Add built-in functions.

lib/src/ast/sass/callable_declaration.dart

@@ -0,0 +1,22 @@
+// 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 'package:source_span/source_span.dart';
+
+import 'argument_declaration.dart';
+import 'statement.dart';
+
+abstract class CallableDeclaration implements Statement {
+  final String name;
+
+  final ArgumentDeclaration arguments;
+
+  final List<Statement> children;
+
+  final FileSpan span;
+
+  CallableDeclaration(this.name, this.arguments, Iterable<Statement> children,
+      {this.span})
+      : children = new List.unmodifiable(children);
+}

lib/src/ast/sass/function_declaration.dart

@@ -8,18 +8,10 @@ import '../../visitor/interface/statement.dart';
 import 'argument_declaration.dart';
 import 'statement.dart';
 
-class FunctionDeclaration implements Statement {
-  final String name;
-
-  final ArgumentDeclaration arguments;
-
-  final List<Statement> children;
-
-  final FileSpan span;
-
-  FunctionDeclaration(this.name, this.arguments, Iterable<Statement> children,
-      {this.span})
-      : children = new List.unmodifiable(children);
+class FunctionDeclaration extends CallableDeclaration {
+  FunctionDeclaration(String name, ArgumentDeclaration arguments,
+      Iterable<Statement> children, {FileSpan span})
+      : super(name, arguments, children, span: span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitFunctionDeclaration(this);

lib/src/ast/sass/mixin_declaration.dart

@@ -8,18 +8,10 @@ import '../../visitor/interface/statement.dart';
 import 'argument_declaration.dart';
 import 'statement.dart';
 
-class MixinDeclaration implements Statement {
-  final String name;
-
-  final ArgumentDeclaration arguments;
-
-  final List<Statement> children;
-
-  final FileSpan span;
-
-  MixinDeclaration(this.name, this.arguments, Iterable<Statement> children,
-      {this.span})
-      : children = new List.unmodifiable(children);
+class MixinDeclaration extends CallableDeclaration {
+  MixinDeclaration(String name, ArgumentDeclaration arguments,
+      Iterable<Statement> children, {FileSpan span})
+      : super(name, arguments, children, span: span);
 
   /*=T*/ accept/*<T>*/(StatementVisitor/*<T>*/ visitor) =>
       visitor.visitMixinDeclaration(this);

lib/src/ast/sass/statement.dart

@@ -9,6 +9,7 @@ export 'at_rule.dart';
 export 'argument_declaration.dart';
 export 'argument_invocation.dart';
 export 'argument.dart';
+export 'callable_declaration.dart';
 export 'comment.dart';
 export 'declaration.dart';
 export 'extend_rule.dart';

lib/src/callable.dart

@@ -2,23 +2,13 @@
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-import 'package:source_span/source_span.dart';
-
 import 'ast/sass/statement.dart';
-import 'environment.dart';
 
-class Callable {
-  final String name;
+export 'callable/built_in.dart';
+export 'callable/user_defined.dart';
 
-  final ArgumentDeclaration arguments;
+abstract class Callable {
+  String get name;
 
-  final List<Statement> children;
-
-  final Environment environment;
-
-  final FileSpan span;
-
-  Callable(this.name, this.arguments, Iterable<Statement> children,
-      this.environment, {this.span})
-      : children = new List.unmodifiable(children);
+  ArgumentDeclaration get arguments;
 }

lib/src/callable/built_in.dart

@@ -0,0 +1,20 @@
+// 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/statement.dart';
+import '../callable.dart';
+import '../value.dart';
+
+typedef Value _Callback(List<Value> arguments);
+
+class BuiltInCallable implements Callable {
+  final _Callback callback;
+
+  final String name;
+  final ArgumentDeclaration arguments;
+
+  BuiltInCallable(this.name, this.arguments,
+      Value callback(List<Value> arguments))
+      : callback = callback;
+}

lib/src/callable/user_defined.dart

@@ -0,0 +1,18 @@
+// 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/statement.dart';
+import '../callable.dart';
+import '../environment.dart';
+
+class UserDefinedCallable implements Callable {
+  final CallableDeclaration declaration;
+
+  final Environment environment;
+
+  String get name => declaration.name;
+  ArgumentDeclaration get arguments => declaration.arguments;
+
+  UserDefinedCallable(this.declaration, this.environment);
+}

lib/src/environment.dart

@@ -3,6 +3,7 @@
 // https://opensource.org/licenses/MIT.
 
 import 'callable.dart';
+import 'functions.dart';
 import 'value.dart';
 import 'utils.dart';
 
@@ -27,7 +28,9 @@ class Environment {
         _functions = [normalizedMap()],
         _functionIndices = normalizedMap(),
         _mixins = [normalizedMap()],
-        _mixinIndices = normalizedMap();
+        _mixinIndices = normalizedMap() {
+    defineCoreFunctions(this);
+  }
 
