Starting to implement a pretty-printer to test visitor

schala-lang/language/src/ast_visitor.rs

@@ -95,6 +95,43 @@ impl DeclarationVisitor<()> for NullVisitor {
   }
 }
 
+
+#[derive(Default, Clone)]
+struct SchalaPrinter { 
+  s: String
+}
+
+impl ASTVisitor<String> for SchalaPrinter {
+  type EV = SchalaPrinter;
+  type DV = SchalaPrinter;
+  fn ast(&mut self, _: &AST) {
+    self.s.push_str("Pretty-printed AST");
+  }
+
+  fn expression(&mut self) -> Self::EV {
+    SchalaPrinter::default()
+  }
+  fn declaration(&mut self) -> Self::DV {
+    SchalaPrinter::default()
+  }
+
+  fn done(&mut self) -> String {
+    self.s.clone()
+  }
+}
+
+impl ExpressionVisitor<String> for SchalaPrinter {
+  fn done(&mut self) -> String {
+    format!("some_expr")
+  }
+}
+
+impl DeclarationVisitor<String> for SchalaPrinter {
+  fn done(&mut self) -> String {
+    format!("some_decl")
+  }
+}
+
 #[cfg(test)]
 mod visitor_tests {
   use ::tokenizing::{Token, tokenize};