MIR: lexical scoping + builder vars modules

src/mir/builder/exprs.rs

@@ -21,6 +21,7 @@ impl super::MirBuilder {
                 // Sequentially lower statements and return last value (or Void)
                 self.cf_block(statements)
             }
+            ASTNode::ScopeBox { body, .. } => self.cf_block(body),
             ASTNode::Print { expression, .. } => self.build_print_statement(*expression),
             ASTNode::If {
                 condition,