Fix the parser, make the function name optional.

src/syntax/ast.rs

@@ -27,7 +27,7 @@ pub struct Program {
 #[derive(Clone, Debug, PartialEq)]
 pub enum TopLevel {
     Statement(Statement),
-    Function(Name, Vec<Name>, Expression),
+    Function(Option<Name>, Vec<Name>, Expression),
 }
 
 /// A Name.