simple expression

schala-lang/language/src/visitor.rs

@@ -1,4 +1,13 @@
+use crate::ast::ExpressionKind;
 
-pub trait ASTVisitor {
-
+pub trait ExpressionKindVisitor<T> {
+  fn nat_literal(&mut self, n: u64) -> T;
+}
+
+pub fn dispatch<T>(input: &mut ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
+  use ExpressionKind::*;
+  match input {
+    NatLiteral(n) => visitor.nat_literal(*n),
+    _ => panic!()
+  }
 }