1 files changed, 58 insertions, 1 deletions
diff --git a/lisp/src/ast.rs b/lisp/src/ast.rs
index 8cac963..929383f 100644
--- a/lisp/src/ast.rs
+++ b/lisp/src/ast.rs
@@ -1,7 +1,64 @@
-#[derive(Clone, Debug, PartialEq, Eq)]
+use std::fmt;
+
+#[derive(Clone, PartialEq, Eq)]
 pub enum Val {
     Atom(String),
     List(Vec<Self>),
     I64(i64),
     String(String),
 }
+
+impl fmt::Debug for Val {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Val::Atom(v) => write!(f, "{v}"),
+            Val::List(vs) => {
+                f.write_str("(")?;
+                for (i, v) in vs.iter().enumerate() {
+                    if i != 0 {
+                        f.write_str(" ")?;
+                    }
+                    v.fmt(f)?;
+                }
+                f.write_str(")")?;
+                Ok(())
+            }
+            Val::I64(v) => v.fmt(f),
+            Val::String(s) => s.fmt(f),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn print_string() {
+        assert_eq!(
+            format!("{:?}", Val::String("Hello, World!".to_string())),
+            "\"Hello, World!\"".to_string()
+        );
+    }
+    #[test]
+    fn print_atom() {
+        assert_eq!(
+            format!("{:?}", Val::Atom("boo-guff".to_string())),
+            "boo-guff".to_string()
+        );
+    }
+    #[test]
+    fn print_i64() {
+        assert_eq!(
+            format!("{:?}", Val::I64(1234)),
+            "1234".to_string()
+        );
+    }
+    #[test]
+    fn print_list() {
+        assert_eq!(
+            format!("{:?}", Val::List(vec!(Val::Atom("a".to_string()), Val::Atom("b".to_string())))),
+            "(a b)".to_string()
+        );
+    }
+}