Super-simple visitor doing something

schala-lang/language/src/visitor.rs

@@ -1,13 +1,48 @@
-use crate::ast::ExpressionKind;
+use std::rc::Rc;
+
+use crate::builtin::{BinOp, PrefixOp};
+use crate::ast::{Expression, ExpressionKind};
 
 pub trait ExpressionKindVisitor<T> {
-  fn nat_literal(&mut self, n: u64) -> T;
+  fn nat_literal(&mut self, n: &u64) -> T;
+  fn string_literal(&mut self, s: Rc<String>) -> T;
+  fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression) -> T;
 }
 
-pub fn dispatch<T>(input: &mut ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
+pub fn dispatch<T>(input: &ExpressionKind, visitor: &mut dyn ExpressionKindVisitor<T>) -> T {
   use ExpressionKind::*;
   match input {
-    NatLiteral(n) => visitor.nat_literal(*n),
+    NatLiteral(n) => visitor.nat_literal(n),
+    StringLiteral(s) => visitor.string_literal(s.clone()),
+    BinExp(op, box lhs, box rhs) => visitor.binexp(op, lhs.node(), rhs.node()),
     _ => panic!()
   }
 }
+
+struct NumberSummer;
+
+impl ExpressionKindVisitor<u64> for NumberSummer {
+  fn nat_literal(&mut self, n: &u64) -> u64 {
+    n.clone()
+  }
+  fn string_literal(&mut self, s: Rc<String>) -> u64 {
+    0
+  }
+  fn binexp(&mut self, op: &BinOp, lhs: &Expression, rhs: &Expression)  -> u64 {
+    let lhs = dispatch(&lhs.kind, self);
+    let rhs = dispatch(&rhs.kind, self);
+    lhs + rhs
+  }
+}
+
+#[test]
+fn yolo_swagg() {
+  use super::*;
+
+  let mut t = NumberSummer;
+
+  let x = ExpressionKind::NatLiteral(4);
+
+  let result = dispatch(&x, &mut t);
+  assert_eq!(result, 4);
+}