--- a/graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/local/SLReadArgumentNode.java	Thu Jan 30 17:52:24 2014 -0800
+++ b/graal/com.oracle.truffle.sl/src/com/oracle/truffle/sl/nodes/local/SLReadArgumentNode.java	Thu Jan 30 17:53:27 2014 -0800
@@ -22,15 +22,31 @@
  */
 package com.oracle.truffle.sl.nodes.local;
 
+import com.oracle.truffle.api.*;
 import com.oracle.truffle.api.frame.*;
 import com.oracle.truffle.api.utilities.*;
 import com.oracle.truffle.sl.nodes.*;
+import com.oracle.truffle.sl.parser.*;
 import com.oracle.truffle.sl.runtime.*;
 
+/**
+ * Reads a function argument. Arguments are passed in as a {@link SLArguments} object, which
+ * encapsulates an {@link SLArguments#getFromFrame Object[] array}. Language-defined subclasses of
+ * {@link Arguments} are the standard Truffle way to pass values between function.
+ * <p>
+ * Arguments are not type-specialized. To ensure that repeated accesses within a method are
+ * specialized and can, e.g., accessed without unboxing, all arguments are loaded into local
+ * variables {@link SLNodeFactory#addFormalParameter in the method prologue}.
+ */
 public class SLReadArgumentNode extends SLExpressionNode {
 
+    /** The argument number, i.e., the index into the array of arguments. */
     private final int index;
 
+    /**
+     * Profiling information, collected by the interpreter, capturing whether the function was
+     * called with fewer actual arguments than formal arguments.
+     */
     private final BranchProfile outOfBoundsTaken = new BranchProfile();
 
     public SLReadArgumentNode(int index) {
@@ -43,7 +59,9 @@
         if (index < args.length) {
             return args[index];
         } else {
+            /* In the interpreter, record profiling information that the branch was used. */
             outOfBoundsTaken.enter();
+            /* Use the default null value. */
             return SLNull.SINGLETON;
         }
     }