   Environment._(this._variables, this._variableIndices, this._functions,
       this._functionIndices, this._mixins, this._mixinIndices);

lib/src/functions.dart

@@ -0,0 +1,14 @@
+// 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/statement.dart';
+import 'callable.dart';
+import 'environment.dart';
+import 'value.dart';
+
+void defineCoreFunctions(Environment environment) {
+  environment.setFunction(new BuiltInCallable("inspect",
+      new ArgumentDeclaration([new Argument("value")]),
+      (arguments) => new SassIdentifier(arguments.single.toString())));
+}

lib/src/visitor/perform.dart

@@ -40,9 +40,8 @@ class PerformVisitor extends StatementVisitor
 
   final _extender = new Extender();
 
-  PerformVisitor() : this._(new Environment());
-
-  PerformVisitor._(this._environment);
+  PerformVisitor([Environment environment])
+      : _environment = environment ?? new Environment();
 
   void visit(node) {
     if (node is Statement) {
@@ -126,29 +125,27 @@ class PerformVisitor extends StatementVisitor
   }
 
   void visitFunctionDeclaration(FunctionDeclaration node) {
-    _environment.setFunction(new Callable(
-        node.name, node.arguments, node.children, _environment.closure(),
-        span: node.span));
+    _environment.setFunction(
+        new UserDefinedCallable(node, _environment.closure()));
   }
 
   void visitInclude(Include node) {
-    var mixin = _environment.getMixin(node.name);
+    var mixin = _environment.getMixin(node.name) as UserDefinedCallable;
     if (mixin == null) throw node.span.message("Undefined mixin.");
     if (node.children != null) {
       throw node.span.message("Mixin doesn't accept a content block.");
     }
 
-    _runCallable(node.arguments, mixin, node.span, () {
-      for (var statement in mixin.children) {
+    _runUserDefinedCallable(node.arguments, mixin, node.span, () {
+      for (var statement in mixin.declaration.children) {
         statement.accept(this);
       }
     });
   }
 
   void visitMixinDeclaration(MixinDeclaration node) {
-    _environment.setMixin(new Callable(
-        node.name, node.arguments, node.children, _environment.closure(),
-        span: node.span));
+    _environment.setMixin(
+        new UserDefinedCallable(node, _environment.closure()));
   }
 
   void visitMediaRule(MediaRule node) {
@@ -284,14 +281,22 @@ class PerformVisitor extends StatementVisitor
     if (plainName != null) {
       var function = _environment.getFunction(plainName);
       if (function != null) {
-        return _runCallable(node.arguments, function, node.span, () {
-          for (var statement in function.children) {
-            var returnValue = statement.accept(this);
-            if (returnValue is Value) return returnValue;
-          }
+        if (function is BuiltInCallable) {
+          return _runBuiltInCallable(node.arguments, function, node.span);
+        } else if (function is UserDefinedCallable) {
+          return _runUserDefinedCallable(node.arguments, function, node.span,
+              () {
+            for (var statement in function.declaration.children) {
+              var returnValue = statement.accept(this);
+              if (returnValue is Value) return returnValue;
+            }
 
-          throw function.span.message("Function finished without @return.");
-        });
+            throw function.declaration.span.message(
+                "Function finished without @return.");
+          });
+        } else {
+          return null;
+        }
       }
     }
 
@@ -309,8 +314,8 @@ class PerformVisitor extends StatementVisitor
     return new SassIdentifier("$name(${arguments.join(', ')})");
   }
 
-  /*=T*/ _runCallable/*<T>*/(ArgumentInvocation arguments, Callable callable,
-      FileSpan span, /*=T*/ run()) {
+  /*=T*/ _runUserDefinedCallable/*<T>*/(ArgumentInvocation arguments,
+      UserDefinedCallable callable, FileSpan span, /*=T*/ run()) {
     return _withEnvironment(callable.environment, () => _environment.scope(() {
       var pair = _evaluateArguments(arguments, span);
       var positional = pair.first;
@@ -330,7 +335,8 @@ class PerformVisitor extends StatementVisitor
       for (var i = positional.length; i < declaredArguments.length; i++) {
         var argument = declaredArguments[i];
         _environment.setVariable(argument.name,
-            named.remove(argument.name) ?? argument.defaultValue?.accept(this));
+            named.remove(argument.name) ??
+                argument.defaultValue?.accept(this));
       }
 
       // TODO: use a full ArgList object
@@ -349,6 +355,32 @@ class PerformVisitor extends StatementVisitor
     }));
   }
 
+  Value _runBuiltInCallable(ArgumentInvocation arguments,
+      BuiltInCallable callable, FileSpan span) {
+    var pair = _evaluateArguments(arguments, span);
+    var positional = pair.first;
+    var named = pair.last;
+
+    _verifyArguments(positional, named, callable.arguments, span);
+
+    var declaredArguments = callable.arguments.arguments;
+    for (var i = positional.length; i < declaredArguments.length; i++) {
+      var argument = declaredArguments[i];
+      positional.add(named.remove(argument.name) ??
+          argument.defaultValue?.accept(this));
+    }
+
+    // TODO: use a full ArgList object
+    if (callable.arguments.restArgument != null) {
+      var rest = positional.length > declaredArguments.length
+          ? positional.sublist(declaredArguments.length)
+          : const <Value>[];
+      positional.add(new SassList(rest, ListSeparator.comma));
+    }
+
+    return callable.callback(positional);
+  }
+
   Pair<List<Value>, Map<String, Value>> _evaluateArguments(
       ArgumentInvocation arguments, FileSpan span) {
     var positional = arguments.positional