Merge both perform visitors together.

bin/sass.dart

@@ -6,7 +6,7 @@ import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:sass/src/parser.dart';
-import 'package:sass/src/visitor/perform_statement.dart';
+import 'package:sass/src/visitor/perform.dart';
 import 'package:sass/src/visitor/serialize.dart';
 
 void main(List<String> args) {

lib/src/visitor/perform.dart

@@ -11,11 +11,11 @@ import '../extend/extender.dart';
 import '../parser.dart';
 import '../value.dart';
 import 'interface/statement.dart';
-import 'perform_expression.dart';
+import 'interface/expression.dart';
 
-class PerformVisitor extends StatementVisitor {
+class PerformVisitor extends StatementVisitor
+    implements ExpressionVisitor<Value> {
   final Environment _environment;
-  final PerformExpressionVisitor _expressionVisitor;
 
   /// The current selector, if any.
   CssValue<SelectorList> _selector;
@@ -36,11 +36,17 @@ class PerformVisitor extends StatementVisitor {
 
   PerformVisitor() : this._(new Environment());
 
-  PerformVisitor._(Environment environment)
-      : _environment = environment,
-        _expressionVisitor = new PerformExpressionVisitor(environment);
+  PerformVisitor._(this._environment);
 
-  void visit(Statement node) => node.accept(this);
+  void visit(node) {
+    if (node is Statement) {
+      node.accept(this);
+    } else {
+      (node as Expression).accept(this);
+    }
+  }
+
+  // ## Statements
 
   CssStylesheet visitStylesheet(Stylesheet node) {
     _root = new CssStylesheet(span: node.span);
@@ -183,21 +189,81 @@ class PerformVisitor extends StatementVisitor {
 
   void visitVariableDeclaration(VariableDeclaration node) {
     _environment.setVariable(
-        node.name, node.expression.accept(_expressionVisitor),
+        node.name, node.expression.accept(this),
         global: node.isGlobal);
   }
 
+  // ## Expressions
+
+  Value visitVariableExpression(VariableExpression node) {
+    var result = _environment.getVariable(node.name);
+    if (result != null) return result;
+
+    // TODO: real exception
+    throw node.span.message("undefined variable");
+  }
+
+  Value visitUnaryOperatorExpression(UnaryOperatorExpression node) {
+    var operand = node.operand.accept(this);
+    switch (node.operator) {
+      case UnaryOperator.plus: return operand.unaryPlus();
+      case UnaryOperator.minus: return operand.unaryMinus();
+      case UnaryOperator.divide: return operand.unaryDivide();
+      case UnaryOperator.not: return operand.unaryNot();
+      default: throw new StateError("Unknown unary operator ${node.operator}.");
+    }
+  }
+
+  SassIdentifier visitIdentifierExpression(IdentifierExpression node) =>
+      new SassIdentifier(visitInterpolationExpression(node.text).text);
+
+  SassBoolean visitBooleanExpression(BooleanExpression node) =>
+      new SassBoolean(node.value);
+
+  SassNumber visitNumberExpression(NumberExpression node) =>
+      new SassNumber(node.value);
+
+  SassColor visitColorExpression(ColorExpression node) => node.value;
+
+  SassString visitInterpolationExpression(InterpolationExpression node) {
+    return new SassString(node.contents.map((value) {
+      if (value is String) return value;
+      return (value as Expression).accept(this);
+    }).join());
+  }
+
+  SassList visitListExpression(ListExpression node) => new SassList(
+      node.contents.map((expression) => expression.accept(this)),
+      node.separator,
+      bracketed: node.isBracketed);
+
+  SassMap visitMapExpression(MapExpression node) {
+    var map = <Value, Value>{};
+    for (var pair in node.pairs) {
+      var keyValue = pair.first.accept(this);
+      var valueValue = pair.last.accept(this);
+      if (map.containsKey(keyValue)) {
+        throw pair.first.span.message('Duplicate key.');
+      }
+      map[keyValue] = valueValue;
+    }
+    return new SassMap(map);
+  }
+
+  SassString visitStringExpression(StringExpression node) =>
+      visitInterpolationExpression(node.text);
+
+  // ## Utilities
+
   CssValue<String> _performInterpolation(
       InterpolationExpression interpolation, {bool trim: false}) {
-    var result = _expressionVisitor.visitInterpolationExpression(interpolation)
-        .text;
+    var result = visitInterpolationExpression(interpolation).text;
     return new CssValue(trim ? result.trim() : result,
         span: interpolation.span);
   }
 
   CssValue<Value> _performExpression(Expression expression) =>
-      new CssValue(expression.accept(_expressionVisitor),
-          span: expression.span);
+      new CssValue(expression.accept(this), span: expression.span);
 
   /*=T*/ _withParent/*<S extends CssParentNode, T>*/(
       /*=S*/ node, /*=T*/ callback(),

lib/src/visitor/perform_expression.dart

@@ -1,74 +0,0 @@
-// Copyright 2016 Google Inc. Use of this source code is governed by an
-// MIT-style license that can be found in the LICENSE file or at
-// https://opensource.org/licenses/MIT.
-
-import '../ast/sass/expression.dart';
-import '../environment.dart';
-import '../value.dart';
-import 'interface/expression.dart';
-
-class PerformExpressionVisitor extends ExpressionVisitor<Value> {
-  final Environment _environment;
-
-  PerformExpressionVisitor(this._environment);
-
-  Value visit(Expression expression) => expression.accept(this);
-
-  Value visitVariableExpression(VariableExpression node) {
-    var result = _environment.getVariable(node.name);
-    if (result != null) return result;
-
-    // TODO: real exception
-    throw node.span.message("undefined variable");
-  }
-
-  Value visitUnaryOperatorExpression(UnaryOperatorExpression node) {
-    var operand = node.operand.accept(this);
-    switch (node.operator) {
-      case UnaryOperator.plus: return operand.unaryPlus();
-      case UnaryOperator.minus: return operand.unaryMinus();
-      case UnaryOperator.divide: return operand.unaryDivide();
-      case UnaryOperator.not: return operand.unaryNot();
-      default: throw new StateError("Unknown unary operator ${node.operator}.");
-    }
-  }
-
-  SassIdentifier visitIdentifierExpression(IdentifierExpression node) =>
-      new SassIdentifier(visitInterpolationExpression(node.text).text);
-
-  SassBoolean visitBooleanExpression(BooleanExpression node) =>
-      new SassBoolean(node.value);
-
-  SassNumber visitNumberExpression(NumberExpression node) =>
-      new SassNumber(node.value);
-
-  SassColor visitColorExpression(ColorExpression node) => node.value;
-
-  SassString visitInterpolationExpression(InterpolationExpression node) {
-    return new SassString(node.contents.map((value) {
-      if (value is String) return value;
-      return (value as Expression).accept(this);
-    }).join());
-  }
-
-  SassList visitListExpression(ListExpression node) => new SassList(
-      node.contents.map((expression) => expression.accept(this)),
-      node.separator,
-      bracketed: node.isBracketed);
-
-  SassMap visitMapExpression(MapExpression node) {
-    var map = <Value, Value>{};
-    for (var pair in node.pairs) {
-      var keyValue = pair.first.accept(this);
-      var valueValue = pair.last.accept(this);
-      if (map.containsKey(keyValue)) {
-        throw pair.first.span.message('Duplicate key.');
-      }
-      map[keyValue] = valueValue;
-    }
-    return new SassMap(map);
-  }
-
-  SassString visitStringExpression(StringExpression node) =>
-      visitInterpolationExpression(node.text);
-}