Starting to add some more structure

schala-lang/language/src/ast_visitor.rs

@@ -5,17 +5,23 @@ pub fn dispatch<T, V: ASTVisitor<T>>(visitor: &mut V, ast: &AST) -> T {
   for statement in ast.0.iter() {
     visitor.statement(statement);
     match statement {
-      Statement::ExpressionStatement(expr) => visitor.expression(expr),
+      Statement::ExpressionStatement(expr) => {
+        let ref mut expression_visitor = visitor.expression();
+        dispatch_expression(expression_visitor, expr);
+      },
       Statement::Declaration(decl) => {
         visitor.declaration(decl);
         match decl {
           Declaration::FuncSig(sig) => visitor.func_signature(sig),
           Declaration::FuncDecl(sig, block) => visitor.func_declaration(sig, block),
+          _ => unimplemented!(),
+          /*
           Declaration::TypeDecl { .. } => unimplemented!(),
           Declaration::TypeAlias(..) => unimplemented!(), 
           Declaration::Binding { .. } => unimplemented!(),
           Declaration::Impl { .. } => unimplemented!(),
           Declaration::Interface { .. } => unimplemented!(),
+          */
         };
         visitor.decl_done();
       }
@@ -25,6 +31,8 @@ pub fn dispatch<T, V: ASTVisitor<T>>(visitor: &mut V, ast: &AST) -> T {
 }
 
 pub trait ASTVisitor<T> {
+  type EV : ExpressionVisitor<T>;
+
   fn ast(&mut self, ast: &AST) {
   }
   fn done(&mut self) -> T;
@@ -43,9 +51,18 @@ pub trait ASTVisitor<T> {
   fn func_declaration(&mut self, sig: &Signature, block: &Vec<Statement>) {
   }
 
-  fn expression(&mut self, statement: &Expression) {
+  fn expression(&mut self) -> Self::EV;
-  }
+}
 
+pub fn dispatch_expression<T, V: ExpressionVisitor<T>>(visitor: &mut V, expr: &Expression) -> T {
+  visitor.expression(expr);
+  visitor.done()
+}
+
+pub trait ExpressionVisitor<T> {
+  fn expression(&mut self, expression: &Expression) {
+  }
+  fn done(&mut self) -> T;
 }
 
 /*----*/
@@ -53,6 +70,7 @@ pub trait ASTVisitor<T> {
 
 struct NullVisitor { }
 impl ASTVisitor<()> for NullVisitor {
+  type EV = NullVisitor;
   fn done(&mut self) -> () {
     ()
   }
@@ -60,5 +78,15 @@ impl ASTVisitor<()> for NullVisitor {
   fn decl_done(&mut self) -> () {
     ()
   }
+
+  fn expression(&mut self) -> Self::EV {
+    NullVisitor { }
+  }
+}
+
+impl ExpressionVisitor<()> for NullVisitor {
+  fn done(&mut self) -> () {
+    ()
+  }
 }