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diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Argument.java b/src/main/java/com/google/devtools/build/lib/syntax/Argument.java
new file mode 100644
index 0000000000..0706dee8bc
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+++ b/src/main/java/com/google/devtools/build/lib/syntax/Argument.java
@@ -0,0 +1,122 @@
+// Copyright 2014 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.syntax;
+
+/**
+ * Syntax node for a function argument. This can be a key/value pair such as
+ * appears as a keyword argument to a function call or just an expression that
+ * is used as a positional argument. It also can be used for function definitions
+ * to identify the name (and optionally the default value) of the argument.
+ */
+public final class Argument extends ASTNode {
+
+  private final Ident name;
+
+  private final Expression value;
+
+  private final boolean kwargs;
+
+  /**
+   * Create a new argument.
+   * At call site: name is optional, value is mandatory. kwargs is true for ** arguments.
+   * At definition site: name is mandatory, (default) value is optional.
+   */
+  public Argument(Ident name, Expression value, boolean kwargs) {
+    this.name = name;
+    this.value = value;
+    this.kwargs = kwargs;
+  }
+
+  public Argument(Ident name, Expression value) {
+    this.name = name;
+    this.value = value;
+    this.kwargs = false;
+  }
+
+  /**
+   * Creates an Argument with null as name. It can be used as positional arguments
+   * of function calls.
+   */
+  public Argument(Expression value) {
+    this(null, value);
+  }
+
+  /**
+   * Creates an Argument with null as value. It can be used as a mandatory keyword argument
+   * of a function definition.
+   */
+  public Argument(Ident name) {
+    this(name, null);
+  }
+
+  /**
+   * Returns the name of this keyword argument or null if this argument is
+   * positional.
+   */
+  public Ident getName() {
+    return name;
+  }
+
+  /**
+   * Returns the String value of the Ident of this argument. Shortcut for arg.getName().getName().
+   */
+  public String getArgName() {
+    return name.getName();
+  }
+
+  /**
+   * Returns the syntax of this argument expression.
+   */
+  public Expression getValue() {
+    return value;
+  }
+
+  /**
+   * Returns true if this argument is positional.
+   */
+  public boolean isPositional() {
+    return name == null && !kwargs;
+  }
+
+  /**
+   * Returns true if this argument is a keyword argument.
+   */
+  public boolean isNamed() {
+    return name != null;
+  }
+
+  /**
+   * Returns true if this argument is a **kwargs argument.
+   */
+  public boolean isKwargs() {
+    return kwargs;
+  }
+
+  /**
+   * Returns true if this argument has value.
+   */
+  public boolean hasValue() {
+    return value != null;
+  }
+
+  @Override
+  public String toString() {
+    return isNamed() ? name + "=" + value : String.valueOf(value);
+  }
+
+  @Override
+  public void accept(SyntaxTreeVisitor visitor) {
+    visitor.visit(this);
+  }
+}