diff --git a/docs/tutorial/LangImpl4.html b/docs/tutorial/LangImpl4.html
index 1048f73..8661b62 100644
--- a/docs/tutorial/LangImpl4.html
+++ b/docs/tutorial/LangImpl4.html
@@ -252,8 +252,9 @@
 add from the program.</p>
 
 <p>LLVM provides a wide variety of optimizations that can be used in certain
-circumstances.  Unfortunately we don't have a good centralized description of
-what every pass does, but you can check out the ones that <tt>llvm-gcc</tt> or
+circumstances.  Some <a href="../Passes.html">documentation about the various 
+passes</a> is available, but it isn't very complete.  Another good source of
+ideas is to look at the passes that <tt>llvm-gcc</tt> or
 <tt>llvm-ld</tt> run to get started.  The "<tt>opt</tt>" tool allows you to 
 experiment with passes from the command line, so you can see if they do
 anything.</p>
@@ -410,6 +411,7 @@
 
 ready&gt; <b>sin(1.0);</b>
 <em>Evaluated to 0.841471</em>
+
 ready&gt; <b>def foo(x) sin(x)*sin(x) + cos(x)*cos(x);</b>
 Read function definition:
 define double @foo(double %x) {
@@ -444,6 +446,27 @@
 function name, and even allows you to have the JIT abort itself if any lazy
 compilation is attempted.</p>
 
+<p>One interesting application of this is that we can now extend the language
+by writing arbitrary C++ code to implement operations.  For example, if we add:
+</p>
+
+<div class="doc_code">
+<pre>
+/// putchard - putchar that takes a double and returns 0.
+extern "C" 
+double putchard(double X) {
+  putchar((char)X);
+  return 0;
+}
+</pre>
+</div>
+
+<p>Now we can produce simple output to the console by using things like:
+"<tt>extern putchard(x); putchard(120);</tt>", which prints a lowercase 'x' on
+the console (120 is the ascii code for 'x').  Similar code could be used to 
+implement file I/O, console input, and many other capabilities in
+Kaleidoscope.</p>
+
 <p>This completes the JIT and optimizer chapter of the Kaleidoscope tutorial. At
 this point, we can compile a non-Turing-complete programming language, optimize
 and JIT compile it in a user-driven way.  Next up we'll look into <a