Add in better error reporting.

src/parser/sexp.rs

@@ -36,14 +36,14 @@ impl<'s> Token<'s> {
     pub fn as_list<'p>(&'p self) -> Result<&'p Vec<Token<'s>>, Box<dyn std::error::Error>> {
         Ok(match self {
             Token::List(children) => Ok(children),
-            _ => Err("wrong token type"),
+            _ => Err(format!("wrong token type {:?}", self)),
         }?)
     }
 
     pub fn as_atom<'p>(&'p self) -> Result<&'s str, Box<dyn std::error::Error>> {
         Ok(match self {
             Token::Atom(body) => Ok(*body),
-            _ => Err("wrong token type"),
+            _ => Err(format!("wrong token type {:?}", self)),
         }?)
     }