Infrastructure for separate-object block handler

Requires one unstable feature

schala-lang/language/src/ast/visitor.rs

@@ -5,8 +5,10 @@ use crate::ast::*;
 //or a tuple of (T, <that type>)
 
 pub trait ASTVisitor: Sized {
+  type BlockHandler: BlockVisitor = ();
   fn ast(&mut self, _ast: &AST) {}
-  fn block(&mut self, _statements: &Vec<Statement>) {}
+  fn block(&mut self) -> Self::BlockHandler { Self::BlockHandler::new() }
+  fn block_finished(&mut self, handler: Self::BlockHandler) {}
   fn statement(&mut self, _statement: &Statement) {}
   fn declaration(&mut self, _declaration: &Declaration) {}
   fn signature(&mut self, _signature: &Signature) {}
@@ -39,3 +41,15 @@ pub trait ASTVisitor: Sized {
   fn prefix_exp(&mut self, _op: &PrefixOp, _arg: &Expression) {}
   fn pattern(&mut self, _pat: &Pattern) {}
 }
+
+pub trait BlockVisitor {
+  fn new() -> Self;
+  fn pre_block(&mut self) {}
+  fn post_block(&mut self) {}
+}
+
+impl BlockVisitor for () {
+  fn new() -> () { () }
+}
+
+

schala-lang/language/src/ast/walker.rs

@@ -1,7 +1,7 @@
 #![allow(dead_code)]
 use std::rc::Rc;
 use crate::ast::*;
-use crate::ast::visitor::ASTVisitor;
+use crate::ast::visitor::{ASTVisitor, BlockVisitor};
 use crate::util::deref_optional_box;
 
 pub fn walk_ast<V: ASTVisitor>(v: &mut V, ast: &AST) {
@@ -10,10 +10,14 @@ pub fn walk_ast<V: ASTVisitor>(v: &mut V, ast: &AST) {
 }
 
 fn walk_block<V: ASTVisitor>(v: &mut V, block: &Vec<Statement>) {
+  let mut block_handler = v.block();
+  block_handler.pre_block();
   for s in block {
     v.statement(s);
     statement(v, s);
   }
+  block_handler.post_block();
+  v.block_finished(block_handler);
 }
 
 fn statement<V: ASTVisitor>(v: &mut V, statement: &Statement) {
@@ -44,7 +48,6 @@ fn declaration<V: ASTVisitor>(v: &mut V, decl: &Declaration) {
     },
     FuncDecl(sig, block) => {
       v.signature(&sig);
-      v.block(&block);
       walk_block(v, block);
     },
     TypeDecl { name, body, mutable  } => v.type_declaration(name, body, *mutable),
@@ -123,7 +126,6 @@ fn lambda<V: ASTVisitor>(v: &mut V, params: &Vec<FormalParam>, type_anno: Option
     formal_param(v, param);
   }
   v.type_annotation(type_anno);
-  v.block(body);
   walk_block(v, body);
 }
 
@@ -234,7 +236,6 @@ fn condition_arm<V: ASTVisitor>(v: &mut V, arm: &ConditionArm) {
     v.expression(guard);
     expression(v, guard);
   });
-  v.block(&arm.body);
   walk_block(v, &arm.body);
 }
 

schala-lang/language/src/lib.rs

@@ -1,6 +1,5 @@
+#![feature(associated_type_defaults)] //needed for Visitor trait
 #![feature(trace_macros)]
-#![feature(custom_attribute)]
-//#![feature(unrestricted_attribute_tokens)]
 #![feature(slice_patterns, box_patterns, box_syntax)]
 
 //! `schala-lang` is where the Schala programming language is actually implemented.