fun({fp:p})#"),
             Value::Macro(_) => "#macro#".fmt(f),
         }
     }
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index e61d08f..5705a41 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -31,6 +31,8 @@ impl<T: PartialEq> PartialEq for Spanned<T> {
     }
 }
 
+impl<T: Eq> Eq for Spanned<T> {}
+
 impl<T: Hash> Hash for Spanned<T> {
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
         self.item.hash(state);
@@ -38,7 +40,7 @@ impl<T: Hash> Hash for Spanned<T> {
 }
 
 /// A Wisp AST
-#[derive(Debug, Clone, Hash, PartialEq)]
+#[derive(Debug, Clone, Hash, PartialEq, Eq)]
 pub enum Expr<'s> {
     List(Vec<Spanned<Self>>),
     Vector(Vec<Spanned<Self>>),