3 files changed, 29 insertions, 4 deletions
diff --git a/demo/demo.js b/demo/demo.js
index 16bd66a6..40e937d0 100644
--- a/demo/demo.js
+++ b/demo/demo.js
@@ -97,7 +97,8 @@ function onError(loc, error, sourceLine, sourceLineColumnOffset) {
   ];
   if (sourceLine.length > 0) {
     var numSpaces = loc.firstColumn - 1 - sourceLineColumnOffset;
-    var numCarets = loc.lastColumn - loc.firstColumn;
+    var numCarets =
+        Math.min(loc.lastColumn - loc.firstColumn, sourceLine.length);
     lines.push(sourceLine);
     lines.push(' '.repeat(numSpaces) + '^'.repeat(numCarets));
   }
@@ -118,6 +119,7 @@ function compile(text) {
       var jsWriter = new wasm.JSStringWriter();
       var logStream = new wasm.Stream(jsWriter.writer);
       var options = new wasm.WriteBinaryOptions({logStream: logStream});
+      wasm.markUsedBlocks(allocator, script);
       wasm.writeBinaryScript(allocator, memoryWriter.base, script, options);
       output.textContent = jsWriter.string;
     } catch (e) {
@@ -181,6 +183,20 @@ var examples = [
       '              (get_local 0)\n' +
       '              (i64.const 1)))))))\n' +
       '  (export "fac" $fac))\n'
+  },
+
+  {
+    name: 'stuff',
+    contents:
+      '(module\n' +
+      '  (memory 1 (segment 0 "hi"))\n' +
+      '  (type (func (param i32) (result i32)))\n' +
+      '  (import "foo" "bar" (param f32))\n' +
+      '  (start 0)\n' +
+      '  (table 0 1)\n' +
+      '  (func)\n' +
+      '  (func (type 0) (i32.const 42))\n' +
+      '  (export "e" 1))\n'
   }
 ];
 
diff --git a/demo/index.html b/demo/index.html
index 6a08d6fd..fecc95b5 100644
--- a/demo/index.html
+++ b/demo/index.html
@@ -27,9 +27,11 @@
     <h1>sexpr-wasm demo</h1>
     <hr>
     <p>
-      Type a .wast file into the textarea on the left. The right side will
+      Type a <a href="https://github.com/WebAssembly/spec/tree/master/ml-proto#s-expression-syntax">.wast</a>
+      file into the textarea on the left. The right side will
       either show an error, or will show a log with a description of the
-      generated .wasm file.
+      generated <a href="https://github.com/WebAssembly/design/blob/master/BinaryEncoding.md">.wasm</a>
+      file.
     </p>
     <div class="columns">
       <div class="two-fifths column">
@@ -45,7 +47,7 @@
       </div>
     </div>
   </div>
-  <script src="libwasm.js"></script>
+  <script src="libwasm-debug.js"></script>
   <script src="demo.js"></script>
 </body>
 </html>
diff --git a/src/wasm.js b/src/wasm.js
index 25175686..5a2b4a08 100644
--- a/src/wasm.js
+++ b/src/wasm.js
@@ -485,6 +485,12 @@ var checkAst = function(lexer, script, errorHandler) {
     throw "checkAst failed";
 };
 
+var markUsedBlocks = function(allocator, script) {
+  var result = Module._wasm_mark_used_blocks(allocator.$addr, script.$addr);
+  if (result != OK)
+    throw "markUsedBlocks failed";
+};
+
 var writeBinaryScript = function(allocator, writer, script, options) {
   var result = Module._wasm_write_binary_script(allocator.$addr, writer.$addr,
                                                 script.$addr, options.$addr);
@@ -517,6 +523,7 @@ wasm = {
   Writer: Writer,
 
   checkAst: checkAst,
+  markUsedBlocks: markUsedBlocks,
   parse: parse,
   writeBinaryScript: writeBinaryScript,
 };